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Pseudo (invisible) operators

Pseudo- or invisible operators are ignored by FTANGLE and not printed by FWEAVE; however, they retain grammatical significance that helps out FWEAVE in its attempts to understand the syntax.

@e: Pseudo-expression

@e is an invisible expression (`pseudo-expression') (see Pseudo-operators). It is sometimes useful in situations where FWEAVE's pretty-printing has broken down because it didn't properly understand the language syntax. If, for example, FWEAVE failed to properly parse the C statement

     p = (int (*))q;
     

one might get things to work properly by saying

     p = (int (*@e))q;
     

In this particular case, one is patching up a deficiency (all right, a bug) in FWEAVE's "production rules." (This particular bug may no longer exist.) However, there are other situations in which the use of @e might be necessary. Consider, for example, the C macro definition

     #define A(x) = x
     

Here the replacement text of the macro is = x, which by itself is not a valid construction in C. When the -1 or -2 options are used, FWEAVE will report an "irreducible scrap sequence" in this situation (although it may typeset it correctly anyway). To eliminate the warning message, say instead

     #define A(x) @e = x
     

Now the fragment @e = x is interpreted as a valid expression.