Firstly, I have already referred to many similar questions here, but unable to resolve the conflicts.
I have this piece in my .y file
.
.
.
obj
: INT { $$ = objNew($1, INT_T); }
| FLOAT { $$ = objNew($1, FLOAT_T); }
| STR { $$ = objNew($1, STR_T); }
;
var
: IDEN { $$ = varLookup($1); }
;
atom
: '(' expression ')' { $$ = $2; }
;
index
: '[' obj ']' { $$ = $2; }
;
primary_expr
: obj { $$ = objExpr($1); }
| var { $$ = varExpr($1); }
| atom { $$ = atmExpr($1); }
| expression index { $$ = idxExpr($1, $2); }
;
unary_expr
: primary_expr { $$ = $1; }
| '+' unary_expr { $$ = unExpr(UPLUS, $2); }
| '-' unary_expr { $$ = unExpr(UMINUS, $2); }
;
power_expr
: unary_expr { $$ = $1; }
| power_expr '^' unary_expr { $$ = biExpr('^', $1, $3); }
;
multiplicative_expr
: power_expr { $$ = $1; }
| multiplicative_expr '*' power_expr { $$ = biExpr('*', $1, $3); }
| multiplicative_expr '/' power_expr { $$ = biExpr('/', $1, $3); }
;
additive_expr
: multiplicative_expr { $$ = $1; }
| additive_expr '+' multiplicative_expr { $$ = biExpr('+', $1, $3); }
| additive_expr '-' multiplicative_expr { $$ = biExpr('-', $1, $3); }
;
relational_expr
: additive_expr { $$ = $1; }
| relational_expr '>' additive_expr { $$ = biExpr('>', $1, $3); }
| relational_expr '<' additive_expr { $$ = biExpr('<', $1, $3); }
| relational_expr '=' additive_expr { $$ = biExpr('=', $1, $3); }
;
referential_expr
: relational_expr { $$ = $1; }
| referential_expr IS relational_expr { $$ = biExpr(IS, $1, $3); }
;
conjunction_expr
: referential_expr { $$ = $1; }
| conjunction_expr AND referential_expr { $$ = biExpr(AND, $1, $3); }
;
disjunction_expr
: conjunction_expr { $$ = $1; }
| disjunction_expr OR conjunction_expr { $$ = biExpr(OR, $1, $3); }
;
conditional_expr
: disjunction_expr { $$ = $1; }
| disjunction_expr '?' disjunction_expr ':' conditional_expr { $$ = trExpr('?', $1, $3, $5); }
;
sequence
: conditional_expr { $$ = seqChain(NULL, $1); }
| sequence ',' conditional_expr { $$ = seqChain($1, $3); }
;
assignment_expr
: sequence { $$ = seqAssign($1, NULL); }
| sequence ASS assignment_expr { $$ = seqAssign($1, $3); }
;
expression
: assignment_expr { $$ = $1; }
;
statement
: ';' { $$ = NULL; }
| expression ';' { $$ = exprStmt($1); }
;
routine
: routine statement { $$ = rtnChain($1, $2); }
| { $$ = NULL; }
;
program
: routine { compile($1); exit(0); }
;
.
.
.
This grammer is producing lots of reduce\reduce conflicts. Eg:
State 81
18 power_expr: unary_expr .
19 | power_expr '^' unary_expr .
'+' reduce using rule 18 (power_expr)
'+' [reduce using rule 19 (power_expr)]
I have lots of conflicts exactly similar to this. But I'm failing to understand this.
According to my knowledge, it is saying that, when the production is unary_expr
or when it is power_expr '^' unary_expr
and then it looks a '+'
, it is facing a reduce\reduce conflict. But why there is a reduce\reduce conflict? When it has power_expr '^'
part, it can use rule 19 (and should use since otherwise production will be power_expr '^' power_expr
which is not defined in grammer.) and when does not have power_expr '^'
part, it has to use rule 18. Where does the ambiguity arises here, and how to resolve it.
The problem stems from the rule
primary_expr: expression index
That rule cannot be correct, since it implies that a+b[3]
could be parsed by applying the [3]
to the expression
a+b
. But it could also be parsed as though written a+(b[3])
. This ambiguity produces the reduce-reduce conflicts.
We know that only the second interpretation is correct, which strongly suggests that the rule should be
primary_expr: primary_expr index
I believe that change will resolve your conflicts.