add mruby-enum-lazy mrbgem for Enumerable::Lazy

4 files changed, 206 insertions, 0 deletions

diff --git a/mrbgems/default.gembox b/mrbgems/default.gembox
index 2f436e5b6..1bba7be26 100644
--- a/mrbgems/default.gembox
+++ b/mrbgems/default.gembox
@@ -53,6 +53,9 @@ MRuby::GemBox.new do |conf|
   # Use Enumerator class (require mruby-fiber)
   conf.gem :core => "mruby-enumerator"
 
+  # Use Enumerable::Lazy class (require mruby-enumerator)
+  conf.gem :core => "mruby-enum-lazy"
+
   # Use extended toplevel object (main) methods
   conf.gem :core => "mruby-toplevel-ext"
 
diff --git a/mrbgems/mruby-enum-lazy/mrbgem.rake b/mrbgems/mruby-enum-lazy/mrbgem.rake
new file mode 100644
index 000000000..45dda4054
--- /dev/null
+++ b/mrbgems/mruby-enum-lazy/mrbgem.rake
@@ -0,0 +1,6 @@
+MRuby::Gem::Specification.new('mruby-enum-lazy') do |spec|
+  spec.license = 'MIT'
+  spec.author  = 'mruby developers'
+  spec.summary = 'Enumerable::Lazy class'
+  spec.add_dependency('mruby-enumerator')
+end
diff --git a/mrbgems/mruby-enum-lazy/mrblib/lazy.rb b/mrbgems/mruby-enum-lazy/mrblib/lazy.rb
new file mode 100644
index 000000000..088ce760d
--- /dev/null
+++ b/mrbgems/mruby-enum-lazy/mrblib/lazy.rb
@@ -0,0 +1,150 @@
+# = Enumerable#lazy implementation
+#
+# Enumerable#lazy returns an instance of Enumerable::Lazy.
+# You can use it just like as normal Enumerable object,
+# except these methods act as 'lazy':
+#
+#   - map       collect
+#   - select    find_all
+#   - reject
+#   - grep
+#   - drop
+#   - drop_while
+#   - take_while
+#   - flat_map  collect_concat
+#   - zip
+#
+# == Acknowledgements
+#
+#   Based on https://github.com/yhara/enumerable-lazy
+#   Inspired by https://github.com/antimon2/enumerable_lz
+#   http://jp.rubyist.net/magazine/?0034-Enumerable_lz (ja)
+
+module Enumerable
+  def lazy
+    Lazy.new(self)
+  end
+
+  class Lazy < Enumerator
+    def initialize(obj, &block)
+      super(){|yielder|
+        begin
+          obj.each{|x|
+            if block
+              block.call(yielder, x)
+            else
+              yielder << x
+            end
+          }
+        rescue StopIteration
+        end
+      }
+    end
+
+    def map(&block)
+      Lazy.new(self){|yielder, val|
+        yielder << block.call(val)
+      }
+    end
+    alias collect map
+
+    def select(&block)
+      Lazy.new(self){|yielder, val|
+        if block.call(val)
+          yielder << val
+        end
+      }
+    end
+    alias find_all select
+
+    def reject(&block)
+      Lazy.new(self){|yielder, val|
+        if not block.call(val)
+          yielder << val
+        end
+      }
+    end
+
+    def grep(pattern)
+      Lazy.new(self){|yielder, val|
+        if pattern === val
+          yielder << val
+        end
+      }
+    end
+
+    def drop(n)
+      dropped = 0
+      Lazy.new(self){|yielder, val|
+        if dropped < n
+          dropped += 1
+        else
+          yielder << val
+        end
+      }
+    end
+
+    def drop_while(&block)
+      dropping = true
+      Lazy.new(self){|yielder, val|
+        if dropping
+          if not block.call(val)
+            yielder << val
+            dropping = false
+          end
+        else
+          yielder << val
+        end
+      }
+    end
+    
+    def take(n)
+      if n == 0
+        return Lazy.new(self){raise StopIteration}
+      end
+      taken = 0
+      Lazy.new(self){|yielder, val|
+        yielder << val
+        taken += 1
+        if taken >= n
+          raise StopIteration
+        end
+      }
+    end
+
+    def take_while(&block)
+      Lazy.new(self){|yielder, val|
+        if block.call(val)
+          yielder << val
+        else
+          raise StopIteration
+        end
+      }
+    end
+
+    def flat_map(&block)
+      Lazy.new(self){|yielder, val|
+        ary = block.call(val)
+        # TODO: check ary is an Array
+        ary.each{|x|
+          yielder << x
+        }
+      }
+    end
+    alias collect_concat flat_map
+
+    def zip(*args, &block)
+      enums = [self] + args
+      Lazy.new(self){|yielder, val|
+        ary = enums.map{|e| e.next}
+        if block
+          yielder << block.call(ary)
+        else
+          yielder << ary
+        end
+      }
+    end
+
+    alias force to_a
+  end
+end
diff --git a/mrbgems/mruby-enum-lazy/test/lazy.rb b/mrbgems/mruby-enum-lazy/test/lazy.rb
new file mode 100644
index 000000000..ca009d34c
--- /dev/null
+++ b/mrbgems/mruby-enum-lazy/test/lazy.rb
@@ -0,0 +1,47 @@
+assert("Enumerable::Lazy") do
+  a = [1, 2]
+  assert_equal Enumerable::Lazy, a.lazy.class
+end
+
+assert("Enumerable::Lazy laziness") do
+  a = Object.new
+  def a.each
+    return to_enum :each unless block_given?
+    self.b << 10
+    yield 1
+    self.b << 20
+    yield 2
+    self.b << 30
+    yield 3
+    self.b << 40
+    yield 4
+    self.b << 50
+    yield 5
+  end
+  def a.b(b=nil)
+    @b = b if b
+    @b
+  end
+
+  a.b([])
+  assert_equal [1,2], a.each.lazy.take(2).force
+  assert_equal [10,20], a.b
+
+  a.b([])
+  assert_equal [2,4], a.each.lazy.select{|x|x%2==0}.take(2).force
+  assert_equal [10,20,30,40], a.b
+
+  a.b([])
+  assert_equal [1], a.each.lazy.take_while{|x|x<2}.take(1).force
+  assert_equal [10], a.b
+
+  a.b([])
+  assert_equal [1], a.each.lazy.take_while{|x|x<2}.take(4).force
+  assert_equal [10,20], a.b
+end
+
+assert("Enumerable::Lazy#zip with cycle") do
+  e1 = [1, 2, 3].cycle
+  e2 = [:a, :b].cycle
+  assert_equal [[1,:a],[2,:b],[3,:a]], e1.lazy.zip(e2).first(3)
+end