Implement #method_missing for each monad

lib/monads/monad.rb

@@ -6,6 +6,12 @@ def within(&block)
       end
     end
 
+    def method_missing(*args, &block)
+      within do |value|
+        value.public_send(*args, &block)
+      end
+    end
+
     private
 
     def ensure_monadic_result(&block)

spec/monads/eventually_spec.rb

@@ -88,5 +88,25 @@ module Monads
         end
       end
     end
+
+    describe 'handling unrecognised messages' do
+      let(:value) { double }
+      let(:response) { double }
+
+      before(:example) do
+        allow(value).to receive(:challenge).and_return(response)
+      end
+
+      it 'forwards any unrecognised message to the block’s value' do
+        expect(value).to receive(:challenge)
+        Eventually.new { |success| success.call(value) }.challenge.run {}
+      end
+
+      it 'returns the message’s result wrapped in an Eventually' do
+        @result = nil
+        Eventually.new { |success| success.call(value) }.challenge.run { |result| @result = result }
+        expect(@result).to eq response
+      end
+    end
   end
 end

spec/monads/many_spec.rb

@@ -69,5 +69,27 @@ module Monads
         end
       end
     end
+
+    describe 'handling unrecognised messages' do
+      let(:values) { [double, double, double] }
+      let(:responses) { [double, double, double] }
+
+      before(:example) do
+        values.zip(responses) do |value, response|
+          allow(value).to receive(:challenge).and_return(response)
+        end
+      end
+
+      it 'forwards any unrecognised message to each value' do
+        values.each do |value|
+          expect(value).to receive(:challenge)
+        end
+        many.challenge
+      end
+
+      it 'returns the messages’ results wrapped in a Many' do
+        expect(many.challenge.values).to eq responses
+      end
+    end
   end
 end

spec/monads/optional_spec.rb

@@ -76,5 +76,22 @@ module Monads
         end
       end
     end
+
+    describe 'handling unrecognised messages' do
+      let(:response) { double }
+
+      before(:example) do
+        allow(value).to receive(:challenge).and_return(response)
+      end
+
+      it 'forwards any unrecognised message to the value' do
+        expect(value).to receive(:challenge)
+        optional.challenge
+      end
+
+      it 'returns the message’s result wrapped in an Optional' do
+        expect(optional.challenge.value).to eq response
+      end
+    end
   end
 end