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$DEFINE: Deferred macro definition

$DEFINE behaves like the FWEB macro command @m, but it is intended to appear in the code part, not the definition part (so it is processed during output, not input). Thus, the code fragment

a = A;
$DEFINE(A 1)@%
a = A;

tangles to

a= A;
a= 1;

(Notice how the @% command was used to kill an unwanted newline, analogous to the dnl macro in m4.)

In the above example, one could also say $DEFINE(A=1). To define a macro with arguments, say something like $DEFINE(A(x)x*x). Do not say $DEFINE(A(x)=x*x), as in this case the equals sign will be included in the macro expansion. One must use the equals sign as a means of preventing parentheses from being interpreted as an argument in examples like

$DEFINE(A=(x))

This expands to (x).

A completely equivalent shorthand notation for $DEFINE is $M.