optional-args 1.0.0 → 1.0.1

raw patch · 2 files changed

+44/−21 lines, 2 files

Files

• optional-args.cabal +1/−1
• src/Data/Optional.hs +43/−20

@@ -1,5 +1,5 @@ Name: optional-args-Version: 1.0.0+Version: 1.0.1 Cabal-Version: >=1.10 Build-Type: Simple License: BSD3

@@ -3,78 +3,78 @@ {-# LANGUAGE DeriveTraversable #-}  -- | Use the `Optional` type for optional function arguments.  For example:--- +-- -- > import Data.Optional -- > -- > greet :: Optional String -> String -- > greet (Specific name) = "Hello, " ++ name -- > greet  Default        = "Hello"--- +-- -- >>> greet (Specific "John") -- "Hello, John" -- >>> greet Default -- "Hello"--- +-- --     The `Optional` type overloads as many Haskell literals as possible so --     that you do not need to wrap values in `Specific`.  For example, if you --     enable the `OverloadedStrings` extension you can use a naked string --     literal instead:--- +-- -- >>> :set -XOverloadedStrings -- >>> greet "John" -- "Hello, John"--- +-- --     The `Optional` type also implements `Num` and `Fractional`, so you can --     use numeric literals in place of `Optional` values:--- +-- -- > birthday :: Optional Int -> String -- > birthday (Specific age) = "You are " ++ show age ++ " years old!" -- > birthday  Default       = "You are one year older!"--- +-- -- >>> birthday 20 -- "You are 20 years old!" -- >>> birthday Default -- "You are one year older!"--- +-- --     The `IsString`, `Num`, and `Fractional` instances are recursive, so you --     can wrap your types in a more descriptive newtype and derive `IsString`, --     `Num` or `Fractional`:--- +-- -- > {-# LANGUAGE GeneralizedNewtypeDeriving #-}--- > +-- > -- > import Data.Optional -- > import Data.String (IsString)--- > +-- > -- > newtype Name = Name { getName :: String } deriving (IsString)--- > +-- > -- > greet :: Optional Name -> String -- > greet (Specific name) = "Hello, " ++ getName name -- > greet  Default        = "Hello"--- > +-- > -- > newtype Age = Age { getAge :: Int } deriving (Num)--- > +-- > -- > birthday :: Optional Age -> String -- > birthday (Specific age) = "You are " ++ show (getAge age) ++ " years old!" -- > birthday  Default       = "You are one year older!"--- +-- --     ... and you would still be able to provide naked numeric or string --     literals:--- +-- -- >>> :set -XOverloadedStrings -- >>> greet "John" -- "Hello, John" -- >>> birthday 20 -- "You are 20 years old!"--- +-- --     You can use `empty` as a short-hand for a `Default` argument:--- +-- -- >>> greet empty -- "Hello" -- >>> birthday empty -- "You are one year older!"--- +-- --     You can also use `pure` as a short-hand for a `Specific` argument:--- +-- -- >>> greet (pure "John") -- "Hello, John" -- >>> birthday (pure 20)@@ -83,6 +83,9 @@ module Data.Optional (     -- * Optional       Optional(..)+    , defaultTo+    , fromOptional+    , optional      -- * Re-exports     , empty@@ -147,3 +150,23 @@     recip = fmap recip      (/) = liftA2 (/)++-- | The 'optional' function takes a default value, a function, and an+-- 'Optional' value. If the 'Optional' value is 'Default', the function returns+-- the default value. Otherwise, it applies the function to the value inside the+-- 'Optional' and returns the result.+optional :: b -> (a -> b) -> Optional a -> b+optional n _ Default      = n+optional _ f (Specific x) = f x++-- | The 'defaultTo' function takes a default value and an 'Optional'+-- value.  If the 'Optional' is 'Default', it returns the default value;+-- otherwise, it returns the value contained in the 'Optional'.+defaultTo :: a -> Optional a -> a+defaultTo d Default      = d+defaultTo _ (Specific v) = v++-- | Convert an 'Optional' value into an instance of 'Alternative'.+fromOptional :: Alternative f => Optional a -> f a+fromOptional  Default     = empty+fromOptional (Specific x) = pure x