Antlr grammar for parsing simple expression - antlr

Question

I would like to parse following expresion with antlr4
termspannear ( xxx, xxx , 5 , true )
termspannear ( xxx, termspannear ( xxx, xxx , 5 , true ) , 5 , true )
Where termspannear functions can be nested
Here is my grammar:
//Define a gramar to parse TermSpanNear
grammar TermSpanNear;
start : TERMSPAN ;
TERMSPAN : TERMSPANNEAR | 'xxx' ;
TERMSPANNEAR: 'termspannear' OPENP BODY CLOSEP ;
BODY : TERMSPAN COMMA TERMSPAN COMMA SLOP COMMA ORDERED ;
COMMA : ',' ;
OPENP : '(' ;
CLOSEP : ')' ;
SLOP : [0-9]+ ;
ORDERED : 'true' | 'false' ;
WS : [ \t\r\n]+ -> skip ; // skip spaces, tabs, newlines
After running:
antlr4 TermSpanNear.g4
javac TermSpanNear*.java
grun TermSpanNear start -gui
termspannear ( xxx, xxx , 5 , true )
^D![enter image description here][1]
line 1:0 token recognition error at: 'termspannear '
line 1:13 extraneous input '(' expecting TERMSPAN
and the tree looks like:
Can someone help me with this grammar ?
So the parsed tree contains all params and and also nesting works
NOTE:
After suggestion by I rewrote it to
//Define a gramar to parse TermSpanNear
grammar TermSpanNear;
start : termspan EOF;
termspan : termspannear | 'xxx' ;
termspannear: 'termspannear' '(' body ')' ;
body : termspan ',' termspan ',' SLOP ',' ORDERED ;
SLOP : [0-9]+ ;
ORDERED : 'true' | 'false' ;
WS : [ \t\r\n]+ -> skip ; // skip spaces, tabs, newlines
I think now it works
I'm geting the following trees:
For
termspannear ( xxx, xxx , 5 , true )
For
termspannear ( xxx, termspannear ( xxx, xxx , 5 , true ) , 5 , true )

Answer 1

You're using way too many lexer rules.
When you're defining a token like this:
BODY : TERMSPAN COMMA TERMSPAN COMMA SLOP COMMA ORDERED ;
then the tokenizer (lexer) will try to create the (single!) token: xxx,xxx,5,true. E.g. it does not allow any space in between it. Lexer rules (the ones starting with a capital) should really be the "atoms" of your language (the smallest parts). Whenever you start creating elements like a body, you glue atoms together in parser rules, not in lexer rules.
Try something like this:
grammar TermSpanNear;
// parser rules (the elements)
start : termpsan EOF ;
termpsan : termpsannear | 'xxx' ;
termpsannear : 'termspannear' OPENP body CLOSEP ;
body : termpsan COMMA termpsan COMMA SLOP COMMA ORDERED ;
// lexer rules (the atoms)
COMMA : ',' ;
OPENP : '(' ;
CLOSEP : ')' ;
SLOP : [0-9]+ ;
ORDERED : 'true' | 'false' ;
WS : [ \t\r\n]+ -> skip ;