I'm implementing a BASIC-like language, the syntax of if statements is
almost the same to BASIC:
IF a == b THEN
PRINT "EQUAL"
ELSE
PRINT "UNEQUAL"
ENDIF
I have write a grammar file to parse and a tree walker to interpreter the
language:
[Expr.g]
options {
language=Python;
output=AST;
ASTLabelType=CommonTree;
}
tokens {
BLOCK;
}
block
: stmt* -> ^(BLOCK stmt*)
;
if_stmt
: 'IF' c=expr 'THEN' t=block ('ELSE' f=block)? 'ENDIF'
-> ^('IF' $c $t+ ^('ELSE' $f+))
;
In the AST walker:
[Walker.g]
options {
language=Python;
tokenVocab=Expr;
ASTLabelType=CommonTree;
}
block
: ^(BLOCK stmt*)
;
stmt
: ...
| 'IF' expr t=stmt* 'ELSE' f=stmt*
{}
Now I can correctly generate AST for my language, but I don't know how to
handle branch statement. To be more exactly, if the *expr* in if statement
is true, how can I avoid evaluation of the ELSE statement? Thanks
--
Best regards,
Wang Yuanxuan
Parallel Processing Institute, Fudan University
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