...
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$ perl t.pl 2 + 2 4 |
2007-08-08
+ Simple expression grammar
The grammar
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grammar Expr;
options {
language = Perl5;
}
@header {
}
@members {
my %memory;
}
prog: stat+ ;
stat: expr NEWLINE { print "$expr.value\n"; }
| ID '=' expr NEWLINE
{ $memory{$ID.text} = $expr.value; }
| NEWLINE
;
expr returns [value]
: e=multExpr { $value = $e.value; }
( '+' e=multExpr { $value += $e.value; }
| '-' e=multExpr { $value -= $e.value; }
)*
;
multExpr returns [value]
: e=atom { $value = $e.value; } ('*' e=atom { $value *= $e.value; })*
;
atom returns [value]
: INT { $value = $INT.text; }
| ID
{
my $v = $memory{$ID.text};
if (defined $v) {
$value = $v;
} else {
print STDERR "undefined variable $ID.text\n";
}
}
| '(' expr ')' { $value = $expr.value; }
;
ID : ('a'..'z'|'A'..'Z')+ ;
INT : '0'..'9'+ ;
NEWLINE:'\r'? '\n' ;
WS : (' '|'\t')+ { $self->skip(); } ;
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Test program
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#!/usr/bin/perl
use strict;
use warnings;
use blib '../..';
use ANTLR::Runtime::ANTLRStringStream;
use ANTLR::Runtime::CommonTokenStream;
use ExprLexer;
use ExprParser;
my $in;
{
undef $/;
$in = <>;
}
my $input = ANTLR::Runtime::ANTLRStringStream->new($in);
my $lexer = ExprLexer->new($input);
my $tokens = ANTLR::Runtime::CommonTokenStream->new({ token_source => $lexer });
my $parser = ExprParser->new($tokens);
$parser->prog();
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Test run
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$ perl t.pl
x=1
y=2
3*(x+y)
^Z
9
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Author
Ronald Blaschke (ron at rblasch org)