/*
** This file is part of the Brandy Basic V Interpreter.
** Copyright (C) 2000, 2001, 2002, 2003, 2004 David Daniels
**
** Brandy is free software; you can redistribute it and/or modify
** it under the terms of the GNU General Public License as published by
** the Free Software Foundation; either version 2, or (at your option)
** any later version.
**
** Brandy is distributed in the hope that it will be useful,
** but WITHOUT ANY WARRANTY; without even the implied warranty of
** MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
** GNU General Public License for more details.
**
** You should have received a copy of the GNU General Public License
** along with Brandy; see the file COPYING.  If not, write to
** the Free Software Foundation, 59 Temple Place - Suite 330,
** Boston, MA 02111-1307, USA.
**
**
**	This file contains the bulk of the Basic interpreter itself
*/

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
#include <errno.h>
#include "common.h"
#include "target.h"
#include "basicdefs.h"
#include "tokens.h"
#include "variables.h"
#include "stack.h"
#include "heap.h"
#include "strings.h"
#include "errors.h"
#include "statement.h"
#include "evaluate.h"
#include "convert.h"
#include "miscprocs.h"
#include "editor.h"
#include "emulate.h"
#include "screen.h"
#include "lvalue.h"
#include "fileio.h"
#include "mainstate.h"

#define MAXWHENS 500		/* maximum number of WHENs allowed per CASE statement */
#define MAXSYSPARMS 10		/* Maximum number of parameters allowed in a 'SYS' statement */

/*
** 'exec_assembler' is invoked when a '[' is found. This version of
** the interpreter does not include an assembler
*/
void exec_assembler(void) {
  error(ERR_UNSUPPORTED);
}

/*
** 'exec_asmend' is called with a ']' is found. This version of
** the interpreter does not include an assembler
*/
void exec_asmend(void) {
  error(ERR_UNSUPPORTED);
}

/*
** 'exec_oscmd' deals with '*' commands. The text of the '*' is
** retrieved from the source part of the line and passed to the
** operating system as a command. The effect of a command that
** overwrites the Basic program or the interpreter is undefined.
*/
void exec_oscmd(void) {
  char *p;
  p = CAST(get_srcaddr(basicvars.current), char *);	/* Get the address of the command text */
  emulate_oscli(p, FALSE);		/* Run command but do not capture output */
  basicvars.current+=1+SIZESIZE;	/* Skip the '*' and the offset after it */
}

/*
** 'exec_call' deals with the Basic 'CALL' statement. This is not
** supported at the moment
*/
void exec_call(void) {
  int32 address, parmcount, parameters[1];
  basicvars.current++;
  parmcount = 0;
  address = eval_integer();
  check_ateol();
  emulate_call(address, parmcount, parameters);
}

/*
** 'exec_case' deals with a 'CASE' statement.
** The way 'CASE' statements are handled is to build a table of pointers to
** expressions and statement sequences the first time the statement is seen.
** This eliminates the need to search for the 'WHEN' clauses each time the
** statement is executed (at the expense of some extra memory).
*/
void exec_case(void) {
  stackitem casetype, whentype;
  int32 n, intcase = 0;
  static float64 floatcase;
  basicstring casestring = {0, NULL}, whenstring;
  casetable *cp;
  boolean found;
  byte *here;
  here = basicvars.current;
  cp = GET_ADDRESS(basicvars.current, casetable *);	/* Fetch address of 'CASE' table */
  basicvars.current+=1+LOFFSIZE;		/* Skip 'CASE' token and pointer */
  expression();
  casetype = GET_TOPITEM;
  switch (casetype) {	/* Check the type of the 'CASE' expression */
  case STACK_INT:
    intcase = pop_int();
    break;
  case STACK_FLOAT:
    floatcase = pop_float();
    break;
  case STACK_STRING: case STACK_STRTEMP:
    casestring = pop_string();
    break;
  default:
    error(ERR_VARNUMSTR);
  }
/*
** Now go through the case table and try to find a 'WHEN' case that
** matches
*/
  found = FALSE;
  for (n=0; n<cp->whencount; n++) {
    basicvars.current = cp->whentable[n].whenexpr;	/* Point at the WHEN expression */
    if (basicvars.traces.lines) trace_line(get_lineno(find_linestart(basicvars.current)));
    while (TRUE) {
      expression();
      whentype = GET_TOPITEM;
      if (casetype == STACK_INT) {	/* Go by type of 'case' expression */
        if (whentype == STACK_INT)	/* Then by type of 'WHEN' expression */
          found = pop_int() == intcase;
        else if (whentype == STACK_FLOAT)
          found = pop_float() == TOFLOAT(intcase);
        else {
          error(ERR_TYPENUM);
        }
      }
      else if (casetype == STACK_FLOAT) {		/* 'case' expression is a floating point value */
        if (whentype == STACK_INT)
          found = TOFLOAT(pop_int()) == floatcase;
        else if (whentype == STACK_FLOAT)
          found = pop_float() == floatcase;
        else {
          error(ERR_TYPENUM);
        }
      }
      else {	/* This leaves just strings */
        if (whentype != STACK_STRING && whentype != STACK_STRTEMP) error(ERR_TYPESTR);
        whenstring = pop_string();
        if (whenstring.stringlen != casestring.stringlen)
          found = FALSE;
        else if (whenstring.stringlen == 0)
          found = TRUE;
        else {
          found = memcmp(whenstring.stringaddr, casestring.stringaddr, whenstring.stringlen) == 0;
        }
        if (whentype == STACK_STRTEMP) free_string(whenstring);
      }
      if (found || *basicvars.current == ':' || *basicvars.current == NUL) break;	/* Found a match or end of WHEN expression list so escape from loop */
      if (*basicvars.current == ',')	/* No match - Another value follows for this CASE */
        basicvars.current++;
      else {
        error(ERR_SYNTAX);
      }
    }
    if (found) break;	/* Match found - Escape from outer loop */
  }
  if (casetype == STACK_STRTEMP) free_string(casestring);
  if (found) {	/* Case value matched */
    if (basicvars.traces.branches) trace_branch(here, cp->whentable[n].whenaddr);
    basicvars.current = cp->whentable[n].whenaddr;
  }
  else {	/* Case value not matched - Use 'OTHERWISE' entry */
    if (basicvars.traces.branches) trace_branch(here, cp->defaultaddr);
    basicvars.current = cp->defaultaddr;
  }
}

/*
** 'exec_xcase' is called the first time a case statement is seen to go
** through the statement and build a case table for it. Each entry of
** this consists of pair of addresses, one for an expression and one for
** the code after the 'WHEN'. On entry, 'current' points at the address
** of the 'XCASE' token
*/
void exec_xcase(void) {
  byte *tp, *lp, *defaultaddr;
  int32 whencount, depth, n;
  casetable *cp;
  whenvalue whentable[MAXWHENS];
  lp = basicvars.current;
  do {	/* Find the end of the current line */
    tp = lp;
    lp = skip_token(lp);
  } while (*lp != NUL);
  if (*tp != TOKEN_OF) error(ERR_OFMISS);		/* Last item on line must be 'OF' */
  lp++;		/* Point at the start of the line after the 'CASE' */
  whencount = 0;
  defaultaddr = NIL;
  depth = 1;
  while (depth>0) {
    if (AT_PROGEND(lp)) error(ERR_ENDCASE);	/* No ENDCASE found for this CASE */
    tp = FIND_EXEC(lp);		/* Find the first executable token */
    switch (*tp) {
    case TOKEN_XWHEN: case TOKEN_WHEN:	/* Have found a 'WHEN' */
      tp+=(1+OFFSIZE);	/* Skip token and the offset after it */
      if (depth == 1) {	/* Only want WHENs from CASE at this level */
        if (whencount == MAXWHENS) error(ERR_WHENCOUNT);
        whentable[whencount].whenexpr = tp;
        while (*tp != NUL && *tp != ':') tp = skip_token(tp);	/* Find code after ':' */
        if (*tp == ':') tp++;
        if (*tp == NUL) {	/* At end of line - Skip to next line */
          tp++;
          tp = FIND_EXEC(tp);
        }
        whentable[whencount].whenaddr = tp;
        whencount++;
      }
      break;
    case TOKEN_XOTHERWISE: case TOKEN_OTHERWISE:	/* Have found an 'OTHERWISE' */
      if (depth == 1) {
        tp+=(1+OFFSIZE);	/* Skip token and the offset after it */
        if (*tp == ':') tp++;
        if (*tp == NUL) {	/* 'OTHERWISE' is at end of line */
          tp++;	/* Move to start of next line */
          if (AT_PROGEND(tp)) error(ERR_ENDCASE);
          tp = FIND_EXEC(tp);
        }
        defaultaddr = tp;
      }
      break;
    case TOKEN_ENDCASE:	/* Have reached the end of the statement */
      depth--;
      if (depth == 0 && defaultaddr == NIL) defaultaddr = tp+1;
      break;
    }
/* See if a nested CASE statement starts on this line */
    if (depth>0) {
      tp = FIND_EXEC(lp);
      while (*tp != NUL && *tp != TOKEN_XCASE) tp = skip_token(tp);
      if (*tp == TOKEN_XCASE) depth++;
      lp+=GET_LINELEN(lp);
    }
  }
/* Create 'CASE' table */
  cp = allocmem(sizeof(casetable)+whencount*sizeof(whenvalue));	/* Hacksville, Tennessee */
  cp->whencount = whencount;
  cp->defaultaddr = defaultaddr;
  for (n=0; n<whencount; n++) cp->whentable[n] = whentable[n];
  *basicvars.current = TOKEN_CASE;
  set_address(basicvars.current, cp);
  exec_case();	/* Now go and process the CASE statement */
}

/*
** 'exec_chain' deals with the Basic 'CHAIN' statement. It is a bit
** nasty in that the way it works is by loading the new program and
** then resetting the current pointer to the start of the program
** without letting anyone know what it has done
*/
void exec_chain(void) {
  basicstring namedesc;
  stackitem stringtype;
  char *filename;
  basicvars.current++;
  expression();
  stringtype = GET_TOPITEM;
  if (stringtype != STACK_STRING && stringtype != STACK_STRTEMP) error(ERR_TYPESTR);
  namedesc = pop_string();
  filename = tocstring(namedesc.stringaddr, namedesc.stringlen);
  if (stringtype == STACK_STRTEMP) free_string(namedesc);
  check_ateol();
  clear_error();	/* Clear the decks and read the new program */
  read_basic(filename);
  init_expressions();	/* Initialise the expression evaluation code */
  basicvars.datacur = NIL;
  basicvars.curcount = 0;
  basicvars.runflags.outofdata = FALSE;
  basicvars.current = FIND_EXEC(basicvars.start);	/* Find place at which to start new program */
}

/*
** 'exec_clear' is called to clear all the variables defined in the
** program and remove all references to them from the tokenised program.
** It also clears the Basic stack so it is not a good idea to use it
** in a procedure or function. It probably will not crash the interpreter
** but there is no guarantee of this.
*/
void exec_clear(void) {
  basicvars.current++;	/* Move past token */
  check_ateol();
  clear_varptrs();
  clear_varlists();
  clear_strings();
  clear_heap();
  clear_stack();
  init_expressions();
}

/*
** 'exec_data' hendles the 'DATA' statement when one of these is
** encountered in normal program execution. The DATA token will
** always be the last thing on the line. It moves the current
** pointer to the NUL at the end of the line
*/
void exec_data(void) {
  basicvars.current = skip_token(basicvars.current);
}

/*
** 'exec_def' processes 'DEF'-type statements. It is an error in
** this interpreter to run into a procedure or multi-line function
*/
void exec_def(void) {
  byte *tp, *base;
  basicvars.current++;		/* Skip the DEF token */
  if (*basicvars.current != TOKEN_XFNPROCALL) {		/* Not followed by PROC or FN so ignore rest of line */
    while (!ateol[*basicvars.current]) basicvars.current = skip_token(basicvars.current);
    return;
  }
  tp = get_srcaddr(basicvars.current);		/* Find name of PROC or FN */
  if (*tp == TOKEN_PROC) error(ERR_CRASH);	/* Have run into a procedure */
/* This leaves just functions. Check for single line function */
  tp = basicvars.current+1+LOFFSIZE;
  if (*tp == '(') {	/* Function name is followed by a parameter list */
    tp++;
    while (!ateol[*tp]) {	/* Find end of parameter list */
      if (*tp == TOKEN_RETURN) tp++;	/* Return parameter */
      if (*tp == TOKEN_XVAR) {		/* Found a parameter */
        base = tp;
        tp+=1+LOFFSIZE;
        if (*tp == ')') {		/* Could mark an array or the end of the parameters */
          base = get_srcaddr(base);
          if (*(skip_name(base)-1) == '(') tp++;	/* Got 'name()' - Found an array */
        }
      }
      else if (*tp == TOKEN_STATICVAR)	/* Found a static variable */
        tp+=2;
      else {
        error(ERR_SYNTAX);
      }
      if (*tp == ')') break;	/* Found end of parameter list */
      if (*tp != ',') error(ERR_SYNTAX);
      tp++;	/* Skip the ',' */
    }
    if (*tp == ')') tp++;	/* Skip the ')' */
/* Check if token after the function name (and optional parameter list) is a '=' */
  }
  if (*tp != '=') error(ERR_CRASH);	/* Not an '=' - Flag error */
  do	/* Single line function - Skip to end of statement */
    tp = skip_token(tp);
  while (!ateol[*tp]);
  basicvars.current = tp;
}

