CODEWITHSUNDEEP
parsingantlr4left-recursion
sara
sara

Reputation: 91

How to modify grammar to remove left recursive error in ANTLR4?

I'm trying to parse a language. The follow ANTLR4 parser rules are directly copied from the language specification :

physical_value 
 : raw_value DIV factor MUL factor PLUS offset 
 ;

raw_value
 : (physical_value MINUS offset) DIV factor  
 ;

but antlr reports an error:The following sets of rules are mutually left-recursive I don't know how to modify the grammar, Hope someone can help me. Thanks.

Upvotes: 0

Views: 360

Answers (1)

Sam Harwell
Sam Harwell

Reputation: 99859

You cannot eliminate the left recursion from the rules you posted, because the only string it matches is an infinite sequence.

  • physical_value always starts with a raw_value
  • raw_value always starts with a physical_value

...and repeat

Upvotes: 1

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