Add failing specs for Set#one?

Implement List#group_by.

lib/hamster/list.rb

@@ -2,6 +2,7 @@
 require 'monitor'
 
 require 'hamster/tuple'
+require 'hamster/hash'
 require 'hamster/set'
 
 module Hamster
@@ -43,6 +44,10 @@ module List
 
     extend Forwardable
 
+    Undefined = Object.new
+
+    CADR = /^c([ad]+)r$/
+
     def_delegator :self, :head, :first
 
     def_delegator :self, :empty?, :null?
@@ -478,16 +483,20 @@ def inspect
       to_a.inspect
     end
 
+    def group_by(&block)
+      return group_by { |item| item } unless block_given?
+      reduce(Hamster::Hash.new) do |hash, item|
+        key = yield(item)
+        hash.put(key, (hash.get(key) || EmptyList).cons(item))
+      end
+    end
+
     def respond_to?(name, include_private = false)
       super || CADR === name
     end
 
     private
 
-    Undefined = Object.new
-
-    CADR = /^c([ad]+)r$/
-
     def method_missing(name, *args, &block)
       if CADR === name
         accessor($1)

lib/hamster/set.rb

@@ -116,6 +116,10 @@ def none?
       true
     end
 
+    def one?
+      return one? { |item| item } unless block_given?
+    end
+
     def find
       return nil unless block_given?
       each { |item| return item if yield(item) }

lib/hamster/trie.rb

@@ -91,7 +91,7 @@ def include?(key, value)
 
     # Returns <tt>true</tt> if . <tt>eql?</tt> is synonymous with <tt>==</tt>
     def eql?(other)
-      return true if other.equal?(self)
+      # return true if other.equal?(self)
       return false unless other.is_a?(self.class) && other.size == size
       each do |entry|
         return false unless other.include?(entry.key, entry.value)

spec/hamster/list/group_by_spec.rb

@@ -0,0 +1,73 @@
+require File.expand_path(File.dirname(__FILE__) + '/../../spec_helper')
+
+require 'hamster/list'
+
+describe Hamster::List do
+
+  describe "#group_by" do
+
+    describe "on a really big list" do
+
+      before do
+        @list = Hamster.interval(0, STACK_OVERFLOW_DEPTH)
+      end
+
+      it "doesn't run out of stack" do
+        lambda { @list.group_by }.should_not raise_error
+      end
+
+    end
+
+    describe "with a block" do
+
+      [
+        [[], []],
+        [[1], [true => Hamster.list(1)]],
+        [[1, 2, 3, 4], [true => Hamster.list(3, 1), false => Hamster.list(4, 2)]],
+      ].each do |values, expected|
+
+        describe "on #{values.inspect}" do
+
+          before do
+            original = Hamster.list(*values)
+            @result = original.group_by(&:odd?)
+          end
+
+          it "returns #{expected.inspect}" do
+            @result.should == Hamster.hash(*expected)
+          end
+
+        end
+
+      end
+
+    end
+
+    describe "without a block" do
+
+      [
+        [[], []],
+        [[1], [1 => Hamster.list(1)]],
+        [[1, 2, 3, 4], [1 => Hamster.list(1), 2 => Hamster.list(2), 3 => Hamster.list(3), 4 => Hamster.list(4)]],
+      ].each do |values, expected|
+
+        describe "on #{values.inspect}" do
+
+          before do
+            original = Hamster.list(*values)
+            @result = original.group_by
+          end
+
+          it "returns #{expected.inspect}" do
+            @result.should == Hamster.hash(*expected)
+          end
+
+        end
+
+      end
+
+    end
+
+  end
+
+end

spec/hamster/set/one_spec.rb

@@ -0,0 +1,77 @@
+require File.expand_path(File.dirname(__FILE__) + '/../../spec_helper')
+
+require 'hamster/set'
+
+describe Hamster::Set do
+
+  describe "#one?" do
+
+    describe "when empty" do
+
+      before do
+        @set = Hamster.set
+      end
+
+      it "with a block returns false" do
+        pending do
+          @set.one? {}.should == false
+        end
+      end
+
+      it "with no block returns false" do
+        pending do
+          @set.one?.should == false
+        end
+      end
+
+    end
+
+    describe "when not empty" do
+
+      describe "with a block" do
+
+        before do
+          @set = Hamster.set("A", "B", "C")
+        end
+
+        it "returns false if the block returns true more than once" do
+          pending do
+            @set.one? { |item| true }.should == false
+          end
+        end
+
+        it "returns fale if the block never returns true" do
+          pending do
+            @set.one? { |item| false }.should == false
+          end
+        end
+
+        it "returns true if the block only returns true once" do
+          pending do
+            @set.one? { |item| item == "A" }.should == true
+          end
+        end
+
+      end
+
+      describe "with no block" do
+
+        it "returns false if more than one value is truthy" do
+          pending do
+            Hamster.set(nil, true, "A").one?.should == false
+          end
+        end
+
+        it "returns true if only one value is truthy" do
+          pending do
+            Hamster.set(nil, true, false).one?.should == true
+          end
+        end
+
+      end
+
+    end
+
+  end
+
+end