/*
** define_byte_array - Called to handle a DIM of the form:
**   DIM <name> <size>
*/
static void define_byte_array(variable *vp) {
  boolean isindref, islocal;
  int32 offset = 0, highindex;
  byte *ep;
/*
** Allocate a byte *array* (index range 0..highindex) of the requested
** size. The address stored is in fact the byte offset of the array
** from the start of the Basic workspace
*/
  if (vp->varflags  !=  VAR_INTWORD && vp->varflags  !=  VAR_FLOAT) error(ERR_VARNUM);
  isindref = *basicvars.current == '!';
  if (isindref) {
/* Deal with indirection operator in DIM <variable>!<offset> <size> */
    basicvars.current++;
    if (vp->varflags == VAR_INTWORD)
      offset = vp->varentry.varinteger + eval_intfactor();
    else {
      offset = TOINT(vp->varentry.varfloat) + eval_intfactor();
    }
  }
  islocal = *basicvars.current == TOKEN_LOCAL;
  if (islocal) {	/* Allocating block on stack */
    if (basicvars.procstack == NIL) error(ERR_LOCAL);	/* LOCAL found outside a PROC or FN */
    basicvars.current++;
    highindex = eval_integer();
    if (highindex < 0) error(ERR_NEGDIM, vp->varname);	/* Dimension is out of range */
    ep = alloc_stackmem(highindex + 1);			/* Allocate memory on the stack */
    if (ep == NIL) error(ERR_BADBYTEDIM, vp->varname);	/* Not enough memory left */
  }
  else {	/* Allocating block from heap */
    highindex = eval_integer();
    if (highindex < -1) error(ERR_NEGDIM, vp->varname);	/* Dimension is out of range */

    if (highindex == -1)	/* Treat size of -1 as special case, although it does not have to be */
      ep = basicvars.vartop;
    else {
      ep = condalloc(highindex+1);
      if (ep == NIL) error(ERR_BADBYTEDIM, vp->varname);	/* Not enough memory left */
    }
  }
  if (isindref)
    store_integer(offset, ep-basicvars.offbase);
  else if (vp->varflags == VAR_INTWORD)
    vp->varentry.varinteger = ep-basicvars.offbase;
  else {
    vp->varentry.varfloat = TOFLOAT(ep-basicvars.offbase);
  }
}

/*
** 'exec_dim' is called to handle DIM statements
*/
void exec_dim(void) {
  byte *base, *ep;
  variable *vp;
  boolean blockdef;		/* TRUE if we are allocating a block of memory and not creating an array */
  boolean islocal;		/* TRUE if we are defining a local array on the stack */
  do {
    basicvars.current++;	/* Skip 'DIM' token or ',' */
/* Must always have a variable name next */
    if (*basicvars.current != TOKEN_STATICVAR && *basicvars.current != TOKEN_XVAR) error(ERR_NAMEMISS);
    islocal = FALSE;		/* Assume item is not a local array */
    if (*basicvars.current == TOKEN_STATICVAR) {	/* Found a static variable */
      vp = &basicvars.staticvars[*(basicvars.current+1)];
      base = basicvars.current;
      basicvars.current+=2;
      blockdef = TRUE;	/* Can only be defining a block of memory */
    }
    else {	/* Found dynamic variable or array name */
      base = get_srcaddr(basicvars.current);	/* Point 'base' at start of array name */
      ep = skip_name(base);			/* Point ep at byte after name */
      basicvars.current+=1+LOFFSIZE;		/* Skip the pointer to the name */
      blockdef = *(ep-1) != '(' && *(ep-1) != '[';
      vp = find_variable(base, ep-base);
      if (blockdef) {	/* Defining a block of memory (byte array) */
        if (vp == NIL) {		/* Variable does not exist */
          if (*basicvars.current == '!')	/* Variable name followed by indirection operator */
            error(ERR_VARMISS, tocstring(CAST(base, char *), ep-base));
          else {	/* Reference to variable only - Create the variable */
            vp = create_variable(base, ep-base, NIL);
          }
        }
      }
      else if (vp == NIL)	/* Defining an array - Array does not exist yet */
        vp = create_variable(base, ep-base, NIL);
      else {	/* Array name exists */
        if (vp->varentry.vararray != NIL) error(ERR_DUPLDIM, vp->varname);	/* Array aleady defined */
        islocal = TRUE;	/* Name exists but definition does not. Assume a local array */
      }
    }
    if (blockdef)	/* Defining a block of memory */
      define_byte_array(vp);
    else {	/* Defining a normal array */
      define_array(vp, islocal);
    }
  } while (*basicvars.current == ',');
  check_ateol();
}

/*
** 'start_blockif' returns 'TRUE' if the line starting at 'tp' marks the
** start of a block 'IF' statement
*/
static boolean start_blockif(byte *tp) {
  while (*tp != NUL) {
    if (*tp == TOKEN_THEN && *(tp+1) == NUL) return TRUE;
    tp = skip_token(tp);
  }
  return FALSE;
}

/*
** 'exec_elsewhen' deals with an ELSE keyword for both block and single
** line IF statements as well as the 'WHEN' and 'OTHERWISE' keywords in
** a 'CASE' statement. In all cases, the keyword marks the end of one of
** more statements and a branch to another part of the code (the code
** after the ENDIF or ENDCASE) is needed.
** On entry, basicvars.current points at the token for the keyword. The
** offset is in the two bytes that follow. 'GET_DEST' differs from most
** of the other macros used to manipulate offsets and pointers in that
** the argument has to point at the offset and not at the byte before it.
** The reason for this is that there can be more than one offset in
** a row, for example, after an 'IF' token
*/
void exec_elsewhen(void) {
  byte *p;
  p = basicvars.current+1;	/* Point at offset */
  p = GET_DEST(p);
  if (basicvars.traces.enabled) {
    if (basicvars.traces.lines) trace_line(get_lineno(find_linestart(p)));
    if (basicvars.traces.branches) trace_branch(basicvars.current, p);
  }
  basicvars.current = p;
}

/*
** 'exec_xelse' deals with the first reference to an ELSE in a single line
** IF statement. It fills in the offset to reach the next line
*/
void exec_xelse(void) {
  byte *p;
  *basicvars.current = TOKEN_ELSE;
  p = basicvars.current+1+OFFSIZE;	/* Start at the token after the offset */
  do
    p = skip_token(p);
  while (*p != NUL);
  p++;	/* Point at start of next line */
  set_dest(basicvars.current+1, FIND_EXEC(p));
  exec_elsewhen();
}

/*
** 'exec_xlhelse' deals with the first reference to an 'ELSE' that is part
** of a block 'IF' statement. It will be encountered after executing the
** statements following the 'THEN' part of the 'IF'. It locates the 'ENDIF'
** and fills in the offset to the next statement after the 'ENDIF' after
** the 'ELSE' token. Note that it is possible for there to be a statement
** on the same line as the 'ELSE' so the search starts there. The 'ENDIF'
** has to be the first token on a line.
*/
void exec_xlhelse(void) {
  int32 depth;
  byte *lp, *lp2;
  lp = find_linestart(basicvars.current);	/* Find the start of the line with the 'ELSE' */
  lp2 = basicvars.current;	/* Ensure the code won't find an ENDIF first thing */
  depth = 1;
  do {	/* Look for the matching ENDIF */
    if (*lp2 == TOKEN_ENDIF) depth--;
    if (start_blockif(lp2)) depth++;	/* Scan line to see if another block 'IF' starts in it */
    if (depth == 0) break;
    lp+=GET_LINELEN(lp);
    if (AT_PROGEND(lp)) error(ERR_ENDIF);	/* No ENDIF found */
    lp2 = FIND_EXEC(lp);
  } while (TRUE);
  lp2++;	/* Skip the ENDIF token */
  if (*lp2 == NUL) {	/* There is nothing else on the line after the ENDIF */
    lp2++;	/* Move to start of next line */
    if (basicvars.traces.lines) trace_line(get_lineno(lp2));
    lp2 = FIND_EXEC(lp2);	/* Find the first executable token */
  }
  *basicvars.current = TOKEN_LHELSE;
  set_dest(basicvars.current+1, lp2);	/* Set destination of branch */
  exec_elsewhen();
}

/*
** 'exec_end' executes an 'END' statement. The normal use of 'END'
** is to end a program, but under RISC OS the form 'END=<value>' can
** be used to extend the memory available to the program above the
** top of the Basic stack to give a user-controlled heap. In this
** version of the interpreter, this statement form is recognised
** but has no effect
**
** If being used to finish a program, all it does is return to the
** command loop after closing any open files (if that option is
** in effect)
*/
void exec_end(void) {
  int32 newend = 0;
  basicvars.current++;		/* Skip END token */
  if (*basicvars.current == '=') {	/* Have got 'END=' version */
    basicvars.current++;
    expression();
    check_ateol();
    switch(GET_TOPITEM) {
    case STACK_INT:
      newend = pop_int();
      break;
    case STACK_FLOAT:
      newend = TOINT(pop_float());
      break;
    default:
      error(ERR_TYPENUM);
    }
    emulate_endeq(newend);
  }
  else {	/* Normal 'END' statement */
    check_ateol();
    end_run();
  }
}

/*
** 'exec_endifcase' is called when an 'ENDCASE' or an 'ENDIF' statement
** is found. In the normal case of events these are skipped automatically
** by the 'WHEN' and 'ELSE' code but it is not an error if they are
** encountered during normal program execution. They act as 'no op's in
** this case
*/
void exec_endifcase(void) {
  basicvars.current++;		/* Skip token */
  if (!ateol[*basicvars.current]) error(ERR_SYNTAX);
  if (*basicvars.current == ':') basicvars.current++;	/* Skip ':' */
  if (*basicvars.current == NUL) {	/* Token is at end of line */
    basicvars.current++;		/* Move to start of next line */
    if (basicvars.traces.lines) trace_line(get_lineno(basicvars.current));
    basicvars.current = FIND_EXEC(basicvars.current);
  }
}

/*
** 'exec_endproc' deals with returns from procedures.
** The stack layout at this point should be:
**	<stuff to chuck away> <local vars> <return block> <arguments>
** Everything here has to be discarded.
*/
void exec_endproc(void) {
  fnprocinfo returnblock;
  if (basicvars.procstack == NIL) error(ERR_ENDPROC);	/* ENDPROC found outside a PROC */
  if (GET_TOPITEM != STACK_PROC) empty_stack(STACK_PROC);	/* Throw away unwanted entries on Basic stack */
  returnblock = pop_proc();	/* Fetch return address and so forth */
  if (returnblock.parmcount != 0) restore_parameters(returnblock.parmcount);	/* Procedure had parameters - Restore old values */
  if (basicvars.traces.enabled) {
    if (basicvars.traces.procs) trace_proc(returnblock.fnprocname, FALSE);
    if (basicvars.traces.branches) trace_branch(basicvars.current, returnblock.retaddr);
  }
  basicvars.current = returnblock.retaddr;
}

/*
** 'exec_fnreturn' deals with function returns.
** One unfortunate point is that if the result is a string and the string
** came from a variable, that is, the type is STACK_STRING, it is necessary
** to make a copy of the string in case the string came from a local
** variable. The reason for this is that the local variable will be
** destroyed when the function returns and the string returned to the
** heap
*/
void exec_fnreturn(void) {
  stackitem resultype;
  int32 intresult = 0;
  static float64 fpresult;
  basicstring stresult = {0, NULL};
  char *sp;
  fnprocinfo returnblock;
  if (basicvars.procstack == NIL) error(ERR_FNRETURN);	/* '=<expr>' found outside a FN */
  basicvars.current++;
  expression();
  resultype = GET_TOPITEM;
  if (resultype == STACK_INT)	/* Pop result from stack and ensure type is legal */
    intresult = pop_int();
  else if (resultype == STACK_FLOAT)
    fpresult = pop_float();
  else if (resultype == STACK_STRING) {	/* Have to make a copy of the string for safety */
    stresult = pop_string();
    sp = alloc_string(stresult.stringlen);
    if (stresult.stringlen != 0) memmove(sp, stresult.stringaddr, stresult.stringlen);
    stresult.stringaddr = sp;
    resultype = STACK_STRTEMP;
  }
  else if (resultype == STACK_STRTEMP)
    stresult = pop_string();
  else {
    error(ERR_VARNUMSTR);
  }
  empty_stack(STACK_FN);	/* Throw away unwanted entries on Basic stack */
  returnblock = pop_fn();	/* Fetch return address and so forth */
  if (returnblock.parmcount != 0) restore_parameters(returnblock.parmcount);	/* Procedure had arguments - restore old values */
  if (resultype == STACK_INT) {	/* Lastly, put the result back on the stack */
    PUSH_INT(intresult);
  }
  else if (resultype == STACK_FLOAT) {
    PUSH_FLOAT(fpresult);
  }
  else if (resultype == STACK_STRING) {
    PUSH_STRING(stresult);
  }
  else if (resultype == STACK_STRTEMP) {
    push_strtemp(stresult.stringlen, stresult.stringaddr);
  }
  if (basicvars.traces.enabled) {
    if (basicvars.traces.procs) trace_proc(returnblock.fnprocname, FALSE);
    if (basicvars.traces.branches) trace_branch(basicvars.current, returnblock.retaddr);
  }
  basicvars.current = returnblock.retaddr;
}

