monads.rb in dry-monads-0.4.0

- old
+ new
@@ -1,43 +1,66 @@
-require 'dry/monads/either'
+require 'dry/core/constants'
 require 'dry/monads/maybe'
 require 'dry/monads/try'
 require 'dry/monads/list'
+require 'dry/monads/result'
+require 'dry/monads/result/fixed'
 
 module Dry
   # @api public
   module Monads
-    extend self
+    Undefined = Dry::Core::Constants::Undefined
 
-    # Stores the given value in one of the subtypes of {Maybe} monad.
-    # It is essentially a wrapper for {Maybe.lift}.
-    #
-    # @param value [Object] the value to be stored in the monad
-    # @return [Maybe::Some, Maybe::None]
-    def Maybe(value)
-      Maybe.lift(value)
-    end
+    CONSTRUCTORS = [
+      Maybe::Mixin::Constructors,
+      Result::Mixin::Constructors
+    ].freeze
 
-    # @param value [Object] the value to be stored in the monad
-    # @return [Maybe::Some]
-    def Some(value)
-      Maybe::Some.new(value)
-    end
+    Some = Maybe::Some
+    None = Maybe::None
+    Success = Result::Success
+    Failure = Result::Failure
 
-    # @return [Maybe::None]
-    def None
-      Maybe::Some::None.instance
-    end
+    extend(*CONSTRUCTORS)
 
-    # @param value [Object] the value to be stored in the monad
-    # @return [Either::Right]
-    def Right(value)
-      Either::Right.new(value)
+    def self.included(base)
+      super
+
+      base.include(*CONSTRUCTORS)
     end
 
-    # @param value [Object] the value to be stored in the monad
-    # @return [Either::Left]
-    def Left(value)
-      Either::Left.new(value)
+    # Creates a module that has two methods: `Success` and `Failure`.
+    # `Success` is identical to {Result::Mixin::Constructors#Success} and Failure
+    # rejects values that don't conform the value of the `error`
+    # parameter. This is essentially a Result type with the `Failure` part
+    # fixed.
+    #
+    # @example using dry-types
+    #   module Types
+    #     include Dry::Types.module
+    #   end
+    #
+    #   class Operation
+    #     # :user_not_found and :account_not_found are the only
+    #     # values allowed as failure results
+    #     Error =
+    #       Types.Value(:user_not_found) |
+    #       Types.Value(:account_not_found)
+    #
+    #     def find_account(id)
+    #       account = acount_repo.find(id)
+    #
+    #       account ? Success(account) : Failure(:account_not_found)
+    #     end
+    #
+    #     def find_user(id)
+    #       # ...
+    #     end
+    #   end
+    #
+    # @param error [#===] the type of allowed failures
+    # @return [Module]
+    def self.Result(error, **options)
+      Result::Fixed[error, **options]
     end
   end
 end