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I am writing a c-like language, but for grammar shown below:

module: module declORFunc
    | declORFunc
    ;

declORFunc: decl
    | func

decl: CONST_opt btype varDef_list SEMICOLON ;

CONST_opt: /* empty */ | CONST ;

btype: INT | FLOAT ;

...

func: functype ID LPAREN funcFParams_opt RPAREN blockStmt ;

functype: INT | FLOAT | VOID ;

Because yacc is LALR(1), when processing token INT, it exhibits a shift-reduce conflict during grammar resolution for both sytanx start with INT ID. For more detail:

Sy.y: warning: shift/reduce conflict on token INT [-Wcounterexamples]
  First example: • INT ID LPAREN funcFParams_opt RPAREN blockStmt $end
  Shift derivation
    $accept
    ↳ 0: module                                                                 $end
         ↳ 2: declORFunc
              ↳ 4: func
                   ↳ 20: functype    ID LPAREN funcFParams_opt RPAREN blockStmt
                         ↳ 21: • INT
  Second example: • INT varDef_list SEMICOLON $end
  Reduce derivation
    $accept
    ↳ 0: module                                                  $end
         ↳ 2: declORFunc
              ↳ 3: decl
                   ↳ 5: CONST_opt btype    varDef_list SEMICOLON
                        ↳ 6: ε •  ↳ 8: INT

I trid:

  • replace btype and functype with type: INT | FLOAT | VOID;
  • add %proc to force yacc to shift into decl before reduce into func.

How can I resolve this conflict?

Improve this question
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  • I don't think you can; C is not LALR(1), so no LALR(1) parser is going to be able to fully parse it. You can eliminate one of your shift/reduce errors by changing to "functype: btype | VOID;" but I don't think you can eliminate the ID problem. (You can make the bison grammar accept illegal C and test for the illegal bits in code and yyerror() out manually if you really want to use bison to parse your C-like programs) Commented Oct 6 at 0:04
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