/*
** 'exec_endwhile' deals with the ENDWHILE statement. It is in fact
** more important than the 'WHILE' in that whether to continue with
** the loop or to simply move on to the next statement is decided here.
**
** One point to note is that Basic V allows loops to be nested
** incorrectly in that if one loop is not terminated within another,
** the inner one is automatically terminated by the outer one, for
** example:
**    WHILE X%<10
**      REPEAT ...
**    ENDWHILE
** Here, the 'REPEAT' loop is automatically terminated when then
** 'ENDWHILE' is reached. The code mimics this behaviour (in
** 'get_while').
*/
void exec_endwhile(void) {
  byte *tp;
  stack_while *wp;
  int32 result = 0;
  tp = basicvars.current+1;
  if (!ateol[*tp]) error(ERR_SYNTAX);
  if (GET_TOPITEM == STACK_WHILE) 	/* WHILE control block is top of stack */
    wp = basicvars.stacktop.whilesp;
  else {	/* Discard contents of stack as far as WHILE block */
    wp = get_while();
  }
  if (wp == NIL) error(ERR_NOTWHILE);	/* Not in a WHILE loop */
  if (basicvars.escape) error(ERR_ESCAPE);
  basicvars.current = wp->whilexpr;
  expression();
  if (GET_TOPITEM == STACK_INT)
    result = pop_int();
  else if (GET_TOPITEM == STACK_FLOAT)
    result = TOINT(pop_float());
  else {
    error(ERR_TYPENUM);
  }
  if (result != BASFALSE) {	/* Condition still true - Continue with loop */
    if (basicvars.traces.branches) trace_branch(tp, wp->whileaddr);
    basicvars.current = wp->whileaddr;
  }
  else {	/* Escape from loop - Remove WHILE control block from stack */
    pop_while();
    if (*tp == ':') tp++;		/* Continue at next token after ENDWHILE */
    if (*tp == NUL) {
      tp++;		/* Move to the start of the next line */
      if (basicvars.traces.lines) trace_line(get_lineno(tp));
      tp = FIND_EXEC(tp);	/* Skip to start of the executable tokens */
    }
    basicvars.current = tp;
  }
}

/*
** 'exec_error' deals with the 'ERROR' statement, which halts a
** program with a user-defined error.
** Note that the 'ERROR EXT' statement is not supported yet
*/
void exec_error(void) {
  int32 errnumber;
  stackitem stringtype;
  basicstring descriptor;
  char *errtext;
  basicvars.current++;	/* Skip the ERROR token*/
  errnumber = eval_integer();
  if (*basicvars.current != ',') error(ERR_COMISS);	/* Comma missing */
  basicvars.current++;
  expression();
  check_ateol();
  stringtype = GET_TOPITEM;
  if (stringtype != STACK_STRING && stringtype != STACK_STRTEMP) error(ERR_TYPESTR);
  descriptor = pop_string();
  errtext = tocstring(descriptor.stringaddr, descriptor.stringlen);
  if (stringtype == STACK_STRTEMP) free_string(descriptor);
  show_error(errnumber, errtext);	/* Report the error */
}

/*
** 'exec_for' deals with the 'FOR' statement at the start of a 'FOR' loop.
** It sets up the control block needed and starts the loop but that is all.
** Everything else is done by the 'NEXT' statement code.
*/
void exec_for(void) {
  boolean isinteger;
  lvalue forvar;
  int32 intlimit = 0, intstep = 0;
  static float64 floatlimit, floatstep;
  basicvars.current++;	/* Skip the 'FOR' token */
  get_lvalue(&forvar);
  if ((forvar.typeinfo & VAR_ARRAY) != 0 || (forvar.typeinfo & TYPEMASK)>VAR_FLOAT) {
    error(ERR_VARNUM);	/* Numeric variable required */
  }
  isinteger = (forvar.typeinfo & TYPEMASK)<VAR_FLOAT;
  if (*basicvars.current != '=') error(ERR_EQMISS);	/* '=' is missing */
  basicvars.current++;
  expression();		/* Get the control variable's initial value */
  if (*basicvars.current != TOKEN_TO) error(ERR_TOMISS);
  basicvars.current++;
  switch (forvar.typeinfo) {	/* Assign control variable's initial value */
  case VAR_INTWORD:
    switch (GET_TOPITEM) {
    case STACK_INT:
      *forvar.address.intaddr = pop_int();
      break;
    case STACK_FLOAT:
      *forvar.address.intaddr = TOINT(pop_float());
      break;
    default:
      error(ERR_TYPENUM);	/* Numeric value required for control variable initial value */
    }
    break;
  case VAR_FLOAT:
    switch (GET_TOPITEM) {
    case STACK_INT:
      *forvar.address.floataddr = TOFLOAT(pop_int());
      break;
    case STACK_FLOAT:
      *forvar.address.floataddr = pop_float();
      break;
    default:
      error(ERR_TYPENUM);	/* Numeric value required for control variable initial value */
    }
    break;
  case VAR_INTBYTEPTR:
    check_write(forvar.address.offset, sizeof(byte));
    switch (GET_TOPITEM) {
    case STACK_INT:
      basicvars.offbase[forvar.address.offset] = pop_int();
      break;
    case STACK_FLOAT:
      basicvars.offbase[forvar.address.offset] = TOINT(pop_float());
      break;
    default:
      error(ERR_TYPENUM);	/* Numeric value required for control variable initial value */
    }
    break;
  case VAR_INTWORDPTR:
    switch (GET_TOPITEM) {
    case STACK_INT:
      store_integer(forvar.address.offset, pop_int());
      break;
    case STACK_FLOAT:
      store_integer(forvar.address.offset, TOINT(pop_float()));
      break;
    default:
      error(ERR_TYPENUM);	/* Numeric value required for control variable initial value */
    }
    break;
  case VAR_FLOATPTR:
    switch (GET_TOPITEM) {
    case STACK_INT:
      store_float(forvar.address.offset, TOFLOAT(pop_int()));
      break;
    case STACK_FLOAT:
      store_float(forvar.address.offset, pop_float());
      break;
    default:
      error(ERR_TYPENUM);	/* Numeric value required for control variable initial value */
    }
    break;
  default:
    error(ERR_BROKEN, __LINE__, "mainstate");		/* Bad variable type found */
  }

/* Now evaluate the control variable's final value */

  expression();
  if (isinteger) {	/* Loop is an integer loop */
    if (GET_TOPITEM == STACK_INT)
      intlimit = pop_int();
    else if (GET_TOPITEM == STACK_FLOAT)
      intlimit = TOINT(pop_float());
    else {
      error(ERR_TYPENUM);		/* Numeric value required for final value */
    }
  }
  else {	/* Loop is a floating point loop */
    if (GET_TOPITEM == STACK_INT)
      floatlimit = TOFLOAT(pop_int());
    else if (GET_TOPITEM == STACK_FLOAT)
      floatlimit = pop_float();
    else {
      error(ERR_TYPENUM);		/* Numeric value required for final value */
    }
  }
  if (*basicvars.current == TOKEN_STEP) {
    basicvars.current++;
    expression();
    if (isinteger) {	/* Loop is an integer loop */
      if (GET_TOPITEM == STACK_INT)
        intstep = pop_int();
      else if (GET_TOPITEM == STACK_FLOAT)
        intstep = TOINT(pop_float());
      else {
        error(ERR_TYPENUM);		/* Numeric value required for step value */
      }
      if (intstep == 0) error(ERR_SILLY);
    }
    else {	/* Loop is a floating point loop */
      if (GET_TOPITEM == STACK_INT)
        floatstep = TOFLOAT(pop_int());
      else if (GET_TOPITEM == STACK_FLOAT)
        floatstep = pop_float();
      else {
        error(ERR_TYPENUM);		/* Numeric value required for step */
      }
      if (floatstep == 0.0) error(ERR_SILLY);
    }
  }
  else {	/* STEP not specified */
    if (isinteger)
      intstep = 1;
    else {
      floatstep = 1.0;
    }
  }
  if (!ateol[*basicvars.current]) error(ERR_SYNTAX);		/* Ensure there is nothing left on the line */
  if (*basicvars.current == ':') basicvars.current++;	/* Find the start of the statements in the loop */
  if (*basicvars.current == NUL) {	/* Not on this line - Try the next */
    basicvars.current++;
    if (basicvars.traces.lines) trace_line(get_lineno(basicvars.current));
    basicvars.current = FIND_EXEC(basicvars.current);
  }
  if (isinteger) {	/* Finally, set up the loop control block on the stack and end */
    boolean simple = forvar.typeinfo == VAR_INTWORD && intstep == 1;
    push_intfor(forvar, basicvars.current, intlimit, intstep, simple);
  }
  else {
    push_floatfor(forvar, basicvars.current, floatlimit, floatstep, FALSE);
  }
}

/*
** 'set_linedest' is called to locate the line to which a line number refers
** and fill in its address in the 'TOKEN_LINENUM' token. The address stored
** is that of the first token on the destination line. It returns a pointer
** to that token
*/
static byte *set_linedest(byte *tp) {
  int32 line;
  byte *dest;
  line = get_linenum(tp);
  dest = find_line(line);	/* Find the line refered to */
  if (get_lineno(dest) != line) error(ERR_LINEMISS, line);
  dest = FIND_EXEC(dest);	/* Find the first executable token */
  *tp = TOKEN_LINENUM;
  set_address(tp, dest);
  return dest;
}

/*
** 'exec_gosub' deals with the Basic 'GOSUB' statement
*/
void exec_gosub(void) {
  byte *dest = NULL;
  int32 line;
  if (basicvars.escape) error(ERR_ESCAPE);
  basicvars.current++;		/* Slip GOSUB token */
  if (*basicvars.current == TOKEN_LINENUM) {
    dest = GET_ADDRESS(basicvars.current, byte *);
    basicvars.current+=1+LOFFSIZE;	/* Skip 'line number' token */
  }
  else if (*basicvars.current == TOKEN_XLINENUM) {	/* GOSUB destination not filled in yet */
    dest = set_linedest(basicvars.current);
    basicvars.current+=1+LOFFSIZE;	/* Skip 'line number' token */
  }
  else if (*basicvars.current == '(') {	/* Destination line number is given by an expression */
    line = eval_intfactor();
    dest = find_line(line);	/* Find start of destination line */
    if (get_lineno(dest) != line) error(ERR_LINEMISS, line);
    dest = FIND_EXEC(dest);		/* Move from start of line to first token */
  }
  else {
    error(ERR_SYNTAX);
  }
  check_ateol();
  push_gosub();
  if (basicvars.traces.branches) trace_branch(basicvars.current, dest);
  basicvars.current = dest;
}

/*
** 'exec_goto' handles the Basic 'GOTO' statement
*/
void exec_goto(void) {
  byte *dest = NULL;
  int32 line = 0;
  if (basicvars.escape) error(ERR_ESCAPE);
  basicvars.current++;		/* Skip 'GOTO' token */
  if (*basicvars.current == TOKEN_LINENUM) {
    dest = GET_ADDRESS(basicvars.current, byte *);
    basicvars.current+=1+LOFFSIZE;	/* Skip 'line number' token */
  }
  else if (*basicvars.current == TOKEN_XLINENUM) {	/* GOTO destination not filled in yet */
    dest = set_linedest(basicvars.current);
    basicvars.current+=1+LOFFSIZE;	/* Skip 'line number' token */
  }
  else if (*basicvars.current == '(') {	/* Destination line number is given by an expression */
    line = eval_intfactor();
    if (line<0 || line>MAXLINENO) error(ERR_LINENO);	/* Line number is out of range */
    dest = find_line(line);
    if (get_lineno(dest) != line) error(ERR_LINEMISS, line);
    dest = FIND_EXEC(dest);
  }
  else {	/* Anything else is an error */
    error(ERR_SYNTAX);
  }
  check_ateol();
  if (basicvars.traces.branches) trace_branch(basicvars.current, dest);
  basicvars.current = dest;
}

/*
** 'exec_blockif' is called to handle block 'IF' statements.
** The layout of an 'IF' statement is:
**   <IF token> <offset of THEN part> <offset of ELSE part> <expression> ...
*/
void exec_blockif(void) {
  byte *dest;
  dest = basicvars.current+1;		/* Point at the 'THEN' offset */
  basicvars.current+=1+2*OFFSIZE;	/* Skip IF token and THEN and ELSE offsets */
  expression();
  if (GET_TOPITEM == STACK_INT) {
    if (pop_int() == BASFALSE) dest+=OFFSIZE;	/* Cond was false - Point at offset to 'ELSE' part */
  }
  else if (GET_TOPITEM == STACK_FLOAT) {
    if (TOINT(pop_float()) == BASFALSE) dest+=OFFSIZE;	/* Point at offset to 'ELSE' part */
  }
  else {
    error(ERR_TYPENUM);
  }
  if (basicvars.traces.enabled) {	/* Branch after dealing with debug info */
    if (basicvars.traces.lines) trace_line(get_lineno(find_linestart(GET_DEST(dest))));
    if (basicvars.traces.branches) trace_branch(dest, GET_DEST(dest));
  }
  basicvars.current = GET_DEST(dest);		/* Branch to the 'THEN' or 'ELSE' code */
}

