problem with Bison

Hello group,


I have a problem with the following Bison grammar.


----------------begin test.y----------------
%{
#include <stdio.h>


int yylex()
{
    return getchar();
}


void yyerror(char *msg)
{
    printf("%s\n", msg);
}
%}


%%


phrase:
    assignment '\n'
| expression '\n'
;


assignment:
  '#' paramlist '=' expression
;


paramlist:
/*empty*/
| '#' paramlist
;


expression:
  '#'
| application
;


application: expression expression
;


%%


int main()
{
    yyparse();


    return 0;
}
----------------end test.y----------------


This is supposed to handle both "expressions", which have the
form "#\n", "##\n", "###\n", etc., and "definitions", which have
the form "#=##\n", "##=###\n", etc..


However, the resulting program gives a parse error on "##\n", i.e.
basically on any expression except for "#\n".


I suppose the problem is that Bison can't tell by looking at the
start of the input whether it is an expression or a definition.
The only solution I see is to have definitions start with some
other symbol, say'!', but I think that's ugly, so I'd rather avoid that.


Has anyone an idea to get Bison to do what I want?


Thanks in advance,


Stephan Houben
[Well, the two shift-reduce conflicts that yacc gets should give you a
starting place. The easiest fix is to flatten the grammar, that is, get
rid of the assignment rule:


phrase:
  '#' paramlist '=' expression '\n'
| expression '\n' ;


You also need to fix your application rule which is extremely ambiguous,
e.g:


application: '#' expression ;


-John]

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