How to translate the yacc rule into pest grammar

[jbmwdzg]

I am working on the C pest grammar development by referring to the ANSI C Yacc grammar. Just have a question
For this rule in yacc
postfix_expression
: primary_expression
| postfix_expression '[' expression ']'
| postfix_expression '(' ')'
| postfix_expression '(' argument_expression_list ')'
| postfix_expression '.' IDENTIFIER
| postfix_expression PTR_OP IDENTIFIER
| postfix_expression INC_OP
| postfix_expression DEC_OP

How can I translate into pest, the difficulty is how to resolve the left recursive?

Really appreciate!

[jbmwdzg]

It is very important for me to move forward, anyone can share the idea? thanks

[tomtau]

How about this:

postfix_expression = { primary_expression ~ postfix_expression_part* }
postfix_expression_part = _{
    "[" ~ expression ~ "]"
    | "(" ~ ")" 
    | "(" ~ argument_expression_list ~ ")"
    | "." ~ IDENTIFIER 
    | PTR_OP ~ IDENTIFIER
    | INC_OP
    | DEC_OP
}

[jbmwdzg]

@tomtau Really thanks. I will validate it

[jbmwdzg]

@tomtau One more case, would you kindly advise as well?
direct_abstract_declarator
: '(' abstract_declarator ')'
| '[' ']'
| '[' constant_expression ']'
| direct_abstract_declarator '[' ']'
| direct_abstract_declarator '[' constant_expression ']'
| '(' ')'
| '(' parameter_type_list ')'
| direct_abstract_declarator '(' ')'
| direct_abstract_declarator '(' parameter_type_list ')'
;

[jbmwdzg]

I follow your idea to write down the rule as below

direct_abstract_declarator = {
("(" ~ abstract_declarator ~ ")" | "[" ~ "]" | "[" ~ constant_expression ~ "]" | "(" ~ ")" | "(" ~ parameter_type_list ~ ")") ~ direct_abstract_declarator_part*
}

direct_abstract_declarator_part = _{
"[" ~ "]"
| "[" ~ "constant_expression " ~ "]"
| "(" ~ ")"
| "(" ~ parameter_type_list ~ ")"
}
Still feel something wrong about it, do you have any comments? thanks

[tomtau]

1. the way you’ve written the rule, you expect the direct_abstract_declarator to start with a certain pattern (like "(" ~ abstract_declarator ~ ")" or "[" ~ "]" etc.), and then follow with zero or more direct_abstract_declarator_part. But in the direct_abstract_declarator_part, you repeated some patterns that have already been considered in the direct_abstract_declarator.

2. you’ve enclosed "constant_expression " within quotes, which makes it a string literal. I assume constant_expression is another rule in your grammar?

[jbmwdzg]

1. the way you’ve written the rule, you expect the direct_abstract_declarator to start with a certain pattern (like "(" ~ abstract_declarator ~ ")" or "[" ~ "]" etc.), and then follow with zero or more direct_abstract_declarator_part. But in the direct_abstract_declarator_part, you repeated some patterns that have already been considered in the direct_abstract_declarator.
2. you’ve enclosed "constant_expression " within quotes, which makes it a string literal. I assume constant_expression is another rule in your grammar?

Thanks @tomtau for valuable comments.
For point 1, may I understand that if I remove the duplicated part from direct_abstract_declarator_part rule, for example, "[" ~ "]", which I have defined in the direct_abstract_declarator , should it accomplish the same purpose as the one in yacc grammar, rt?

For point 2, you are right, it is my mistake, constant_expression is a rule

[jbmwdzg]

I re-defined the rule as below

*direct_abstract_declarator = {
"(" ~ abstract_declarator ~ ")" ~ direct_abstract_declarator_part
}

direct_abstract_declarator_part = _{
"[" ~ "]"
| "[" ~ constant_expression ~ "]"
| "(" ~ ")"
| "(" ~ parameter_type_list ~ ")"
}**

Hope I have correctly understood your comments, ^o^