/*
** 'exec_singlif' is called to deal with single line 'IF' statements
*/
void exec_singlif(void) {
  byte *dest, *here;
  here = dest = basicvars.current+1;	/* Point at the 'THEN' offset */
  basicvars.current+=1+2*OFFSIZE;	/* Skip IF token and THEN and ELSE offsets */
  expression();
  if (GET_TOPITEM == STACK_INT) {
    if (pop_int() == BASFALSE) dest+=OFFSIZE;	/* Cond was false - Point at offset to 'ELSE' part */
  }
  else if (GET_TOPITEM == STACK_FLOAT) {
    if (TOINT(pop_float()) == BASFALSE) dest+=OFFSIZE;	/* Point at offset to 'ELSE' part */
  }
  else {
    error(ERR_TYPENUM);
  }
  dest = GET_DEST(dest);	/* Find code after the 'THEN' or 'ELSE' */
  if (*dest == TOKEN_LINENUM)	/* There is a line number there */
    dest = GET_ADDRESS(dest, byte *);
  else if (*dest == TOKEN_XLINENUM) {	/* Address of line is not filled in */
    dest = set_linedest(dest);	/* Find line and fill in its address */
  }
  if (basicvars.traces.enabled) {	/* Deal with any trace info needed */
    if (basicvars.traces.lines) {
      int32 destline = get_lineno(find_linestart(dest));
      if (get_lineno(here) != destline) trace_line(destline);
    }
    if (basicvars.traces.branches) trace_branch(here, dest);
  }
  basicvars.current = dest;
}

/*
** 'exec_xif' is called the first time an 'IF' statement is encountered
** to identify the type of 'IF' and to fill in the offsets to the
** 'THEN' and 'ELSE' parts of the statement.
*/
void exec_xif(void) {
  byte *lp2 = NULL, *dest, *ifplace, *thenplace, *elseplace;
  int32 result = 0;
  boolean single;
  ifplace = basicvars.current; 		/* Set up a pointer to the 'IF' token */
  thenplace = ifplace+1;		/* Set up addresses where offsets will be stored */
  elseplace = ifplace+1+OFFSIZE;
  basicvars.current+=1+2*OFFSIZE;
  expression();
  if (GET_TOPITEM == STACK_INT)
    result = pop_int();
  else if (GET_TOPITEM == STACK_FLOAT)
    result = TOINT(pop_float());
  else {
    error(ERR_TYPENUM);
  }
  single = *basicvars.current != TOKEN_THEN;	/* No 'THEN' = single line if */
  if (*basicvars.current == TOKEN_THEN) {
    lp2 = basicvars.current+1;	/* Skip the 'THEN' and see if it is the last item on the line */
    single = *lp2 != NUL;		/* A 'null' here means that this is the start of a block 'IF' */
  }
  if (single) {		/* Dealing with a single line 'IF' */
    *ifplace = TOKEN_SINGLIF;
    if (*basicvars.current == TOKEN_XELSE) {	/* Got 'IF <expression> ELSE ...' i.e. there is no 'THEN' part */
      lp2 = basicvars.current+1+OFFSIZE;	/* Find the token after the 'ELSE' */
      set_dest(elseplace, lp2);
      while (*lp2 != NUL) lp2 = skip_token(lp2);		/* Find next line for dummy 'THEN' part */
      lp2++;	/* Move to the start of the next line */
      set_dest(thenplace, FIND_EXEC(lp2));
    }
    else {
/*
** There are two cases to deal with here:
** 1)  Statement has a 'THEN'
** 2)  Statement omits the 'THEN'
** In the first case, 'lp2' already points at the first token after the
** 'THEN'. If the 'THEN' is missing, 'basicvars.current' points at the token
** of interest. Once the 'THEN' part has been dealt with, the 'ELSE' has to
** be found. Of course, there might not be an 'ELSE' in which case the 'ELSE'
** offset just points at the next line
*/
      if (*basicvars.current != TOKEN_THEN) lp2 = basicvars.current;
      set_dest(thenplace, lp2);
      while (*lp2 != NUL && *lp2 != TOKEN_XELSE) lp2 = skip_token(lp2);
      if (*lp2 == TOKEN_XELSE) lp2+=1+OFFSIZE;	/* Find the token after the 'ELSE' */
      if (*lp2 == NUL) {	/* Find the first token on the next line */
        lp2++;
        lp2 = FIND_EXEC(lp2);
      }
      set_dest(elseplace, lp2);
    }
  }
  else {	/* Dealing with a block 'IF' */
    int32 depth;
    *ifplace = TOKEN_BLOCKIF;
/*
** Now find the 'ELSE' or 'ENDIF' that matches this 'IF' to fill in the
** 'ELSE' offset. A couple of points to note here:
** 1) lp2 points at the NULL after the 'THEN' token here
** 2) If no 'ELSE' or 'ENDIF' is found then it depends whether the result
**    of the 'IF' expression is true or false whether or not this is
**    flagged as an error. If it is false then it is a syntax error.
**    If true the error is ignored.
*/
    basicvars.current = lp2+1;		/* Move to the start of the next line */
    set_dest(thenplace, FIND_EXEC(basicvars.current));
    depth = 1;
    while (depth>0) {	/* Look for an ELSE or ENDIF */
      if (AT_PROGEND(basicvars.current)) {
        if (result == BASFALSE)
          error(ERR_ENDIF);	/* Result is 'false' but no ELSE or ENDIF found */
        else {	/* Otherwise we pretend we have found the end of the block IF */
          break;
        }
      }
      lp2 = FIND_EXEC(basicvars.current);	/* Find the first executable token */
      if (*lp2 == TOKEN_ENDIF)
        depth--;
      else if (*lp2 == TOKEN_XLHELSE) {
        if (depth == 1) depth = 0;	/* ELSE can only decrement depth if at top level of nest */
      }
      else if (start_blockif(lp2)) {	/* There is a block IF nested here */
        depth++;
      }
      if (depth>0) basicvars.current+=GET_LINELEN(basicvars.current);
    }
    if (AT_PROGEND(basicvars.current))		/* No 'ELSE' or 'ENDIF' found */
      lp2 = FIND_EXEC(basicvars.current);	/* Fake an address for the 'ELSE' code */
    else {	/* ELSE or ENDIF found */
      if (*lp2 == TOKEN_XLHELSE)	/* Move past ELSE and offset */
        lp2+=1+OFFSIZE;
      else {	/* Move past ENDIF */
        lp2++;
      }
      if (*lp2 == NUL) {	/* There is nothing else on the line - Skip to next line */
        lp2++;
        lp2 = FIND_EXEC(lp2);
      }
    }
    set_dest(elseplace, lp2);
  }
/*
** Finally, execute the 'IF' statement. The 'IF' expression has had to be
** evalued in order to see what followed it so the action of the statement
** has to be carried out here rather than calling one of the other 'IF'
** functions
*/
  if (result != BASFALSE)
    dest = GET_DEST(thenplace);	/* Result is 'true' - Go to 'THEN' code */
  else {
    dest = GET_DEST(elseplace);
  }
  if (single) {
    if (*dest == TOKEN_XLINENUM)	/* Unresolved line number follows THEN or ELSE */
      dest = set_linedest(dest);
    else if (*dest == TOKEN_LINENUM) {	/* Resolved line number follows THEN or ELSE */
      dest = GET_ADDRESS(dest, byte *);
    }
  }
  if (basicvars.traces.lines) {
    int32 destline = get_lineno(find_linestart(dest));
    if (get_lineno(basicvars.current) != destline) trace_line(destline);
  }
  if (basicvars.traces.branches) trace_branch(ifplace, dest);
  basicvars.current = dest;
}

/*
** 'exec_library' deals with the Basic 'LIBRARY' statement.
** This version allows a list of library names to be specified
** after the keyword 'LIBRARY'
*/
void exec_library(void) {
  stackitem stringtype;
  basicstring name;
  char *libname;
  basicvars.current++;
  if (*basicvars.current == TOKEN_LOCAL) error(ERR_NOLIBLOC);	/* 'LIBRARY LOCAL' not allowed */
  do {
    expression();	/* Get a library name */
    stringtype = GET_TOPITEM;
    if (stringtype != STACK_STRING && stringtype != STACK_STRTEMP) error(ERR_TYPESTR);
    name = pop_string();
    if (name.stringlen>0) {	/* Ignore non-existant library names */
      libname = tocstring(name.stringaddr, name.stringlen);
      if (stringtype == STACK_STRTEMP) free_string(name);
      read_library(libname, LOAD_LIBRARY);	/* Save library on Basic heap */
    }
    if (*basicvars.current != ',') break;		/* Escape if there is nothing more to do */
    basicvars.current++;
  } while (TRUE);
  check_ateol();
}

/*
** 'def_locvar' handles the 'LOCAL <variable>' statement and
** creates local variables. If the variable already exists it
** just its value on the stack and resets the variable to zero.
** If it does not exist, a new variable is created.
*/
static void def_locvar(void) {
  basicstring descriptor;
  lvalue locvar;
  if (basicvars.procstack == NIL) error(ERR_LOCAL);	/* LOCAL found outside a PROC or FN */
  basicvars.runflags.make_array = TRUE;	/* Create arrays, do not flag errors if missing in 'get_lvalue' */
  do {
    get_lvalue(&locvar);
    switch (locvar.typeinfo) {	/* Now to save the variable and set it to its new initial value */
    case VAR_INTWORD:
      save_int(locvar, *locvar.address.intaddr);
      *locvar.address.intaddr = 0;
      break;
    case VAR_FLOAT:
      save_float(locvar, *locvar.address.floataddr);
      *locvar.address.floataddr = 0.0;
      break;
    case VAR_STRINGDOL:
      save_string(locvar, *locvar.address.straddr);
      locvar.address.straddr->stringlen = 0;
      locvar.address.straddr->stringaddr = nullstring;	/* 'nullstring' is defined in variables */
      break;
    case VAR_INTBYTEPTR:
      check_write(locvar.address.offset, sizeof(byte));
      save_int(locvar, basicvars.offbase[locvar.address.offset]);
      basicvars.offbase[locvar.address.offset] = 0;
      break;
    case VAR_INTWORDPTR:
      save_int(locvar, get_integer(locvar.address.offset));
      store_integer(locvar.address.offset, 0);
      break;
    case VAR_FLOATPTR:
      save_float(locvar, get_float(locvar.address.offset));
      store_float(locvar.address.offset, 0.0);
      break;
    case VAR_DOLSTRPTR:
      check_write(locvar.address.offset, sizeof(byte));
      descriptor.stringlen = get_stringlen(locvar.address.offset)+1;	/* +1 for CR at end */
      descriptor.stringaddr = alloc_string(descriptor.stringlen);
      memmove(descriptor.stringaddr, &basicvars.offbase[locvar.address.offset], descriptor.stringlen);
      save_string(locvar, descriptor);
      basicvars.offbase[locvar.address.offset] = CR;
      break;
    case VAR_INTARRAY: case VAR_FLOATARRAY: case VAR_STRARRAY:
      save_array(locvar);
      *locvar.address.arrayaddr = NIL;
      break;
    default:
      error(ERR_BROKEN, __LINE__, "mainstate");	/* Just in case something gets clobbered */
    }
    if (*basicvars.current != ',') break;	/* Escape if there is nothing more to do */
    basicvars.current++;	/* Skip ',' token */
  } while(TRUE);
  basicvars.runflags.make_array = FALSE;
  check_ateol();
}

/*
** 'exec_local' deals with the Basic 'LOCAL' statement. There are three
** versions of this: 'LOCAL <variable>', 'LOCAL ERROR' and 'LOCAL DATA'
*/
void exec_local(void) {
  basicvars.current++;	/* Skip LOCAL token */
  switch (*basicvars.current) {
  case TOKEN_ERROR:	/* Got 'LOCAL ERROR' */
    basicvars.current = skip_token(basicvars.current);
    check_ateol();
    push_error(basicvars.error_handler);
    break;
  case TOKEN_DATA:	/* Got 'LOCAL DATA' */
    basicvars.current = skip_token(basicvars.current);
    check_ateol();
    push_data(basicvars.datacur);
    break;
  default:	/* Defining local variables */
    def_locvar();
  }
}

