I developed this small grammar here i have an issue with:
grammar test;
term : above_term | below_term;
above_term :
<assoc=right> 'forall' binders ',' forall_term
| <assoc=right> above_term '->' above_term
| <assoc=right> above_term '->' below_term
| <assoc=right> below_term '->' above_term
| <assoc=right> below_term '->' below_term
;
below_term :
<assoc = right> below_term arg (arg)*
| '@' qualid (term)*
| below_term '%' IDENT
| qualid
| sort
| '(' term ')'
;
forall_term : term;
arg : term| '(' IDENT ':=' term ')';
binders : binder (binder)*;
binder : name |<assoc=right>name (name)* ':' term | '(' name (name)* ':' term ')' |<assoc=right> name (':' term)? ':=' term;
name : IDENT | '_';
qualid : IDENT | qualid ACCESS_IDENT;
sort : 'Prop' | 'Set' | 'Type' ;
/**************************************
* LEXER RULES
**************************************/
/*
* STRINGS
*/
STRING : '"' (~["])* '"';
/*
* IDENTIFIER AND ACCESS IDENTIFIER
*/
ACCESS_IDENT : '.' IDENT;
IDENT : FIRST_LETTER (SUBSEQUENT_LETTER)*;
fragment FIRST_LETTER : [a-z] | [A-Z] | '_' | UNICODE_LETTER;
fragment SUBSEQUENT_LETTER : [a-z] | [A-Z] | DIGIT | '_' | '"' | UNICODE_LETTER | UNICODE_ID_PART;
fragment UNICODE_LETTER : '\\' 'u' HEX HEX HEX HEX;
fragment UNICODE_ID_PART : '\\' 'u' HEX HEX HEX HEX;
fragment HEX : [0-9a-fA-F];
/*
* NATURAL NUMBERS AND INTEGERS
*/
NUM : DIGIT (DIGIT)*;
INTEGER : ('-')? NUM;
fragment DIGIT : [0-9];
WS : [ \n\t\r] -> skip;
You can copy this grammar and test it with antlr if you want, it will work. Now for my question: Let's consider an expression like this: ab -> cd -> forall n:nat, c . Now according to my grammar the ("->") rule (right after forall rule) has the highest precedence. As for this I want this term to be parsed so that both ("->") rules are on top of the parse tree. like this: (Please note, that this is an abstract view, i know that there are many above and below terms between the leafs)
However sadly it doesn't get parsed this way but this way:
Howcome the parser doesn't see the (->) rules both on top of the parse tree? Is this a precedence issue?
By changing term to below_term in the ( arg ) rule we can fix the problem arg : below_term| '(' IDENT ':=' term ')';
arg : below_term| '(' IDENT ':=' term ')';
.
Lets take this expression as an example: abc
. Once the parser sees, that the pattern ab
matches this rule: below_term arg (arg)*
he puts a as a below_term and trys to match b with the arg rule. However since arg points to the below_term rule now, no above_term is alowed except when it is braced. This solved my problem.
The term ab -> abc -> forall n:nat, n
now gets parsed this way:
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