This is CORBA::IDLtree, a module that builds abstract syntax trees
from CORBA IDL.

The main export is sub Parse_File which takes an IDL input file name
as the parameter, and returns a reference to an array of references
to the root nodes constructed (or 0 if there were syntax errors.)

Parse_File uses two auxiliary data structures:
  @include_path  - Paths where to look for included IDL files
  %defines       - Symbol definitions for the preprocessor
                   (cf. the -D switch on many C compilers)
                   where -DSYM=VAL is represented as
                   $defines{SYM} = VAL. -DSYM is represented as
                   $defines{SYM} = 1.

A further export is the sub Dump_Symbols which takes the return value
of Parse_File as the parameter, and prints the trees constructed to
stdout in IDL syntax.

-----------------------------------------------------------------------------

SYMBOL TREE STRUCTURE

The following description of the structure of the symbol tree
applies to CORBA::IDLtree version >= 1.0.  The structure
has been changed w.r.t. previous releases, for example the
INTERFACE node now has an "abstract" flag. Also, all the
scalars used as constants, e.g. $INTERFACE, have been changed to
subroutines, e.g. &INTERFACE, to better express the constness
of these values. However, it is intended to keep further
changes to the user interface to a minimum, i.e. the IDLtree
programming interface is now considered stable.


A "thing" in the symbol tree can be either a reference to a node, or a
reference to an array of references to nodes.

A node is a four-element array with the elements
  [0] => TYPE (MODULE|INTERFACE|STRUCT|UNION|ENUM|TYPEDEF...)
  [1] => NAME
  [2] => SUBORDINATES
  [3] => SCOPEREF

Some IDL types are representable as a simple numeric constant;
they do not require nodes.  We'll call these types "elementary".
Elementary types are the scalar types, e.g. boolean, short,
unsigned long long, any, string.

Other IDL types cannot be represented in this way, they require
more information. An enum, for example, requires the enumeration
literals. These types are represented as nodes. The TYPE element
contains a numeric ID identifying what IDL type the node represents.

The NAME element, unless specified otherwise, simply holds the name string
of the respective IDL syntactic item.

The SUBORDINATES element depends on the node type.
Sometimes an item in the SUBORDINATES may contain either a type ID or
a reference to the defining node; we will call that a `type descriptor'.
Which of the two alternatives is in effect can be determined via the
isnode() function.

Contents of SUBORDINATES:

  MODULE or       Reference to an array of nodes (symbols) which are defined
  INTERFACE       within the module or interface. In the case of INTERFACE,
                  element [0] in this array will contain a reference to a
                  further array which in turn contains references to the
                  parent interface(s) if inheritance is used, or the null
                  value if the current interface is not derived by
                  inheritance. Element [1] is the "abstract" flag which is
                  non-zero for interfaces declared abstract.

  INTERFACE_FWD   Reference to the node of the full interface declaration.

  STRUCT or       Reference to an array of node references representing the
  EXCEPTION       member components of the struct or exception.   
                  Each member representative node is a triplet consisting
                  of (TYPE, NAME, <dimref>).
                  The <dimref> is a reference to a list of dimension numbers,
                  or is 0 if no dimensions were given.

  UNION           Similar to STRUCT/EXCEPTION, reference to an array of
                  nodes. For union members, the member node has the same
                  structure as for STRUCT/EXCEPTION.
                  However, the first node contains a type descriptor for
                  the discriminant type.
                  The TYPE of a member node may also be CASE or DEFAULT.
                  For CASE, the NAME is unused, and the SUBORDINATE contains
                  a reference to a list of the case values for the following
                  member node.
                  For DEFAULT, both the NAME and the SUBORDINATE are unused.

  ENUM            Reference to the array of enum value literals.

  TYPEDEF         Reference to a two-element array: element 0 contains a
                  reference to the type descriptor of the original type;
                  element 1 contains a reference to an array of dimension
                  numbers, or the null value if no dimensions are given.

  SEQUENCE        As a special case, the NAME element of a SEQUENCE node
                  does not contain a name (as sequences are anonymous 
                  types), but instead is used to hold the bound number.
                  If the bound number is 0, then it is an unbounded
                  sequence. The SUBORDINATES element contains the type
                  descriptor of the base type of the sequence. This 
                  descriptor could itself be a reference to a SEQUENCE
                  defining node (that is, a nested sequence definition.)
                  Bounded strings are treated as a special case of sequence.
                  They are represented as references to a node that has
                  BOUNDED_STRING or BOUNDED_WSTRING as the type ID, the bound
                  number in the NAME, and the SUBORDINATES element is unused.

  CONST           Reference to a two-element array. Element 0 is a type
                  descriptor of the const's type; element 1 is a reference
                  to an array containing the RHS expression symbols.

  FIXED           Reference to a two-element array. Element 0 contains the
                  digit number and element 1 contains the scale factor.
                  The NAME component in a FIXED node is unused.

  VALUETYPE       [0] => $is_abstract (boolean)
                  [1] => reference to a tuple (two-element list) containing
                         inheritance related information:
                         [0] => $is_truncatable (boolean)
                         [1] => \@ancestors (reference to array containing
                                references to ancestor nodes)
                  [2] => \@members: reference to array containing references
                         to tuples (two-element lists) of the form:
                         [0] => 0|PRIVATE|PUBLIC
                                A zero for this value means the element [1]
                                contains a reference to a METHOD or ATTRIBUTE.
                                In case of METHOD, the first element in the
                                method node subordinates (i.e., the return
                                type) may be FACTORY.
                         [1] => reference to the defining node.

  VALUETYPE_BOX   Reference to the defining type node.

  VALUETYPE_FWD   Subordinates unused.
                  
  ATTRIBUTE       Reference to a two-element array; element 0 is the read-
                  only flag (0 for read/write attributes), element 1 is a
                  type descriptor of the attribute's type.

  METHOD          Reference to a variable length array; element 0 is a type
                  descriptor for the return type. Elements 1 and following
                  are references to parameter descriptor nodes with the
                  following structure:
                      [0] => parameter type descriptor
                      [1] => parameter name
                      [2] => parameter mode (IN, OUT, or INOUT)
                  The last element in the variable-length array is a
                  reference to the "raises" list. This list contains
                  references to the declaration nodes of exceptions raised,
                  or is empty if there is no "raises" clause.

  INCFILE         Reference to an array of nodes (symbols) which are defined
                  within the include file. The Name element of this node
                  contains the include file name.

The SCOPEREF element is a reference back to the node of the module or 
interface enclosing the current node. If the current node is already
at the global scope level, then the SCOPEREF is 0. All nodes have this
element except for the parameter nodes of methods and the component nodes
of structs/unions/exceptions.

-- 2002/06/24  okellogg@users.sourceforge.net