/*
** 'exec_next' handles what is really the business end of a 'FOR' loop.
*/
void exec_next(void) {
  stack_for *fp;
  lvalue nextvar;
  boolean contloop = FALSE;
  int32 intvalue;
  static float64 floatvalue;
  if (basicvars.escape) error(ERR_ESCAPE);
  do {
    if (GET_TOPITEM == STACK_INTFOR || GET_TOPITEM == STACK_FLOATFOR) /* FOR control block is top of stack */
      fp = basicvars.stacktop.forsp;
    else {	/* Discard entries until FOR control block is found */
       fp = get_for();
    }
    if (fp == NIL) error(ERR_NOTFOR);	/* Not in a FOR loop */
    basicvars.current++;	/* Skip NEXT token */
    if (!ateol[*basicvars.current]) {	/* There is a control variable (or two) here */
      if (*basicvars.current != ',') {
        get_lvalue(&nextvar);
        if (nextvar.address.intaddr != fp->forvar.address.intaddr) error(ERR_WRONGFOR);	/* Cannot match 'FOR' loop variable */
      }
    }
/*
** The 'simplefor' flag is set to true for the most common type of FOR loop,
** that is, the loop control variable is an integer variable and the step
** is +1. Deal with this case first and anything else later
*/
    if (fp->simplefor) {
      intvalue = *fp->forvar.address.intaddr+=1;
      if (intvalue<=fp->fortype.intfor.intlimit) {	/* Continue with loop */
        if (basicvars.traces.branches) trace_branch(basicvars.current, fp->foraddr);
        basicvars.current = fp->foraddr;
        return;
      }
      contloop = FALSE;	/* Escape from loop */
    }
    else {
      switch (fp->forvar.typeinfo) {	/* Right, let's bump up the 'FOR' variable */
      case VAR_INTWORD:		/* Word-aligned integer value */
        intvalue = *fp->forvar.address.intaddr+fp->fortype.intfor.intstep;
        *fp->forvar.address.intaddr = intvalue;
        if (fp->fortype.intfor.intstep>0)
          contloop = intvalue<=fp->fortype.intfor.intlimit;
        else {
          contloop = intvalue>=fp->fortype.intfor.intlimit;
        }
        break;
      case VAR_FLOAT:		/* Word-aligned floating point value */
        floatvalue = *fp->forvar.address.floataddr+fp->fortype.floatfor.floatstep;
        *fp->forvar.address.floataddr = floatvalue;
        if (fp->fortype.floatfor.floatstep>0)
          contloop = floatvalue<=fp->fortype.floatfor.floatlimit;
        else {
          contloop = floatvalue>=fp->fortype.floatfor.floatlimit;
        }
        break;
      case VAR_INTBYTEPTR:	/* Pointer to a byte-aligned byte-sized integer */
        intvalue = basicvars.offbase[fp->forvar.address.offset]+fp->fortype.intfor.intstep;
        basicvars.offbase[fp->forvar.address.offset] = intvalue;
        if (fp->fortype.intfor.intstep>0)
          contloop = intvalue<=fp->fortype.intfor.intlimit;
        else {
          contloop = intvalue>=fp->fortype.intfor.intlimit;
        }
        break;
      case VAR_INTWORDPTR:	/* Pointer to a byte-aligned word-sized integer */
        intvalue = get_integer(fp->forvar.address.offset)+fp->fortype.intfor.intstep;
        store_integer(fp->forvar.address.offset, intvalue);
        if (fp->fortype.intfor.intstep>0)
          contloop = intvalue<=fp->fortype.intfor.intlimit;
        else {
          contloop = intvalue>=fp->fortype.intfor.intlimit;
        }
        break;
      case VAR_FLOATPTR:	/* Pointer to byte-aligned floating point value */
        floatvalue = get_float(fp->forvar.address.offset)+fp->fortype.floatfor.floatstep;
        store_float(fp->forvar.address.offset, floatvalue);
        if (fp->fortype.floatfor.floatstep>0)
          contloop = floatvalue<=fp->fortype.floatfor.floatlimit;
        else {
          contloop = floatvalue>=fp->fortype.floatfor.floatlimit;
        }
        break;
      default:
        error(ERR_BROKEN, __LINE__, "mainstate");
      }
    }
    if (contloop) {	/* Continue with loop */
      if (basicvars.traces.branches) trace_branch(basicvars.current, fp->foraddr);
      basicvars.current = fp->foraddr;
      return;
    }
    pop_for();	/* Loop has finished - Discard loop control block */
  } while (*basicvars.current == ',');
  check_ateol();
}

/*
** 'exec_onerror' deals with the Basic 'ON ERROR' statement
*/
static void exec_onerror(void) {
  basicvars.current++;		/* Skip ON token */
  switch (*basicvars.current) {
  case TOKEN_OFF:	/* Got 'ON ERROR OFF' */
    clear_error();
    basicvars.current++;
    check_ateol();
    break;
  case TOKEN_LOCAL:	/* Got 'ON ERROR LOCAL' */
    basicvars.current++;
    set_local_error();
    while (*basicvars.current != NUL) basicvars.current = skip_token(basicvars.current);
    break;
  default: /* Got 'ON ERROR <statements>' */
    set_error();
    while (*basicvars.current != NUL) basicvars.current = skip_token(basicvars.current);
  }
}

/*
** 'find_else' is called to locate an 'ELSE' clause in a 'ON' statement.
** If it finds one, control is passed to the statement after the 'ELSE'
** otherwise an error is flagged.
**'ateol' checks for both an end of line and an 'ELSE' so it is used here.
** Note that the code does not check the syntax of the statement along the
** way. All it is interested in is finding an 'ELSE' (this matches what the
** Acorn interpreter does).
*/
static void find_else(byte *tp, int32 index) {
  while (!ateol[*tp]) tp = skip_token(tp);
  if (*tp == TOKEN_XELSE) {
    if (basicvars.traces.branches) trace_branch(basicvars.current, tp);
/*
** Note that the 'ELSE' token is followed by an offset. Need to
** skip this as well
*/
    basicvars.current = tp+1+OFFSIZE;
  }
  else {	/* No 'ELSE' clause found - Flag an 'ON' range error */
    error(ERR_ONRANGE, index);
  }
}

/*
** 'find_onentry' looks for entry number 'wanted' in an 'ON' statement.
** It returns a pointer to the 'wanted'th item or the 'ELSE' token of
** an 'ELSE' clause if no entry is found. If there is no entry to match
** the value passed to it and no 'ELSE' clause, an error is flagged.
** The function takes into account any expressions in brackets it comes
** across. These could be procedure or function calls or array references.
** ('ON' statements allow general expressions instead of just simple line
** numbers.)
*/
static byte *find_onentry(byte *tp, int32 wanted) {
  int32 brackets, count;
  count = 1;
  brackets = 0;
  do {
    while (*tp != ':' && *tp != NUL && *tp != TOKEN_XELSE && (*tp != ',' || brackets != 0)) {
      tp = skip_token(tp);
      if (*tp == '(')
        brackets++;
      else if (*tp == ')') {
        brackets--;
      }
    }
    if (*tp == TOKEN_XELSE) break;	/* Check this first to avoid clash with ATEOL */
    if (ateol[*tp]) error(ERR_ONRANGE, wanted);
    count++;
    if (count == wanted) break;
    if (*tp != ',') error(ERR_COMISS);
    tp++;	/* Skip the ',' */
  } while (TRUE);
  if (*tp == ',') tp++;
  return tp;
}

/*
** 'exec_onbranch' handles the 'ON ... GOTO', 'ON ... GOSUB' and 'ON ... PROC'
** statements.
** This code is strictly interpreted. It would be better if a table of
** pointers to the line numbers was constructed to allow the statement to be
** processed more quickly but this code will do for now. The 'ON' statement
** is not that important in Basic V and is mainly here for compatibility
*/
static void exec_onbranch(void) {
  int32 index;
  byte onwhat;
  index = eval_integer();
  if (index<1)	/* 'ON' index is out of range */
    find_else(basicvars.current, index);
  else {
    onwhat = *basicvars.current;
    if (onwhat == TOKEN_GOTO || onwhat == TOKEN_GOSUB) {
      int32 line;
      byte *dest;
      basicvars.current++;	/* Skip the 'GOTO' or 'GOSUB' token */
      if (index>1) basicvars.current = find_onentry(basicvars.current, index);
      if (*basicvars.current == TOKEN_XELSE) {
        basicvars.current+=1+OFFSIZE;	/* Find statement after 'ELSE' */
        if (*basicvars.current == TOKEN_XLINENUM) error(ERR_SYNTAX);	/* Line number is not allowed here */
      }
      else {	/* Try to find a line number */
        if (*basicvars.current == TOKEN_LINENUM)		/* GOTO/GOSUB destination is known */
          dest = GET_ADDRESS(basicvars.current, byte *);
        else if (*basicvars.current == TOKEN_XLINENUM)	/* GOTO/GOSUB destination not filled in yet */
          dest = set_linedest(basicvars.current);
        else {	/* Destination line number is given by an expression */
	  line = eval_integer();
          if (line<0 || line>MAXLINENO) error(ERR_LINENO);	/* Line number is out of range */
          dest = find_line(line);
          if (get_lineno(dest) != line) error(ERR_LINEMISS, line);
          dest = FIND_EXEC(dest);
        }
        if (basicvars.traces.branches) trace_branch(basicvars.current, dest);
        if (onwhat == TOKEN_GOSUB) {	/* Got 'ON ... GUSUB'. Find point to which to return */
          while (*basicvars.current != ':' && *basicvars.current != NUL) basicvars.current = skip_token(basicvars.current);
          if (*basicvars.current == ':') basicvars.current++;
          push_gosub();
        }
        basicvars.current = dest;
      }
    }
    else if (onwhat == TOKEN_XFNPROCALL || onwhat == TOKEN_FNPROCALL) {	/* Got 'ON ... PROC' */
      byte *base;
      fnprocdef *dp = NULL;
      variable *pp = NULL;
      if (index>1) basicvars.current = find_onentry(basicvars.current, index);
      if (*basicvars.current == TOKEN_XELSE) {	/* Branch to statement after 'ELSE' */
        basicvars.current+=1+OFFSIZE;		/* Find statement after 'ELSE' */
        if (*basicvars.current == TOKEN_XLINENUM) error(ERR_SYNTAX);	/* Line number is not allowed here */
      }
      else {	/* Call one of the procedures */
        if (*basicvars.current == TOKEN_XFNPROCALL) {	/* Procedure call not seen before */
          byte *ep;
          base = get_srcaddr(basicvars.current);	/* Find the start of the procedure name */
          ep = skip_name(base);
          if (*(ep-1) == '(') ep--;	/* Do not include '(' of parameter list in name */
          pp = find_fnproc(base, ep-base);
          dp = pp->varentry.varfnproc;
          set_address(basicvars.current, pp);
          *basicvars.current = TOKEN_FNPROCALL;
          basicvars.current+=1+LOFFSIZE;		/* Skip pointer to procedure */
          if (*basicvars.current != '(') {	/* PROC call has no parameters */
            if (dp->parmlist != NIL) error(ERR_NOTENUFF, pp->varname);	/* But it should have */
          }
          else if (dp->parmlist == NIL) {		/* Got a '(' but PROC/FN has no parameters */
            error(ERR_TOOMANY, pp->varname);
          }
        }
        else if (*basicvars.current == TOKEN_FNPROCALL) {	/* Known procedure */
          pp = GET_ADDRESS(basicvars.current, variable *);
          dp = pp->varentry.varfnproc;
          basicvars.current+=1+LOFFSIZE;		/* Skip pointer to procedure */
        }
        else {
          error(ERR_SYNTAX);
        }
        if (*basicvars.current == '(') push_parameters(dp, pp->varname);	/* Deal with parameters */
        if (basicvars.traces.enabled) {
          if (basicvars.traces.procs) trace_proc(pp->varname, TRUE);
          if (basicvars.traces.branches) trace_branch(basicvars.current, dp->fnprocaddr);
        }
        while (*basicvars.current != ':' && *basicvars.current != NUL) basicvars.current = skip_token(basicvars.current);	/* Find return address */
        if (*basicvars.current == ':') basicvars.current++;
        push_proc(pp->varname, dp->parmcount);
        basicvars.current = dp->fnprocaddr;
      }
    }
    else {
      error(ERR_SYNTAX);
    }
  }
}

/*
** 'exec_on' deals with the various types of 'ON' statement
*/
void exec_on(void) {
  basicvars.current++;	/* Skip ON token */
  if (*basicvars.current == TOKEN_ERROR)	/* Dealing with 'ON ERROR' */
    exec_onerror();
  else if (ateol[*basicvars.current])	/* Got just 'ON' */
    emulate_on();
  else {
    exec_onbranch();
  }
}

