Initial import.

.gitignore

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+.DS_Store

parse_tree.rb

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+# make an "e" method to evaluate a parse tree
+# make a "q" method to quote a parse tree
+# make a "p" method to create a new parse tree
+
+class ParseTree
+  def initialize(nodes)
+    @nodes = nodes
+  end  
+  attr_accessor :nodes
+  def evaluate(array = nodes)
+    node_method = array.first.keys.first.to_sym
+    node_object = if array.first.values.first.is_a?(Array)
+      evaluate(array.first.values.first)
+    else
+      array.first.values.first
+    end
+    node_arguments = []
+    array.rest.each do |element|
+      node_arguments << if element.is_a?(Array)
+        evaluate(element)          
+      else
+        element
+      end
+    end
+    node_object.send( *([node_method] + node_arguments) )
+  end
+end
+
+class Array
+  def rest
+    self[1..size]
+  end
+end

spec/parse_tree_spec.rb

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+require File.join(File.dirname(__FILE__), "..", "parse_tree")
+
+describe ParseTree, "#nodes" do  
+  it "should raise an Exception if not initialized" do
+    lambda {ParseTree.new}.should raise_error
+  end
+
+  it "should return an arary of nodes when initialized" do
+    ParseTree.new([{:+ => 1}, 2]).nodes.should == [{:+ => 1}, 2]
+  end
+
+  it "should be able to add nodes" do
+    parse_tree = ParseTree.new([{:+ => 1}])
+    parse_tree.nodes << 2
+    parse_tree.nodes.should == [{:+ => 1}, 2]
+  end
+end
+
+describe ParseTree, "#evaluate, with terminal parameters and objects" do
+  it "should be able to evaluate an expression for a parse tree with no parameters" do
+    parse_tree = ParseTree.new( [{:to_s => 1}] )            
+    parse_tree.evaluate.should == "1"
+  end
+
+  it "should be able to evaluate an expression for a parse tree with a parameter" do
+    parse_tree = ParseTree.new( [{:+ => 1}, 2] )            
+    parse_tree.evaluate.should == 3
+  end
+
+  it "should be able to evaluate an expression for a parse tree with multiple parameters" do
+    parse_tree = ParseTree.new( [{:new => Array}, 2, 1] )            
+    parse_tree.evaluate.should == [1, 1]
+  end
+end
+
+describe ParseTree, "#evaluate, with function parameters" do
+  it "should be able to evaluate an expression for a simple parse tree" do
+    parse_tree = ParseTree.new( [ {:+ => 1}, [{:* => 2}, 2] ] )            
+    parse_tree.evaluate.should == 5
+  end
+
+  it "should be able to evaluate an expression for a complex parse tree" do
+    parse_tree = ParseTree.new( [ {:+ => 2}, [{:+ => 1}, [{:* => 2}, 2]] ] )                
+    parse_tree.evaluate.should == 7
+  end
+end
+
+describe ParseTree, "#evaluate, with function objects" do
+  it "should be able to evaluate an expression for a simple parse tree" do
+    parse_tree = ParseTree.new( [ {:+ => 1}, [{:* => 2}, 2] ] )            
+    parse_tree.evaluate.should == 5
+  end
+
+  it "should be able to evaluate an expression for a complex parse tree" do
+    parse_tree = ParseTree.new( [ {:+ => 2}, [{:+ => 1}, [{:* => 2}, 2]] ] )                
+    parse_tree.evaluate.should == 7
+  end
+end
+
+describe ParseTree, "#evaluate, for complex mixed parameters" do
+  it "should be able to evaluate" do
+    parse_tree = ParseTree.new( 
+      [{:+ => [{:+ => 1}, 2]}, 
+        [{:+ => [{:+ => 1}, 2]}, 
+          [{:* => [{:+ => 1}, 2]}, 
+            [{:+ => 1}, 2]]]] 
+    )           
+    parse_tree.evaluate.should == 15
+  end
+end