Merge pull request #464 from opal/promise

Implement promises
opal · Dec 25, 2013 · 9b67f08 · 9b67f08
2 parents abb78c1 + 86a79c9
commit 9b67f08
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diff --git a/spec/opal/stdlib/promise/collect_spec.rb b/spec/opal/stdlib/promise/collect_spec.rb
@@ -0,0 +1,35 @@
+require 'promise'
+
+describe 'Promise#collect' do
+  it 'calls the block with all the previous results' do
+    x = 42
+
+    Promise.value(1).then { 2 }.then { 3 }.collect {|a, b, c|
+      x = a + b + c
+    }
+
+    x.should == 6
+  end
+
+  it 'calls the then after the collect' do
+    x = 42
+
+    Promise.value(1).then { 2 }.then { 3 }.collect {|a, b, c|
+      a + b + c
+    }.then { |v| x = v }
+
+    x.should == 6
+  end
+
+  it 'works after a when' do
+    x = 42
+
+    Promise.value(1).then {
+      Promise.when Promise.value(2), Promise.value(3)
+    }.collect {|a, b|
+      x = a + b[0] + b[1]
+    }
+
+    x.should == 6
+  end
+end
diff --git a/spec/opal/stdlib/promise/error_spec.rb b/spec/opal/stdlib/promise/error_spec.rb
@@ -0,0 +1,15 @@
+require 'promise'
+
+describe 'Promise.error' do
+  it 'rejects the promise with the given error' do
+    Promise.error(23).error.should == 23
+  end
+
+  it 'marks the promise as realized' do
+    Promise.error(23).realized?.should be_true
+  end
+
+  it 'marks the promise as rejected' do
+    Promise.error(23).rejected?.should be_true
+  end
+end
diff --git a/spec/opal/stdlib/promise/rescue_spec.rb b/spec/opal/stdlib/promise/rescue_spec.rb
@@ -0,0 +1,35 @@
+require 'promise'
+
+describe 'Promise#rescue' do
+  it 'calls the block when the promise has already been rejected' do
+    x = 42
+    Promise.error(23).rescue { |v| x = v }
+    x.should == 23
+  end
+
+  it 'calls the block when the promise is rejected' do
+    a = Promise.new
+    x = 42
+
+    a.rescue { |v| x = v }
+    a.reject(23)
+
+    x.should == 23
+  end
+
+  it 'does not call then blocks when the promise is rejected' do
+    x = 42
+    y = 23
+
+    Promise.error(23).then { y = 42 }.rescue { |v| x = v }
+
+    x.should == 23
+    y.should == 23
+  end
+
+  it 'does not call subsequent rescue blocks' do
+    x = 42
+    Promise.error(23).rescue { |v| x = v }.rescue { x = 42 }
+    x.should == 23
+  end
+end
diff --git a/spec/opal/stdlib/promise/then_spec.rb b/spec/opal/stdlib/promise/then_spec.rb
@@ -0,0 +1,38 @@
+require 'promise'
+
+describe 'Promise#then' do
+  it 'calls the block when the promise has already been resolved' do
+    x = 42
+    Promise.value(23).then { |v| x = v }
+    x.should == 23
+  end
+
+  it 'calls the block when the promise is resolved' do
+    a = Promise.new
+    x = 42
+
+    a.then { |v| x = v }
+    a.resolve(23)
+
+    x.should == 23
+  end
+
+  it 'works with multiple chains' do
+    x = 42
+    Promise.value(2).then { |v| v * 2 }.then { |v| v * 4 }.then { |v| x = v }
+    x.should == 16
+  end
+
+  it 'works when a block returns a promise' do
+    a = Promise.new
+    b = Promise.new
+
+    x = 42
+    a.then { b }.then { |v| x = v }
+
+    a.resolve(42)
+    b.resolve(23)
+
+    x.should == 23
+  end
+end
diff --git a/spec/opal/stdlib/promise/value_spec.rb b/spec/opal/stdlib/promise/value_spec.rb
@@ -0,0 +1,15 @@
+require 'promise'
+
+describe 'Promise.value' do
+  it 'resolves the promise with the given value' do
+    Promise.value(23).value.should == 23
+  end
+
+  it 'marks the promise as realized' do
+    Promise.value(23).realized?.should be_true
+  end
+
+  it 'marks the promise as resolved' do
+    Promise.value(23).resolved?.should be_true
+  end
+end
diff --git a/spec/opal/stdlib/promise/when_spec.rb b/spec/opal/stdlib/promise/when_spec.rb
@@ -0,0 +1,19 @@
+require 'promise'
+
+describe 'Promise.when' do
+  it 'calls the block with all promises results' do
+    a = Promise.new
+    b = Promise.new
+
+    x = 42
+
+    Promise.when(a, b).then {|y, z|
+      x = y + z
+    }
+
+    a.resolve(1)
+    b.resolve(2)
+
+    x.should == 3
+  end
+end
diff --git a/stdlib/promise.rb b/stdlib/promise.rb
@@ -0,0 +1,235 @@
+class Promise
+  def self.value(value)
+    new.resolve(value)
+  end
+
+  def self.error(value)
+    new.reject(value)
+  end
+
+  def self.when(*promises)
+    When.new(promises.flatten)
+  end
+
+  attr_reader :value, :error, :prev, :next
+
+  def initialize(success = nil, failure = nil)
+    @success = success
+    @failure = failure
+
+    @realized = nil
+    @value    = nil
+    @error    = nil
+    @delayed  = nil
+
+    @prev = nil
+    @next = nil
+  end
+
+  def act?