/*
** 'exec_oscli' issues an OS command.
** The interpreter supports and extended 'OSCLI ... TO' version of
** the statement which allows command responses to be read
*/
void exec_oscli(void) {
  stackitem stringtype;
  basicstring descriptor;
  lvalue response, linecount;
  boolean tofile;
  char respname[FNAMESIZE];
  int length, count, n;
  FILE *respfile;
  char *p;
  basicarray *ap;
  basicvars.current++;	/* Hop over the OSCLI token */
  expression();
  stringtype = GET_TOPITEM;
  if (stringtype != STACK_STRING && stringtype != STACK_STRTEMP) error(ERR_TYPESTR);
  tofile = *basicvars.current == TOKEN_TO;
  if (tofile) {	/* Have got 'OSCLI <command> TO' */
    basicvars.current++;
    get_lvalue(&response);
    if (response.typeinfo != VAR_STRARRAY) error(ERR_STRARRAY);
    if (*basicvars.current == ',') {	/* Variable in which to store count of lines read */
      basicvars.current++;
      get_lvalue(&linecount);
    }
    else {
      linecount.typeinfo = 0;
    }
  }
  check_ateol();
  descriptor = pop_string();
  memmove(basicvars.stringwork, descriptor.stringaddr, descriptor.stringlen);	/* Copy string */
  basicvars.stringwork[descriptor.stringlen] = NUL;		/* Append a NUL keep OS_CLI happy */
  if (stringtype == STACK_STRTEMP) free_string(descriptor);
/* Issue command */
  if (!tofile) {	/* Response not wanted - Run command and go home */
    emulate_oscli(basicvars.stringwork, NIL);
    return;
  }
/*
** Issue the command and then read the command response
*/
  if (!secure_tmpnam(respname)) {
    error (ERR_OSCLIFAIL, strerror (errno));
    return;
  }
  emulate_oscli(basicvars.stringwork, respname);
  respfile = fopen(respname, "rb");
  if (respfile == 0) return;
  ap = *response.address.arrayaddr;
/* Start by discarding the current contents of the array */
  descriptor.stringlen = 0;
  descriptor.stringaddr = nullstring;	/* Found in variables.c */
  for (n=0; n<ap->arrsize; n++) {
    free_string(ap->arraystart.stringbase[n]);
    ap->arraystart.stringbase[n] = descriptor;
  }
  count = 0;	/* Number of lines read */
  while (!feof(respfile) && count+1<ap->arrsize) {	/* Read the command output */
    p = fgets(basicvars.stringwork, MAXSTRING, respfile);
    if (p == NIL) {	/* Either an error or EOF reached and no data read */
      if (!ferror(respfile)) break;		/* End of file and no data read */
      fclose(respfile);
      remove(respname);
      error(ERR_BROKEN, __LINE__, "mainstate");
    }
/* Remove any CRs or LFs or trailing blanks in the line and copy it to the string array */
    if (p == NIL) break;
    p = basicvars.stringwork;
    if (p[0] == '\r') p++;	/* Remove possible CR at the start of the line */
    length = strlen(p);
    while (length>0 && (p[length-1] == '\n' || p[length-1] == '\r' || p[length-1] == ' ')) length--;
    if (length>0 || !feof(respfile)) {	/* Don't want an empty line at the end of the array */
      descriptor.stringlen = length;
      descriptor.stringaddr = alloc_string(length);
      if (length>0) memmove(descriptor.stringaddr, p, length);
      count++;
      ap->arraystart.stringbase[count] = descriptor;
    }
  }
  fclose(respfile);
  remove(respname);
/* Save the number of lines stored in the array */
  if (linecount.typeinfo != 0) store_value(linecount, count, TRUE);
}

/*
** 'exec_overlay' deals with the unsupported 'OVERLAY' statement
*/
void exec_overlay(void) {
  error(ERR_UNSUPSTATE);
}

/*
** 'exec_proc' calls a procedure
*/
void exec_proc(void) {
  fnprocdef *dp;
  variable *vp;
  if (basicvars.escape) error(ERR_ESCAPE);
  vp = GET_ADDRESS(basicvars.current, variable *);
  dp = vp->varentry.varfnproc;
  basicvars.current+=1+LOFFSIZE;		/* Skip pointer to procedure */
  if (*basicvars.current == '(') {
    push_parameters(dp, vp->varname);	/* Deal with parameters */
    if (!ateol[*basicvars.current]) error(ERR_SYNTAX);
  }
  push_proc(vp->varname, dp->parmcount);
  if (basicvars.traces.enabled) {
    if (basicvars.traces.procs) trace_proc(vp->varname, TRUE);
    if (basicvars.traces.branches) trace_branch(basicvars.current, dp->fnprocaddr);
  }
  basicvars.current = dp->fnprocaddr;
}

/*
** 'exec_xproc' is invoked the first time a reference to a procedure is
** seen to locate the procedure and fill in its address
*/
void exec_xproc(void) {
  byte *tp, *base;
  variable *vp;
  fnprocdef *dp;
  tp = basicvars.current;
  base = get_srcaddr(tp);	/* Point at name of procedure */
  if (*base != TOKEN_PROC) error(ERR_NOTAPROC);	/* Ensure a procedure is being called */
  tp = skip_name(base);		/* Skip name */
  if (*(tp-1) == '(') tp--;	/* Do not include '(' of parameter list in name */
  vp = find_fnproc(base, tp-base);
  dp = vp->varentry.varfnproc;
  *basicvars.current = TOKEN_FNPROCALL;
  set_address(basicvars.current, vp);
  tp = basicvars.current+LOFFSIZE+1;
  if (*tp != '(') {	/* PROC call has no parameters */
    if (dp->parmlist != NIL) error(ERR_NOTENUFF, vp->varname);	/* But it should have */
    if (!ateol[*tp]) error(ERR_SYNTAX);		/* No parameters - Can check for end of statement here */
  }
  else if (dp->parmlist == NIL) {		/* Got a '(' but PROC/FN has no parameters */
    error(ERR_TOOMANY, vp->varname);
  }
  exec_proc();		/* Call the procedure */
}

/*
** 'exec_quit' finishes the run of the interpreter itself. It
** can be followed a return code. This value is passed back to
** the operating system. It defaults to 0 (EXIT_SUCCESS)
*/
void exec_quit(void) {
  int32 retcode;
  basicvars.current++;
  if (isateol(basicvars.current))	/* QUIT is not followed by anything */
    retcode = EXIT_SUCCESS;
  else {	/* QUIT is followed by a return code */
    retcode = eval_integer();
    check_ateol();
  }
  exit_interpreter(retcode);
}

/*
** 'find_data' is called to find the start of the next data field in a
** DATA statement.
** On entry, datacur, the data pointer, will either be NIL or pointing
** at a ',', the DATA token at the start of a line or the NUL at the end
** of the line.
*/
static void find_data(void) {
  byte *dp;
  dp = basicvars.datacur;
  if (dp != NIL && (*dp == ',' || *dp == TOKEN_DATA)) {	/* Skip to next field */
    basicvars.datacur++;
    return;
  }
  if (dp == NIL)		/* First READ of all */
    dp = basicvars.start;
  else {	/* At end of line - Skip to next one */
/* The 'end of the line' here is actually the end of the source */
/* part of the line. This is followed by the DATA token and the */
/* offset back to the start of the data itself. The code has to */
/* skip these items to move to the start of the next line */
    dp = skip_token(dp+1)+1;
  }
/* Look for the next 'DATA' statement */
  while (!AT_PROGEND(dp) && *FIND_EXEC(dp) != TOKEN_DATA) dp+=GET_LINELEN(dp);
  if (AT_PROGEND(dp)) error(ERR_DATA);	/* Have not found a DATA statement */
/*
** The DATA token is followed by the offset to the start of the data
** in the source part of the line. Find address of data
*/
  basicvars.datacur = get_srcaddr(FIND_EXEC(dp));
}

/*
** 'read_numeric' deals with numeric variables found in 'READ' statements.
** Here, the value in the 'DATA' statement is interpreted as an expression
** and not just a string. The data pointer is left pointing at the ','
** or NUL at the end of the line after the field
*/
static void read_numeric(lvalue destination) {
  byte *dp;
  stackitem itemtype;
  int32 n;
  char text[MAXSTATELEN];
  byte readexpr[MAXSTATELEN];
  n = 0;
  dp = skip(basicvars.datacur);
  while (*dp != NUL && *dp != ',') {	/* Copy value to be read */
    text[n] = *dp;
    dp++;
    n++;
  }
  text[n] = NUL;
  if (n == 0) error(ERR_BADEXPR);	/* Number string is empty */
  basicvars.datacur = dp;
  tokenize(text, readexpr, NOLINE);	/* Tokenise the expression */
  save_current();	/* Preserve our place in the program */
  basicvars.current = FIND_EXEC(&readexpr[0]);
  expression();
  restore_current();
  itemtype = GET_TOPITEM;
  switch (destination.typeinfo) {	/* Now save the value just read */
  case VAR_INTWORD:	/* Integer variable */
    switch (itemtype) {
    case STACK_INT:
      *destination.address.intaddr = pop_int();
      break;
    case STACK_FLOAT:
      *destination.address.intaddr = TOINT(pop_float());
      break;
    default:
      error(ERR_TYPENUM);
    }
    break;
  case VAR_FLOAT:	/* Floating point variable */
    switch (itemtype) {
    case STACK_INT:
      *destination.address.floataddr = TOFLOAT(pop_int());
      break;
    case STACK_FLOAT:
      *destination.address.floataddr = pop_float();
      break;
    default:
      error(ERR_TYPENUM);
    }
    break;
  case VAR_INTBYTEPTR:	/* Pointer to byte-sized integer */
    check_write(destination.address.offset, sizeof(byte));
    switch (itemtype) {
    case STACK_INT:
      basicvars.offbase[destination.address.offset] = pop_int();
      break;
    case STACK_FLOAT:
      basicvars.offbase[destination.address.offset] = TOINT(pop_float());
      break;
    default:
      error(ERR_TYPENUM);
    }
    break;
  case VAR_INTWORDPTR:	/* Pointer to word-sized integer */
    switch (itemtype) {
    case STACK_INT:
      store_integer(destination.address.offset, pop_int());
      break;
    case STACK_FLOAT:
      store_integer(destination.address.offset, TOINT(pop_float()));
      break;
    default:
      error(ERR_TYPENUM);
    }
    break;
  case VAR_FLOATPTR:	/* Pointer to floating point variable */
    switch (itemtype) {
    case STACK_INT:
      store_float(destination.address.offset, TOFLOAT(pop_int()));
      break;
    case STACK_FLOAT:
      store_float(destination.address.offset, pop_float());
      break;
    default:
      error(ERR_TYPENUM);
    }
    break;
  default:
    error(ERR_VARNUMSTR);
  }
}

/*
** 'read_string' is called when a string variable is found on a
** 'READ' statement. The data pointer is left pointing at the ','
** or NUL at the end of the line after the field
*/
static void read_string(lvalue destination) {
  int32 length;
  byte *start, *cp;
  start = cp = skip(basicvars.datacur);
  if (*cp == '\"') {	/* String is in quotes */
    start++;
    do
      cp++;
    while (*cp != NUL && *cp != '\"');
    if (*cp != '\"') error(ERR_QUOTEMISS);	/* " missing */
    length = cp-start;
    do	/* Skip '"' and find next field */
      cp++;
    while (*cp != NUL && *cp != ',');
  }
  else {
    while (*cp != NUL && *cp != ',') cp++;	/* Find end of string */
    length = cp-start;
  }
  basicvars.datacur = cp;
  switch (destination.typeinfo) {	/* Now save the value just read */
  case VAR_STRINGDOL:	/* String variable */
    if (destination.address.straddr->stringlen != length) {
      free_string(*destination.address.straddr);	/* Dispose of old string */
      destination.address.straddr->stringlen = length;
      destination.address.straddr->stringaddr = alloc_string(length);
    }
    if (length != 0) memmove(destination.address.straddr->stringaddr, start, length);
    break;
  case VAR_DOLSTRPTR:	/* Pointer to '$<string>' */
    check_write(destination.address.offset, length+1);   /* +1 for CR at end */
    if (length != 0) memmove(&basicvars.offbase[destination.address.offset], start, length);
    basicvars.offbase[destination.address.offset+length] = CR;
    break;
  default:
    error(ERR_VARNUMSTR);
  }
}

/*
** 'exec_read' deals with the Basic 'READ' statement.
*/
void exec_read(void) {
  lvalue destination;
  basicvars.current++;		/* Skip READ */
  if (ateol[*basicvars.current]) return;	/* Return if there is nothing to do */
  if (basicvars.runflags.outofdata) error(ERR_DATA);	     /* Have run out of data statements */
  while (TRUE) {
    get_lvalue(&destination);
    find_data();
    if ((destination.typeinfo & TYPEMASK)<=VAR_FLOAT)	/* Numeric value */
      read_numeric(destination);
    else {	/* Character string */
      read_string(destination);
    }
    if (*basicvars.current != ',') break;	/* Escape from loop if there is nothing left to do */
    basicvars.current++;
  }
  check_ateol();
}

/*
** 'exec_repeat' handles the start of a 'REPEAT' loop
*/
void exec_repeat(void) {
  basicvars.current++;		/* Skip REPEAT token */
  if (*basicvars.current == ':') basicvars.current++;	/* Found a ':' - Move past it */
  if (*basicvars.current == NUL) {	/* Nothing on line after REPEAT - Try next line */
    basicvars.current++;	/* Move to start of next line */
    if (basicvars.traces.lines) trace_line(get_lineno(basicvars.current));
    basicvars.current = FIND_EXEC(basicvars.current);
  }
  push_repeat();
}

/*
** 'exec_report' deals with the 'REPORT' statement which prints a copy
** of the last error message generated.
*/
void exec_report(void) {
  char *p;
  basicvars.current++;
  check_ateol();
  p = get_lasterror();
  emulate_vdustr(p, strlen(p));
  basicvars.printcount+=strlen(p);
}

