Parameters and local variables may not be used in a look-ahead production!

Messages > Parameters and local variables may not be used in a look-ahead production!

This error message appears, if parsing with a production is controlled by a semantic code which accesses a variable declared locally or a parameter, but the production is used for a look-ahead at the same time directly or indirectly. This isn't permitted because, to avoid side effects like a doubled output, in look-ahead productions all semantic code is ignored, as far as it doesn't immediately belong to the condition of an IF or WHILE structure.

Example:

IF( Prod() )

 ...

The production Prod is used in an IF structure as a look-ahead production. Prod contains a WHILE structure, iwhich depends on the locally declared variable b.

Prod ::=

{{

bool b = true;

}}

WHILE ( b )

... {{b = false;}}  

END  

The use of class variables is tolerated in such cases, however, it can hurt const conditions in the generated code.

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