Question

I’m using ANTRL and this is my some grammar which give error to me.

statement
:     (name)(
    | BECOMES expression
    | LPAREN (expression (COMMA expression)*)? RPAREN
    | SHIFTLEFT name LPAREN (expression ( COMMA expression )*)? RPAREN
    )
    | OUTPUT LPAREN expression ( COMMA expression)* RPAREN
    | IF expression  THEN statement (ELSE statement)?
    | FOR name BECOMES expression TO expression DO statement
    | REPEAT statement UNTIL expression
    | WHILE expression DO statement
    | body
    | 
;

This is error ” Decision can match input such as “ELSE” using multiple alternatives “.

How can I fix it ?

Answer 1

Try using the backtrack option.

options {
    backtrack = true;
}

Description

The new feature (a big one) is the
backtrack=true option for grammar,
rule, and block that lets you type in
any old crap and ANTLR will backtrack
if it can’t figure out what you meant.
No errors are reported by antlr during
analysis. It implicitly adds a syn
pred in front of every production,
using them only if static grammar LL*
analysis fails. Syn pred code is not
generated if the pred is not used in a
decision. This is essentially a rapid
prototyping mode. It is what I have
used on the java.g. Oh, it doesn’t
memoize partial parses (i.e. rule
parsing results) during backtracking
automatically now. You must also say
memoize=true. Can make a HUGE
difference to turn on.