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+package Ast;
+use strict;
+
+use vars qw/ $this $pack @endCodes /;
+
+#-----------------------------------------------------------------------------
+# This package is used to create a simple Abstract Syntax tree. Each node
+# in the AST is an associative array and supports two kinds of properties -
+# scalars and lists of scalars.
+# See SchemParser.pm for an example of usage.
+# ... Sriram
+#-----------------------------------------------------------------------------
+
+# Constructor
+# e.g AST::New ("personnel")
+# Stores the argument in a property called astNodeName whose sole purpose
+# is to support Print()
+
+sub New {
+ my ($this) = {"astNodeName" => $_[0]};
+ bless ($this);
+ return $this;
+}
+
+# Add a property to this object
+# $astNode->AddProp("className", "Employee");
+
+sub AddProp {
+ my ($this) = $_[0];
+ $this->{$_[1]} = $_[2];
+}
+
+# Equivalent to AddProp, except the property name is associated
+# with a list of values
+# $classAstNode->AddProp("attrList", $attrAstNode);
+
+sub AddPropList {
+ my ($this) = $_[0];
+ if (! exists $this->{$_[1]}) {
+ $this->{$_[1]} = [];
+ }
+ push (@{$this->{$_[1]}}, $_[2]);
+}
+
+# Returns a list of all the property names of this object
+sub GetProps {
+ my ($this) = $_[0];
+ return keys %{$this};
+}
+
+sub Visit {
+ # Converts each of this AstNode's properties into global variables.
+ # The global variables are introduced into package "main"
+ # At the same time, a piece of code is formed to undo this work above -
+ # $endCode essentially contains the values of these global variables
+ # before they are mangled. endCode gets pushed into a stack (endCodes),
+ # which is unwound by UnVisit().
+
+ local ($this, $pack) = @_;
+
+
+ my $code = "";
+ my $endCode = "";
+
+
+ foreach my $k (keys %{$this}) {
+
+ my $glob = $pack."::".$k;
+
+ if ( defined $$glob ) {
+
+ if ( ${$glob} ne "" ) {
+ $$glob =~ s/\'/\\\'/g;
+ }
+
+ $endCode .= '$'.$pack.'::'.$k. " = '".$$glob."';";
+ } else {
+ $endCode .= '$'.$pack . "::". $k . ' = "";';
+ }
+ $code .= '$'.$pack . "::" . $k . "= \$this->{\"$k\"};";
+ }
+ push (@endCodes, $endCode);
+ eval($code) if $code;
+}
+
+sub UnVisit {
+ my $code = pop(@endCodes);
+ eval($code) if ($code);
+}
+
+1;