//parserr.y
//tokens
---------
/* precedences */
%left T_LPAREN T_RPAREN
%left T_MULOP T_DIVOP
%left T_ADDOP
%left T_ANDOP
%left T_OROP
%left T_NOTOP
%right T_POWEROP
%right T_ASSIGN
%nonassoc T_RELOP
%nonassoc T_PAIROP
%start program
** syntax rules - same file **
program: body T_END subprograms
;
body: declarations statements
;
declarations: declarations couplespec type vars
| declarations T_DATA vals
| %empty { }
;
couplespec: T_COUPLE
| %empty { }
;
type: T_INTEGER
| T_REAL
| T_LOGICAL
| T_CHARACTER
;
vars: vars T_COMMA undef_variable
| undef_variable
;
undef_variable: T_ID T_LPAREN dims T_RPAREN
| T_ID
;
dims: dims T_COMMA dim
| dim
;
dim: T_ICONST
| T_ID
;
vals: vals T_COMMA T_ID value_list
| T_ID value_list
;
value_list: T_DIVOP values T_DIVOP
;
values: values T_COMMA value
| value
;
value: repeat T_MULOP T_ADDOP simp_constant
| repeat T_MULOP constant
| repeat T_MULOP T_STRING
| T_ADDOP simp_constant
| constant
| T_STRING
;
repeat: T_ICONST
| %empty { }
;
simp_constant: T_ICONST
| T_RCONST
| T_LCONST
| T_CCONST
;
constant: simp_constant
| coup_constant
;
coup_constant: T_LPAREN simp_constant T_COLON simp_constant T_RPAREN
| T_LPAREN simp_constant T_COLON T_ADDOP simp_constant T_RPAREN
| T_LPAREN T_ADDOP simp_constant T_COLON simp_constant T_RPAREN
| T_LPAREN T_ADDOP simp_constant T_COLON T_ADDOP simp_constant T_RPAREN
;
statements: statements labeled_statement
| labeled_statement
;
labeled_statement: label statement
| statement
;
label: T_ICONST
;
statement: simple_statement
| compound_statement
;
simple_statement: assignment
| goto_statement
| if_statement
| subroutine_call
| io_statement
| T_CONTINUE
| T_RETURN
| T_STOP
;
assignment: variable T_ASSIGN expression
| variable T_ASSIGN T_STRING
;
variable: variable T_LPAREN expressions T_RPAREN
| T_ID
;
expressions: expressions T_COMMA expression
| expression
;
expression: expression T_OROP expression
| expression T_ANDOP expression
| expression T_RELOP expression
| expression T_ADDOP expression
| expression T_MULOP expression
| expression T_DIVOP expression
| expression T_POWEROP expression
| T_NOTOP expression
| T_ADDOP expression
| T_PAIROP expression
| variable
| constant
| T_LPAREN expression T_COLON expression T_RPAREN
| T_LPAREN expression T_RPAREN
;
goto_statement: T_GOTO label
| T_GOTO T_ID T_COMMA T_LPAREN labels T_RPAREN
;
labels: labels T_COMMA label
| label
;
if_statement: T_IF T_LPAREN expression T_RPAREN label T_COMMA label T_COMMA label
| T_IF T_LPAREN expression T_RPAREN simple_statement
| T_IF error expression T_RPAREN simple_statement
| T_IF T_LPAREN expression error simple_statement
;
subroutine_call: T_CALL variable
;
io_statement: T_READ read_list
| T_WRITE write_list
;
read_list: read_list T_COMMA read_item
| read_item
;
read_item: variable
| T_LPAREN read_list T_COMMA T_ID T_ASSIGN iter_space T_RPAREN
;
iter_space: expression T_COMMA expression step
;
step: T_COMMA expression
| %empty { }
;
write_list: write_list T_COMMA write_item
| write_item
;
write_item: expression
| T_LPAREN write_list T_COMMA T_ID T_ASSIGN iter_space T_RPAREN
| T_STRING
;
compound_statement: branch_statement
| loop_statement
;
branch_statement: T_IF T_LPAREN expression T_RPAREN T_THEN body tail
;
tail: T_ELSE body T_ENDIF
| T_ENDIF
;
loop_statement: T_DO T_ID T_ASSIGN iter_space body T_ENDDO
;
subprograms: subprograms subprogram
| %empty { }
;
subprogram: header body T_END
;
header: type T_FUNCTION T_ID T_LPAREN formal_parameters T_RPAREN
| T_SUBROUTINE T_ID T_LPAREN formal_parameters T_RPAREN
| T_SUBROUTINE T_ID
;
formal_parameters: type vars T_COMMA formal_parameters
| type vars
;
(FILE: parserr.output)
State 87 conflicts: 1 shift/reduce
State 124 conflicts: 1 shift/reduce
(State 87 ):
State 87
37 constant: simp_constant .
39 coup_constant: "(" simp_constant . ":" simp_constant ")"
40 | "(" simp_constant . ":" "+ -" simp_constant ")"
":" shift, and go to state 125
":" [reduce using rule 37 (constant)]
$default reduce using rule 37 (constant)
(State 124):
State 124
37 constant: simp_constant .
41 coup_constant: "(" "+ -" simp_constant . ":" simp_constant ")"
42 | "(" "+ -" simp_constant . ":" "+ -" simp_constant ")"
":" shift, and go to state 159
":" [reduce using rule 37 (constant)]
$default reduce using rule 37 (constant)
I am getting 2 shift/reduce conflicts, i tried using %prec XXX in the end but it did not work. I also tried defining colon ":" with left precedence, it didnt work either.
Your grammar has an ambiguity in the rules for expression:
expression: T_LPAREN expression T_COLON expression T_RPAREN
expression: constant
with
constant: coup_constant
coup_constant: T_LPAREN simp_constant T_COLON simp_constant T_RPAREN
(1,2) can be produced through either of these, resulting in the conflict.
The simplest resolution would be to replace expression: constant with expression: simp_constant, forcing the parser to accept the more general option.
Trying to use the constant interpretation when possible will make it impossible to correctly parse (2:a), which is a valid expression, because the parser needs to decide before a is the lookahead. For the same reason, you cannot readily solve this conflict with a precedence declaration.
That might or might not conform to your semantic requirements, but you could transform the constant in the semantic action were that necessary.