tt(DEFINEMACRO) is used to define new macros. This function expects
three arguments: 
    itemization(
    it() An identifier, being the name of the macro to define. This identifier
may only consist of uppercase or lowercase characters. Note that it can
em(not) contain numbers, nor underscore characters.
 
    it() A number, stating the number of arguments that the macro will require
once it's used. The number must be in the range 0 to 61.
    
    it() The text that the macro expands to, once used. This text may
contain the strings tt(ARG)em(x), em(x) being 1, 2, etc.. At these places the
arguments to the macro are pasted in. The numbers that identify the
arguments are 1 to 9, then A to Z and finally a to z. This gives a range of 61
expandable arguments, which is enough for all real-life applications.
    )
    For example, the following fragment defines a macro tt(bookref), which can
be used to typeset a reference to a book. It requires three arguments; say, an
author, a title and the name of a publisher:
        verb(
    DEFINEMACRO(bookref)(3)(
        Author(s):           ARG1
        Book title:          ARG2
        Published by:        ARG3
    )
        )
    Such a macro could be used as follows:
        verb(
    bookref(Sobotta/Becher)
           (Atlas der Anatomie des Menschen)
           (Urban und Schwarzenberg, Berlin, 1972)
        )
    When called, it would produce the following output:
        verb(
        Author(s):           Sobotta/Becher
        Book title:          Atlas der Anatomie des Menschen
        Published by:        Urban und Schwarzenberg, Berlin, 1972
        )
    While applying a macro, the values of the three arguments are pasted to
the places where tt(ARG1), tt(ARG2) etc. occur in the definition.

Note the following when defining new macros:
    itemization(
    it() The argument containing the name of the new macro, tt((bookref)) in
the above example, must occur right after tt(DEFINEMACRO). No spaces are
allowed in between. Space characters and newlines may however occur following
this first argument.
    
    This behavior of the tt(yodl) program is similar to the usage of the
defined macro: the author information must, enclosed in parentheses, follow
right after the tt(bookref) identifier. I implemented this feature to improve
the distinguishing between macros and real text. E.g., a macro tt(me) might be
defined, but the text
        verb(
    I like me (but so do you)
        )
    still is simple text; the macro tt(me) only is activated when a
parenthesis immediately follows it.
    
    it() Be careful when placing newlines or spaces in the definition of a new
macro. E.g., the definition, as given:
        verb(
    DEFINEMACRO(bookref)(3)(
        Author(s):           ARG1
        Book title:          ARG2
        Published by:        ARG3
    )
        )
    introduces extra newlines at the beginning and ending of the macro, which
are copied to the output each time the macro is used. The extra newline
occurs, of course, right before the sequence tt(Author(s):) and following the
evaluation of tt(ARG3). A simple backslash character at the end of the
tt(DEFINEMACRO) line would prevent the insertion of extra newline
characters:
        verb(
    DEFINEMACRO(bookref)(3)(\ 
        Author(s):           ARG1
        Book title:          ARG2
        Published by:        ARG3
    )
        )
    
    it() Note that when a macro is used which requires no arguments at all,
one empty argument still must be specified. E.g., my macro package (see
chapter ref(MACROPACKAGE)) defines a macro tt(it) that starts a bullet item in
a list. The macro takes no arguments, but still must be typed as tt(it()).
    
    This behavior is consistent: it helps distinguish which identifiers are
macros and which are simple text.

    it() Macro arguments may evaluate to text. When a \ is appended to the
macro-argument, or in the default input handling within a non-zero white-space
level (see section ref(INCWSLEVEL)) this may invalidate a subsequent macro
call. E.g., the macro
        verb(
    DEFINEMACRO(oops)(1)(
        ARG1
        XXnl()
    )
        )
    when called as tt(oops(hello world)), produces the output:
        verb(
    hello worldXXnl()
        )
    To prevent this gluing to arguments to subsequent macros, a single tt(+)
should be prepended to the macro call:
        verb(
    DEFINEMACRO(oops)(1)(
        ARG1
        +XXnl()
    )
        )
    See also section ref(PLUSIDENT) obout the `+identifier'-sequence.

    it() Note the preferred layout of macro definitions and macro
calls. Adhere to this form, to prevent drowning in too many parentheses. In
particular:
        itemization(
        it() Put all elements of the macro definition on one line, except for
the macro-expansion itself. Each expansion element should be on a line by
itself.
        it() When calling macros put the macro's arguments underneath each
other. If the macrolists themselves contain macro-calls, put each call again
on a line of its own, indenting one tab-position beyond the location of the
opening parenthesis of the argument.
        it() No continnuation backslashes are required between arguments.
        it() With complex calls, indent just the arguments, and put the
parentheses in their required of logical locations.
        )
    Example of a complex call:
        verb(
        complex(
            first(
                ARG1
            )(
                ARG2
                +XXnl()
            )
            ARG3
            +nop()
            ARG4
            +XXnl()
        )
            )
    it() Macro expansion proceeds as follows:
        itemization(
        it() The arguments are read from the input
        it() The contents of the arguments then replace their tt(ARGx)
references in the macro's definition (in some exceptional cases, clearly
indicated as such when applicable, the arguments themselves are evaluated
first, and then these evaluated arguments are used as replacements for their
corresponding tt(ARGx) references).
        it() The now modified macro is read by Yodl's lexical scanner. This
may result in yet another macro expansion, which will then be evaluated
recursively. 
        it() Eventually, all expansion is completed (well, should complete,
since Yodl doesn't test for eternal recursion) and scanning of the input
continues beyond the original macro call.
        )
    For example, assume we have the following two macros:
        verb(
    DEFINEMACRO(First)(1)( 
        Hello ARG1 
        +XXnl() 
    )
    DEFINEMACRO(Second)(1)( 
        First(ARG1) 
        First(ARG1) 
    )
        )
    and the following call is issued:
        verb(
    Second(Yodl)
        )
    then the following happens:
        itemization(
        it() tt(Second(Yodl)) is read as encountered.
        it() tt(ARG1) in tt(Second) is replaced by YODL, and the resulting
macro body is sent to the lexical scanner for evaluation: It will see:
        verb(
    First(Yodl)First(Yodl)
        )
        it() The first call to tt(First()) is now evaluated. This puts
(after replacing tt(ARG1) by YODL) the following on the scanner's input:
        verb(
    Hello Yodl+XXnl()First(Yodl)
        )
        it() tt(Hello Yodl) contains no macro call, so it is written to the
output stream. Remains:
        verb(
    +XXnl()First(Yodl)
        )
        it() Assume tt(XXnl()) merely contains a newline (represented by
tt(\n), here), so tt(+XXnl()) is now replaced by tt(\n). This results in the
following input for the lexical scanner: 
        verb(
    \nFirst(Yodl)
        )
        it() The tt(\n) is now written to the output stream, and the scanner
sees: 
        verb(
    First(Yodl)
        )
        it() The second call to tt(First()) is now evaluated. This puts
the following on the scanner's input:
        verb(
    Hello Yodl+XXnl()
        )
        it() tt(Hello Yodl) is written to the output stream. Remains:
        verb(
    +XXnl()
        )
        it() tt(+XXnl()) is now replaced by tt(\n). The lexical scanner sees:
        verb(
    \n
        )
        it() The newline is printed and we're done.
        )
    )





    