+    @success != nil
+  end
+
+  def realized?
+    @realized != nil
+  end
+
+  def resolved?
+    @realized == :value
+  end
+
+  def rejected?
+    @realized == :error
+  end
+
+  def ^(promise)
+    promise << self
+    self    >> promise
+
+    promise
+  end
+
+  def <<(promise)
+    @prev = promise
+
+    self
+  end
+
+  def >>(promise)
+    @next = promise
+
+    if resolved?
+      promise.resolve(@delayed || value)
+    elsif rejected? && (!@failure || Promise === (@delayed || @error))
+      promise.reject(@delayed || error)
+    end
+
+    self
+  end
+
+  def resolve(value)
+    if realized?
+      raise ArgumentError, 'the promise has already been realized'
+    end
+
+    if Promise === value
+      value << @prev
+
+      return value ^ self
+    end
+
+    @realized = :value
+    @value    = value
+
+    if @success
+      value = @success.call(value)
+    end
+
+    if @next
+      @next.resolve(value)
+    else
+      @delayed = value
+    end
+
+    self
+  end
+
+  def reject(value)
+    if realized?
+      raise ArgumentError, 'the promise has already been realized'
+    end
+
+    if Promise === value
+      value << @prev
+
+      return value ^ self
+    end
+
+    @realized = :error
+    @error    = value
+
+    if @failure
+      value = @failure.call(value)
+
+      if Promise === value
+        if @next
+          @next.reject(value)
+        else
+          @delayed = value
+        end
+      end
+    else
+      if @next
+        @next.reject(value)
+      else
+        @delayed = value
+      end
+    end
+
+    self
+  end
+
+  def then(&block)
+    self ^ Promise.new(block)
+  end
+
+  alias do then
+
+  def fail(&block)
+    self ^ Promise.new(nil, block)
+  end
+
+  alias rescue fail
+  alias catch fail
+
+  def always(&block)
+    self ^ Promise.new(block, block)
+  end
+
+  alias finally always
+  alias ensure always
+
+  def collect(&block)
+    self ^ Collect.new(block)
+  end
+
+  def inspect
+    result = "#<#{self.class}(#{object_id})"
+
+    if @next
+      result += " >> #{@next.inspect}"
+    end
+
+    if realized?
+      result += ": #{(@value || @error).inspect}>"
+    else
+      result += ">"
+    end
+
+    result
+  end
+
+  class Collect < self
+    def self.it(promise)
+      unless promise.realized?
+        raise ArgumentError, "the promise hasn't been realized"
+      end
+
+      current = promise.act? ? [promise.value] : []
+
+      if prev = promise.prev
+        current.concat(it(prev))
+      else
+        current
+      end
+    end
+
+    def initialize(block)
+      super -> {
+        block.call(*Collect.it(self).reverse)
+      }
+    end
+  end
+
+  class When < self
+    def initialize(promises = [])
+      super()
+
+      @wait = []
+
+      promises.each {|promise|
+        wait promise
+      }
+    end
+
+    def wait(promise)
+      @wait << promise
+
+      promise.always {
+        try if @next
+      }
+
+      self
+    end
+
+    def >>(*)
+      super.tap {
+        try
+      }
+    end
+
+    def try
+      if @wait.all?(&:realized?)
+        if promise = @wait.find(&:rejected?)
+          reject(promise.error)
+        else
+          resolve(@wait.map(&:value))
+        end
+      end
+    end
+
+    def and(&block)
+      wait Promise.new(block)
+    end
+  end
+end