/*
** 'restore_dataptr' deals with the 'RESTORE <line>' statement
*/
static void restore_dataptr(void) {
  byte *dest, *p;
  int32 line;
  basicvars.runflags.outofdata = FALSE;
  switch (*basicvars.current) {
  case TOKEN_XLINENUM:	/* RESTORE <line number> */
/*
** Note: set_linedest' returns a pointer to the first executable token on
** the line but we need a pointer to start of the line
*/
    dest = find_linestart(set_linedest(basicvars.current));
    basicvars.current = skip_token(basicvars.current);	/* Skip 'line number' token */
    check_ateol();
    break;
  case TOKEN_LINENUM:	/* RESTORE <line number> */
    dest = GET_ADDRESS(basicvars.current, byte *);
    dest = find_linestart(dest);
    basicvars.current = skip_token(basicvars.current);	/* Skip 'line number' token */
    check_ateol();
    break;
  case '+':		/* Destination is given as an offset from the next line */
    basicvars.current++;
    line = eval_integer();
    check_ateol();
    p = basicvars.current;
    while (*p != NUL) p = skip_token(p);	/* Find the start of the next line */
    p++;		/* Point at start of next line */
/*
** The line count is decrement by one as 'RESTORE +1' moves
** the data pointer to this line and we have just advanced to
** the line
*/
    line--;
    while (!AT_PROGEND(p) && line>0) {
      p+=GET_LINELEN(p);
      line--;
    }
    if (AT_PROGEND(p)) {	/* Reached end of program and no DATA statements were found */
      basicvars.runflags.outofdata = TRUE;
      return;		/* Return as there is nothing more to do */
    }
    dest = p;
    break;
  default:
    if (ateol[*basicvars.current])	/* RESTORE on its own */
      dest = basicvars.start;	/* Start at beginning of program */
    else {	/* RESTORE followed by an expression */
      line = eval_integer();		/* Find number of line */
      check_ateol();
      dest = find_line(line);
      if (get_lineno(dest) != line) error(ERR_LINEMISS, line);
    }
  }
/*
** 'dest' points at the start of the line that is the target of the
** 'RESTORE' statement. Look for a DATA statement at this point or
** after it
*/
  while (!AT_PROGEND(dest) && *FIND_EXEC(dest) != TOKEN_DATA) {
    dest+=GET_LINELEN(dest);
  }
  if (AT_PROGEND(dest))		/* No DATA statement was found */
    basicvars.runflags.outofdata = TRUE;
  else {
/*
** Point at DATA token before first item of data. The code needs to
** point here to allow the case 'DATA, ...' (where there is a comma
** immediately after the DATA token) to work. The comma would
** otherwise be skipped by the 'find data' function, that is, the
** first field would be missed.
*/
    basicvars.datacur = get_srcaddr(FIND_EXEC(dest))-1;
  }
}

/*
** 'exec_restore' handles the Basic 'RESTORE' statement.
*/
void exec_restore(void) {
  basicvars.current++;		/* Skip RESTORE token */
  switch (*basicvars.current) {
  case TOKEN_ERROR:	/* RESTORE ERROR */
    basicvars.current = skip_token(basicvars.current);
    check_ateol();
    if (GET_TOPITEM != STACK_ERROR) error(ERR_ERRNOTOP);	/* Saved error block not on top of stack */
    basicvars.error_handler = pop_error();
    break;
  case TOKEN_DATA:	/* RESTORE DATA */
    basicvars.current = skip_token(basicvars.current);
    check_ateol();
    if (GET_TOPITEM != STACK_DATA) error(ERR_DATANOTOP);	/* Saved DATA pointer not on top of stack */
    basicvars.datacur = pop_data();
 /* Note: this does not restore the 'out of data' flag */
    break;
  default:	/* Move 'DATA' pointer */
    restore_dataptr();
  }
}

/*
** 'exec_return' handles returns from GOSUB-type subroutines
*/
void exec_return(void) {
  gosubinfo returnblock;
  basicvars.current++;		/* Skip RETURN token */
  check_ateol();
  if (basicvars.gosubstack == NIL) error(ERR_RETURN);
  if (GET_TOPITEM != STACK_GOSUB) empty_stack(STACK_GOSUB);	/* Throw away unwanted entries on Basic stack */
  returnblock = pop_gosub();
  if (basicvars.traces.branches) trace_branch(basicvars.current, returnblock.retaddr);
  basicvars.current = returnblock.retaddr;
}

/*
** 'exec_run' deals with the 'RUN' command.
** This interpreter supports an extended version of 'RUN' where the
** line number from which to start program execution can be given. It
** is also possible to specift a file name after the command, so that
** it in fact works just like 'CHAIN'.
*/
void exec_run(void) {
  basicstring string;
  stackitem topitem;
  byte *bp;
  int32 line;
  char *filename;
  basicvars.current++;		/* Skip RUN token */
  bp = NIL;
  if (!ateol[*basicvars.current]) {	/* RUN <filename> or RUN <linenumber> found */
    expression();
    topitem = GET_TOPITEM;
    switch (topitem) {
    case STACK_INT: case STACK_FLOAT:
      if (topitem == STACK_INT)
        line = pop_int();
      else {
        line = TOINT(pop_float());
      }
      if (line<0 || line>MAXLINENO) error(ERR_LINENO);
      bp = find_line(line);
      if (get_lineno(bp) != line) error(ERR_LINEMISS, line);
      break;
    case STACK_STRING: case STACK_STRTEMP:
      string = pop_string();
      filename = tocstring(string.stringaddr, string.stringlen);
      if (topitem == STACK_STRTEMP) free_string(string);
      check_ateol();
      clear_error();
      clear_varlists();
      clear_strings();
      clear_heap();
      read_basic(filename);
      break;
    default:
      error(ERR_BADOPER);
    }
  }
  run_program(bp);
}

/*
** 'exec_stop' deals with the 'STOP' statement
*/
void exec_stop(void) {
  basicvars.current++;
  check_ateol();
  error(ERR_STOP);
}

/*
** 'exec_swap' deals with the 'SWAP' statement that swaps the values of
** two variables or arrays
*/
void exec_swap(void) {
  lvalue first, second;
  basicvars.current++;		/* Skip SWAP token */
  get_lvalue(&first);
  if (*basicvars.current != ',') error(ERR_COMISS);
  basicvars.current++;		/* Skip ',' token */
  get_lvalue(&second);
  check_ateol();
  if ((first.typeinfo <= VAR_FLOAT || (first.typeinfo >= VAR_INTBYTEPTR && first.typeinfo <= VAR_FLOATPTR)) &&
     (second.typeinfo <= VAR_FLOAT || (second.typeinfo >= VAR_INTBYTEPTR && second.typeinfo <= VAR_FLOATPTR))) {
/* Switching numeric values */
    int32 ival1 = 0, ival2 = 0;
    static float64 fval1, fval2;
    boolean isint = 0;
    switch (first.typeinfo) {		/* Fetch first operand */
    case VAR_INTWORD:
      ival1 = *first.address.intaddr;
      isint = TRUE;
      break;
    case VAR_FLOAT:
      fval1 = *first.address.floataddr;
      isint = FALSE;
      break;
    case VAR_INTBYTEPTR:
      check_write(first.address.offset, sizeof(byte));
      ival1 = basicvars.offbase[first.address.offset];
      isint = TRUE;
      break;
    case VAR_INTWORDPTR:
      ival1 = get_integer(first.address.offset);
      isint = TRUE;
      break;
    case VAR_FLOATPTR:
      fval1 = get_float(first.address.offset);
      isint = FALSE;
      break;
    default:
      error(ERR_BROKEN, __LINE__, "mainstate");
    }

/* Fetch the second operand and store the first in its place */

    switch (second.typeinfo) {
    case VAR_INTWORD:
      ival2 = *second.address.intaddr;
      *second.address.intaddr = isint ? ival1 : TOINT(fval1);
      isint = TRUE;	/* Now change type flag to type of second value */
      break;
    case VAR_FLOAT:
      fval2 = *second.address.floataddr;
      *second.address.floataddr = isint ? TOFLOAT(ival1) : fval1;
      isint = FALSE;
      break;
    case VAR_INTBYTEPTR:
      check_write(second.address.offset, sizeof(byte));
      ival2 = basicvars.offbase[second.address.offset];
      basicvars.offbase[second.address.offset] = isint ? ival1 : TOINT(fval1);
      isint = TRUE;
      break;
    case VAR_INTWORDPTR:
      ival2 = get_integer(second.address.offset);
      store_integer(second.address.offset, isint ? ival1 : TOINT(fval1));
      isint = TRUE;
      break;
    case VAR_FLOATPTR:
      fval2 = get_float(second.address.offset);
      store_float(second.address.offset, isint ? TOFLOAT(ival1) : fval1);
      isint = FALSE;
      break;
    default:
      error(ERR_BROKEN, __LINE__, "mainstate");
    }

/* Finally store the second operand in place of the first */

    switch (first.typeinfo) {
    case VAR_INTWORD:
      *first.address.intaddr = isint ? ival2 : TOINT(fval2);
      break;
    case VAR_FLOAT:
      *first.address.floataddr = isint ? TOFLOAT(ival2) : fval2;
      break;
    case VAR_INTBYTEPTR:
      basicvars.offbase[first.address.offset] = isint ? ival2 : TOINT(fval2);
      break;
    case VAR_INTWORDPTR:
      store_integer(first.address.offset, isint ? ival2 : TOINT(fval2));
      break;
    case VAR_FLOATPTR:
      store_float(first.address.offset, isint ? TOFLOAT(ival2) : fval2);
      break;
    default:
      error(ERR_BROKEN, __LINE__, "mainstate");
    }
  }
  else if (first.typeinfo == VAR_STRINGDOL || first.typeinfo == VAR_DOLSTRPTR) {
    basicstring stringtemp;
    if (second.typeinfo != VAR_STRINGDOL && second.typeinfo != VAR_DOLSTRPTR) error(ERR_NOSWAP);
    if (first.typeinfo == VAR_STRINGDOL && second.typeinfo == VAR_STRINGDOL) {	/* Swap aaa$ and bbb$ */
      stringtemp = *first.address.straddr;
      *first.address.straddr = *second.address.straddr;
      *second.address.straddr = stringtemp;
    }
    else if (first.typeinfo == VAR_DOLSTRPTR && second.typeinfo == VAR_DOLSTRPTR) {	/* Swap $aaa and $bbb */
      int32 len1, len2;
      len1 = get_stringlen(first.address.offset)+1;	/* +1 for CR at end of string */
      len2 = get_stringlen(second.address.offset)+1;
      check_write(first.address.offset, len2);
      check_write(second.address.offset, len1);
      memmove(basicvars.stringwork, &basicvars.offbase[first.address.offset], len1);
      memmove(&basicvars.offbase[first.address.offset], &basicvars.offbase[second.address.offset], len2);
      memmove(&basicvars.offbase[second.address.offset], basicvars.stringwork, len1);
    }
    else {	/* Swap aaa$ and $bbb or $aaa and bbb$ */
      int len;
      if (first.typeinfo == VAR_DOLSTRPTR) {	/* Turn it into aaa$ and $bbb */
        lvalue temp = first;
        first = second;
        second = temp;
      }
      check_write(second.address.offset, first.address.straddr->stringlen+1);
/* Move '$bbb' string to a  proper string */
      stringtemp.stringlen = len = get_stringlen(second.address.offset);
      stringtemp.stringaddr = alloc_string(len);
      if (len>0) memmove(stringtemp.stringaddr, &basicvars.offbase[second.address.offset], len);
/* Copy 'aaa$' string to address of other string and turn it into a '$xxx' type string */
      len = first.address.straddr->stringlen;	/* Get length of first string */
      if (len>0) memmove(&basicvars.offbase[second.address.offset], first.address.straddr->stringaddr, len);
      basicvars.offbase[second.address.offset+len] = CR;
      free_string(*first.address.straddr);
      *first.address.straddr = stringtemp;
    }
  }
  else if ((first.typeinfo & VAR_ARRAY) != 0) {
    basicarray *arraytemp;
    if (second.typeinfo != first.typeinfo) error(ERR_NOSWAP);
    arraytemp = *first.address.arrayaddr;
    *first.address.arrayaddr = *second.address.arrayaddr;
    *second.address.arrayaddr = arraytemp;
  }
  else {	/* Cannot swap these operands */
    error(ERR_NOSWAP);
  }
}

