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perl/Examples/Chap8/expr-parser-2.pl

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+
+
+###
+### simple-expr-parser-2.pl
+###
+
+## Chapter 8 section 4
+
+use Parser ':all';
+use Lexer ':all';
+
+my ($expression, $term, $factor);
+my $Expression = parser { $expression->(@_) };
+my $Term       = parser { $term      ->(@_) };
+my $Factor     = parser { $factor    ->(@_) };
+$expression = alternate(concatenate($Term,
+                                    lookfor(['OP', '+']),
+                                    $Expression),
+                        $Term);
+
+$term       = alternate(concatenate($Factor,
+                                    lookfor(['OP', '*']),
+                                    $Term),
+                        $Factor);
+
+$factor     = alternate(lookfor('INT'),
+                        concatenate(lookfor(['OP', '(']),
+                                    $Expression,
+                                    lookfor(['OP', ')']))
+                        );
+
+$entire_input = concatenate($Expression, \&End_of_Input);