CODEWITHSUNDEEP
antlr4
wied
wied

Reputation: 1

Antlr4: extraneous input in antlr4

I have problem running input stream for my grammar, here is part of my grammar

expression  
:  .... 
|   ( '+' | '-' | '&' |) expression
|   expression ('+'|'-') expression
   ....
;

when input stream like 2+2-2 or (2+2+2)-2, error occurs 

line 10:30 extraneous input '-2' expecting {',', '^',...}

why my grammar can not distinguish between -2 and 2-2 ? anyone help me please !

Upvotes: 0

Views: 660

Answers (1)

Sam Harwell
Sam Harwell

Reputation: 99869

It appears that you have written your lexer in such a way that -2 results in a single token. Instead of handling negative numbers in this way, treat - as a unary operator and allow your parser handle the negation operation. If you try to handle negative numbers directly in the lexer, input such as 2-2 will be sent to the parser as 2 consecutive number tokens (2 followed by -2) instead of the desired 3 tokens (2, -, 2).

Upvotes: 2

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