/*
** 'exec_sys' handles the Basic 'SYS' statement, which is used
** to make operating system calls. These are often refered to
** as 'SWIs'.
*/
void exec_sys(void) {
  int32 n, parmcount, flags, swino = 0;
  int32 inregs[MAXSYSPARMS], outregs[MAXSYSPARMS];
  stackitem parmtype;
  basicstring descriptor, tempdesc[MAXSYSPARMS];
  lvalue destination;
  basicvars.current++;
  expression();		/* Fetch the SWI name or number */
  parmtype = GET_TOPITEM;
  switch (parmtype) {	/* Untangle the SWI number */
  case STACK_INT:
    swino = pop_int();
    break;
  case STACK_FLOAT:
    swino = TOINT(pop_float());
    break;
  case STACK_STRING: case STACK_STRTEMP:
    descriptor = pop_string();
    swino = emulate_getswino(descriptor.stringaddr, descriptor.stringlen);
    if (parmtype == STACK_STRTEMP) free_string(descriptor);
    break;
  default:
    error(ERR_TYPENUM);
  }
/* Set up default values for all possible parameters */
  for (n=0; n<MAXSYSPARMS; n++) {
    inregs[n] = 0;
    tempdesc[n].stringaddr = NIL;
  }
  parmcount = 0;
  if (*basicvars.current == ',') basicvars.current++;
/* Now gather the parameters for the SWI call */
  while (!ateol[*basicvars.current] && *basicvars.current != TOKEN_TO) {
    if (*basicvars.current != ',') {	/* Parameter position is not empty */
      expression();
      parmtype = GET_TOPITEM;
      switch (parmtype) {
      case STACK_INT:
        inregs[parmcount] = pop_int();
        break;
      case STACK_FLOAT:
        inregs[parmcount] = TOINT(pop_float());
        break;
      case STACK_STRING: case STACK_STRTEMP: {
        int32 length;
        char *cp;
        descriptor = pop_string();
/* Copy the string to a temporary location and append a NULL */
        length = descriptor.stringlen;
        tempdesc[parmcount].stringlen = length+1;
        tempdesc[parmcount].stringaddr = cp = alloc_string(length+1);
        if (length>0) memmove(cp, descriptor.stringaddr, length);
        cp[length] = NUL;
        if (parmtype == STACK_STRTEMP) free_string(descriptor);
        inregs[parmcount] = CAST(cp, byte *)-basicvars.offbase;
        break;
      }
      default:
        error(ERR_VARNUMSTR);	/* Parameter must be an integer or string value */
      }
    }
    parmcount+=1;
    if (parmcount>=MAXSYSPARMS) error(ERR_SYSCOUNT);
    if (*basicvars.current == ',')
      basicvars.current++;	/* Point at start of next parameter */
    else if (!ateol[*basicvars.current] && *basicvars.current != TOKEN_TO) {
      error(ERR_SYNTAX);
    }
  }
/* Make the SWI call */
  emulate_sys(swino, inregs, outregs, &flags);
  for (n=0; n<MAXSYSPARMS; n++) {	/* Discard any temporary strings used */
    if (tempdesc[n].stringaddr != NIL) free_string(tempdesc[n]);
  }
  if (ateol[*basicvars.current]) return;	/* Not returning any parameters so just go home */
  basicvars.current++;
  parmcount = 0;
/* Copy SWI values returned to the return parameters */
  while (!ateol[*basicvars.current] && *basicvars.current != ';') {
    if (*basicvars.current != ',') {	/* Want this return value */
      get_lvalue(&destination);
      store_value(destination, outregs[parmcount], STRINGOK);
    }
    parmcount++;
    if (parmcount>=MAXSYSPARMS) error(ERR_SYSCOUNT);
    if (*basicvars.current == ',')	/* There is another parameter to follow - Move to its start */
      basicvars.current++;
    else if (!ateol[*basicvars.current] && *basicvars.current != ';') {
      error(ERR_SYNTAX);
    }
  }
  if (*basicvars.current == ';') {	/* Want flags as well */
    basicvars.current++;	/* Skip ';' token */
    get_lvalue(&destination);
    store_value(destination, flags, NOSTRING);
  }
  check_ateol();
}

/*
** 'exec_trace' handles the various flavours of trace command
*/
void exec_trace(void) {
  boolean yes;
  byte option;
  basicvars.current++;			/* Skip TRACE token */
  if (*basicvars.current == TOKEN_ON) {		/* Line number trace */
    basicvars.traces.enabled = TRUE;
    basicvars.traces.lines = TRUE;
  }
  else if (*basicvars.current == TOKEN_OFF) {	/* Turn off any active traces */
    basicvars.traces.enabled = FALSE;
    basicvars.traces.lines = FALSE;
    basicvars.traces.procs = FALSE;
    basicvars.traces.pause = FALSE;
    basicvars.traces.branches = FALSE;
  }
  else if (*basicvars.current == TOKEN_TO) {	/* Got 'TRACE TO <file>' */
    stackitem stringtype;
    basicstring descriptor;
    basicvars.current++;
    expression();
    check_ateol();
    stringtype = GET_TOPITEM;
    if (stringtype != STACK_STRING && stringtype != STACK_STRTEMP) error(ERR_TYPESTR);
    descriptor = pop_string();
    basicvars.tracehandle = fileio_openout(descriptor.stringaddr, descriptor.stringlen);
    if (stringtype == STACK_STRTEMP) free_string(descriptor);
    return;	/* As this code calls 'check_ateol' */
  }
  else if (*basicvars.current == TOKEN_CLOSE) {
    if (basicvars.tracehandle != 0) {
      fileio_close(basicvars.tracehandle);
      basicvars.tracehandle = 0;
    }
  }
  else if (ateol[*basicvars.current])		/* Got 'TRACE' on its own */
    error(ERR_BADTRACE);
  else {	/* TRACE <something> [ON|OFF] */
    option = *(basicvars.current+1);
    if (!ateol[option] && option != TOKEN_ON && option != TOKEN_OFF) error(ERR_BADTRACE);
    yes = option != TOKEN_OFF;
    switch (*basicvars.current) {
    case TOKEN_PROC: case TOKEN_FN:	/* PROC call/return trace */
      basicvars.traces.procs = yes;
      break;
    case TOKEN_GOTO:	/* Branch trace */
      basicvars.traces.branches = yes;
      break;
    case TOKEN_STEP:	/* Execute one statement at a time */
      basicvars.traces.pause = yes;
      break;
    case TOKEN_RETURN:	/* Stack backtrace */
      basicvars.traces.backtrace = yes;
      break;
    default:
      error(ERR_BADTRACE);
    }
    basicvars.traces.enabled = basicvars.traces.procs || basicvars.traces.branches;
    if (!ateol[option]) basicvars.current++;
  }
  basicvars.current++;		/* Skip TRACE option token */
  check_ateol();
}

/*
** 'exec_until' deals with the business end of a 'REPEAT' loop
*/
void exec_until(void) {
  byte *here;
  stack_repeat *rp;
  int32 result = 0;
  if (GET_TOPITEM == STACK_REPEAT)	/* REPEAT control block is top of stack */
    rp = basicvars.stacktop.repeatsp;
  else {	/* Discard stack entries as far as REPEAT control block */
    rp = get_repeat();
  }
  if (rp == NIL) error(ERR_NOTREPEAT);	/* Not in a REPEAT loop */
  if (basicvars.escape) error(ERR_ESCAPE);
  here = basicvars.current;	/* Note position of UNTIL for trace purposes */
  basicvars.current++;
  expression();
  if (GET_TOPITEM == STACK_INT)
    result = pop_int();
  else if (GET_TOPITEM == STACK_FLOAT)
    result = TOINT(pop_float());
  else {
    error(ERR_TYPENUM);
  }
  if (result == BASFALSE) {	/* Condition still false - Continue with loop */
    if (basicvars.traces.branches) trace_branch(here, rp->repeataddr);
    basicvars.current = rp->repeataddr;
  }
  else {	/* Escape from loop - Remove REPEAT control block from stack */
    pop_repeat();
    if (!ateol[*basicvars.current]) error(ERR_SYNTAX);
  }
}

/*
** 'exec_wait' deals with the basic statement 'WAIT'
*/
void exec_wait(void) {
  basicvars.current++;
  if (ateol[*basicvars.current])	/* Normal 'WAIT' statement */
    emulate_wait();
  else {	/* WAIT <time to wait> */
    int32 delay = eval_integer();
    check_ateol();
    emulate_waitdelay(delay);
  }
}

/*
** 'exec_xwhen' deals with the first reference to a 'WHEN' or an
** 'OTHERWISE' statement. In the context of the interpreter they are
** used to mark the end of the statement sequence of the preceding 'WHEN'
** clause. The function fills in the offset from the WHEN to the code
** following the CASE statement's ENDCASE.
*/
void exec_xwhen(void) {
  byte *lp, *lp2;
  int32 depth;
  lp = basicvars.current+1+OFFSIZE;	/* Skip token and offset */
  while (*lp != NUL) lp = skip_token(lp);
  lp++;		/* Point at the start of the line after the 'WHEN' or 'OTHERWISE' */
  depth = 1;
  do {
    if (AT_PROGEND(lp)) error(ERR_ENDCASE);	/* No ENDCASE found for this CASE */
    lp2 = FIND_EXEC(lp);
    if (*lp2 == TOKEN_ENDCASE) {	/* Have reached the end of a CASE statement */
      depth--;
      if (depth == 0) break;
    }
    else {	/* Check for a nested CASE statement */
      while (*lp2 != NUL && *lp2 != TOKEN_XCASE && *lp2 != TOKEN_CASE) lp2 = skip_token(lp2);
      if (*lp2 != NUL) depth++;	/* Have found one of the CASE tokens - Got a nested 'CASE' */
    }
    lp+=GET_LINELEN(lp);
  } while (TRUE);
  lp2++;	/* Skip 'ENDCASE' token */
  if (*lp2 == ':') lp2++;
  if (*lp2 == NUL) {	/* 'ENDCASE' is at end of line */
    lp2++;	/* Move to start of next line */
    lp2 = FIND_EXEC(lp2);
  }
  set_dest(basicvars.current+1, lp2);
  exec_elsewhen();	/* Now go and branch to the ENDCASE */
}

/*
** 'exec_while' is called when a 'WHILE' statement is found. It checks
** that the statement is valid and evaluates it for the first time.
** A 'while' data structure is created on the stack and the loop entered.
** Most of the work is done by the 'ENDWHILE': this evaluates the
** expression again and either branches back to the start of the loop
** if it is still 'TRUE' or drops through to the next statement.
** Note: if the WHILE loop is to be skipped because the expression
** evaluates to 'FALSE' the first time it is seen, the code will look
** for the first ENDWHILE at the appropriate depth of nesting and call
** that the terminating ENDWHILE for the loop. In most cases this will
** be fine, but it is possible to write legitimate code such as
** 'IF A% THEN ENDWHILE' where this function will pick the ENDWHILE
** here as the one it wants. Obviously this could lead to unexpected
** results. The behaviour of the code in fact matches the Acorn Basic
** interpreter in this respect.
**
** The offset to the first statement of the loop could be stored after
** the WHILE token. The code will then look like a IF statement with
** two embedded pointers
*/
void exec_while(void) {
  byte *expr, *here;
  int32 result = 0;
  here = basicvars.current;	/* Keep a pointer to the 'WHILE' token */
  basicvars.current+=OFFSIZE+1;	/* Skip 'WHILE' and 'ENDWHILE' branch offset */
  expr = basicvars.current;
  expression();
  if (GET_TOPITEM == STACK_INT)
    result = pop_int();
  else if (GET_TOPITEM == STACK_FLOAT)
    result= TOINT(pop_float());
  else {
    error(ERR_TYPENUM);
  }
  if (result != BASFALSE) {	/* If result is not false, enter the loop */
    if (*basicvars.current == ':') basicvars.current++;	/* Loop body found on same line as WHILE statement */
    if (*basicvars.current == NUL) {	/* Loop body starts on next line */
      basicvars.current++;
      if (basicvars.traces.lines) trace_line(get_lineno(basicvars.current));
      basicvars.current = FIND_EXEC(basicvars.current);	/* Move to first token on next line */
    }
    push_while(expr);
  }
  else {	/* Initial 'WHILE' expression value is 'FALSE', so skip loop altogether */
    if (*here == TOKEN_WHILE) {	/* Branch destination has been filled in */
      here++;
      basicvars.current = GET_DEST(here);
      if (basicvars.traces.branches) trace_branch(here, basicvars.current);
    }
    else {	/* Have to look for the 'ENDWHILE'. 'basicvars.current' points at token after expression here */
      int32 depth = 1;
      while (depth>0) {
        if (*basicvars.current == NUL) {	/* At the end of a line */
          basicvars.current++;
          if (AT_PROGEND(basicvars.current)) error(ERR_ENDWHILE);	/* No 'ENDWHILE' found */
          basicvars.current = FIND_EXEC(basicvars.current);
        }
        if (*basicvars.current == TOKEN_ENDWHILE)
          depth--;
        else if (*basicvars.current == TOKEN_WHILE || *basicvars.current == TOKEN_XWHILE) {	/* Found a nested loop */
          depth++;
        }
        if (depth>0) basicvars.current=skip_token(basicvars.current);
      }
      basicvars.current++;	/* Skip the ENDWHILE token */
      if (*basicvars.current == ':') basicvars.current++;	/* Skip a ':' after the ENDWHILE */
      if (*basicvars.current == NUL) {	/* There is nothing else on the line - Skip to next line */
        basicvars.current++;
	if (basicvars.traces.lines) trace_line(get_lineno(basicvars.current));
        basicvars.current = FIND_EXEC(basicvars.current);
      }
      set_dest(here+1, basicvars.current);	/* Save the address for latet */
      *here = TOKEN_WHILE;
      if (basicvars.traces.branches) trace_branch(here, basicvars.current);
    }
  }
}

