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perl/Examples/Chap2/rpn-ifelse

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+
+
+###
+### rpn_ifelse
+###
+
+## Chapter 2 section 2
+
+my $result = evaluate($ARGV[0]);
+print "Result: $result\n";
+
+sub evaluate {
+  my @stack;
+  my ($expr) = @_;
+  my @tokens = split /\s+/, $expr;
+  for my $token (@tokens) {
+    if ($token =~ /^\d+$/) {   # It's a number
+      push @stack, $token;
+    } elsif ($token eq '+') {
+       push @stack, pop(@stack) + pop(@stack);
+    } elsif ($token eq '-') {
+       my $s = pop(@stack);
+       push @stack, pop(@stack) - $s
+    } elsif ($token eq '*') {
+       push @stack, pop(@stack) * pop(@stack);
+    } elsif ($token eq '/') {
+       my $s = pop(@stack);
+       push @stack, pop(@stack) / $s
+    } else {
+      die "Unrecognized token `$token'; aborting";
+    }
+   }
+  return pop(@stack);
+}