CODEWITHSUNDEEP
cparsingbisonyacclalr
user2116243
user2116243

Reputation: 303

Trying to Resolve Shift Reduce Conflicts by Changing Grammar

Given the following specification for a grammar: 

Statement → { Statement* }
      → VarDecl
      → if ( Exp ) Statement else Statement
      → while ( Exp ) Statement
      → System.out.println ( Exp ) ;
      → id = Exp ;
      → id [ Exp ]= Exp ;

These are the rules I've come up with to use in a YACC/BISON program. I have Shift/Reduce Conflicts though. 

StatementList:
    '{' StatementList Statement '}'
     |  Statement
     ;

Statement: 
    |   VarDecl
    |   IF '('Exp')' StatementList ELSE StatementList
    |   WHILE'('Exp')' StatementList
    |   SOP'('Exp')' ';'
    |   ID '=' Exp ';'
    |   ID'['Exp']' '=' Exp';'
    ;

Also tried this grammar: 

CompoundStatement:
        '{' StatementList '}'

StatementList:
    StatementList Statement
    |   Statement
    ;

Statement: 
    |   VarDecl
    |   IF '('Exp')' Statement ELSE Statement
    |   WHILE'('Exp')' Statement
    |   SOP'('Exp')' ';'
    |   ID '=' Exp ';'
    |   ID'['Exp']' '=' Exp';'
    |   CompoundStatement
    ;

Did not work either. Still had conflicts. (Though this passed the testcases I'd set up)

And neither did this:

StatementList
     : %empty /* Explicit empty production, bison 3.0+ */
     | StatementList Statement

Statement
     : '{' StatementList '}'
     | IF '('Exp')' Statement ELSE Statement
     | /* ... and the rest of the statements */

Any help?

Upvotes: 0

Views: 89

Answers (1)

rici
rici

Reputation: 241671

  1. You have an empty production for Statement. You probably didn't intend to; you certainly don't need to; and it is probably the cause of your conflicts.

  2. Your production for blocks is wrong. You need to define StatementList in order to implement Statement*, and then follow through with your original grammar:

    StatementList
     : %empty /* Explicit empty production, bison 3.0+ */
     | StatementList Statement

Statement
     : '{' StatementList '}'
     | IF '('Exp')' Statement ELSE Statement
     | /* ... and the rest of the statements */

Upvotes: 3

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