Merge pull request #29 from alex-lairan/add_or_block

Add or block

spec/monads/maybe/just_spec.cr

@@ -47,6 +47,12 @@ describe Monads::Just do
       exclude = Monads::Just.new(3)
       monad.or(exclude).should eq(monad)
     end
+
+    it "result himself with lambda" do
+      monad = Monads::Just.new(1)
+      exclude = Monads::Just.new(3)
+      monad.or(-> { exclude }).should eq(monad)
+    end
   end
 
   describe "#bind" do

spec/monads/maybe/nothing_spec.cr

@@ -35,11 +35,17 @@ describe Monads::Nothing do
   end
 
   describe "#or" do
-    it "result himself" do
+    it "result exclude" do
       monad = Monads::Nothing(String).new
       exclude = Monads::Just.new("Foo")
       monad.or(exclude).should eq(exclude)
     end
+
+    it "result exclude result" do
+      monad = Monads::Nothing(Int32).new
+      exclude = Monads::Just.new(3)
+      monad.or(-> { exclude }).should eq(exclude)
+    end
   end
 
   describe "#bind" do

src/monads/maybe.cr

@@ -64,6 +64,10 @@ module Monads
       Just.new(value!)
     end
 
+    def or(lambda : -> _) : Maybe(T)
+      Just.new(value!)
+    end
+
     def map_or(default : U, lambda : T -> U) forall U
       lambda.call(value!)
     end
@@ -99,6 +103,10 @@ module Monads
       default
     end
 
+    def or(lambda : -> _)
+      lambda.call
+    end
+
     def map_or(default : U, lambda : _ -> _) forall U
       default
     end