consider following grammar for C-minus;
This is a "Dangling else" problem that leads to Shift/Reduce conflict when generating a parser ( I am using CUP ).
you can solve this problem by two ways. ( or you can re-define the if-else grammar rule with unambiguous if-else rules. I am working on it, hope to update this post after it)
1) adding precedence ELSE:
eg: modify code as given bellow.
selection_stmt ::= IF '(' expression ')' statement | IF '(' expression ')' statement ELSE statement ;
This is a "Dangling else" problem that leads to Shift/Reduce conflict when generating a parser ( I am using CUP ).
Warning : *** Shift/Reduce conflict found in state #72 between selection_stmt ::= IF '(' expression ')' statement (*) and selection_stmt ::= IF '(' expression ')' statement (*) ELSE statement under symbol ELSE Resolved in favor of shifting.
you can solve this problem by two ways. ( or you can re-define the if-else grammar rule with unambiguous if-else rules. I am working on it, hope to update this post after it)
1) adding precedence ELSE:
eg: modify code as given bellow.
precedence left PLUS, MINUS; precedence left TIMES, DIVIDE; precedence left ELSE;
2) Allow to resolve in favor of shifting:
you can generate parser code expecting 1(or more) shift/reduce conflict.
eg: add "-expect 1" option to tell expect one shift/reduce conflict.
cup -expect 1 -parser CMinusParser cminus.cup
