1 files changed, 55 insertions, 0 deletions
diff --git a/runtime/Ruby/lib/antlr3/debug/rule-tracer.rb b/runtime/Ruby/lib/antlr3/debug/rule-tracer.rb
new file mode 100644
index 0000000..f1e2b5f
--- /dev/null
+++ b/runtime/Ruby/lib/antlr3/debug/rule-tracer.rb
@@ -0,0 +1,55 @@
+#!/usr/bin/ruby
+# encoding: utf-8
+
+module ANTLR3
+module Debug
+=begin rdoc ANTLR3::Debug::RuleTracer
+
+RuleTracer is simple debug event listener that writes the names of rule methods
+as they are entered and exitted to an output stream.
+
+=end
+class RuleTracer
+  include EventListener
+  
+  ARROW_IN = '--> '.freeze
+  ARROW_OUT = '<-- '.freeze
+  
+  attr_reader :level
+  attr_accessor :spaces_per_indent, :device
+  
+  def initialize( options = {} )
+    @input = options[ :input ]
+    @level = 0
+    @spaces_per_indent = options[ :spaces_per_indent ] || 2
+    @device = options[ :device ] || options[ :output ] || $stderr
+  end
+  
+  def enter_rule( grammar_file, name )
+    indent = @level * @spaces_per_indent
+    
+    @device.print( ' ' * indent, ARROW_IN, name )
+    if @input
+      input_symbol = @input.look || :EOF
+      @device.puts( " look = %p" % input_symbol )
+    else @device.print( "\n" )
+    end
+    
+    @level += 1
+  end
+  
+  def exit_rule( grammar_file, name )
+    @level -= 1
+    
+    indent = @level * @spaces_per_indent
+    
+    @device.print( ' ' * indent, ARROW_OUT, name )
+    if @input
+      input_symbol = ( @input.look || :EOF )
+      @device.puts( " look = %p" % input_symbol )
+    else @device.print( "\n" )
+    end
+  end
+end
+end
+end