Merge pull request #23 from haskell-servant/canonical-types

Add the `Canonicalize` type family to reduce API types to their canonical forms before proceeding in the other packages
This commit is contained in:
Alp Mestanogullari 2015-03-11 12:17:10 +01:00
commit 3311cbd901
3 changed files with 42 additions and 0 deletions

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@ -1,5 +1,6 @@
0.3
---
* Add a `Canonicalize` type family that distributes all `:>`s inside `:<|>`s to get to the canonical type of an API -- which is then used in all other packages to avoid weird handler types in *servant-server*.
* Multiple content-type/accept support for all the relevant combinators
* Provide *JSON*, *PlainText*, *OctetStream* and *FormUrlEncoded* content types out of the box
* Type-safe link generation to API endpoints

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@ -1,3 +1,6 @@
{-# LANGUAGE TypeFamilies #-}
{-# LANGUAGE TypeOperators #-}
{-# LANGUAGE UndecidableInstances #-}
module Servant.API (
-- * Combinators
@ -43,11 +46,16 @@ module Servant.API (
module Servant.Common.Text,
-- | Classes and instances for types that can be converted to and from @Text@
-- * Canonicalizing (flattening) API types
Canonicalize,
canonicalize,
-- * Utilities
module Servant.Utils.Links,
-- | Type-safe internal URIs
) where
import Data.Proxy (Proxy(..))
import Servant.Common.Text (FromText(..), ToText(..))
import Servant.API.Alternative ((:<|>) (..))
import Servant.API.Capture (Capture)
@ -69,3 +77,34 @@ import Servant.API.ReqBody (ReqBody)
import Servant.API.Sub ((:>))
import Servant.Utils.Links (HasLink (..), IsElem, IsElem',
URI (..), safeLink)
-- | Turn an API type into its canonical form.
--
-- The canonical form of an API type is basically the all-flattened form
-- of the original type. More formally, it takes a type as input and hands you
-- back an /equivalent/ type formed of toplevel `:<|>`-separated chains of `:>`s,
-- i.e with all `:>`s distributed inside the `:<|>`s.
--
-- It basically turns:
--
-- > "hello" :> (Get Hello :<|> ReqBody Hello :> Put Hello)
--
-- into
--
-- > ("hello" :> Get Hello) :<|> ("hello" :> ReqBody Hello :> Put Hello)
--
-- i.e distributing all ':>'-separated bits into the subsequent ':<|>'s.
type family Canonicalize api :: * where
-- requires UndecidableInstances
Canonicalize (a :> (b :<|> c)) = a :> Canonicalize b :<|> a :> Canonicalize c
Canonicalize ((a :<|> b) :> c) = a :> Canonicalize c :<|> b :> Canonicalize c
Canonicalize (a :> b) = Redex b (Canonicalize b) a
Canonicalize (a :<|> b) = Canonicalize a :<|> Canonicalize b
Canonicalize a = a
type family Redex a b c :: * where
Redex a a first = Canonicalize first :> a
Redex a b first = Canonicalize (first :> b)
canonicalize :: Proxy layout -> Proxy (Canonicalize layout)
canonicalize Proxy = Proxy

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@ -55,6 +55,8 @@ module Servant.API.ContentTypes
, AcceptHeader(..)
, AllCTRender(..)
, AllCTUnrender(..)
, AllMimeRender(..)
, AllMimeUnrender(..)
, FromFormUrlEncoded(..)
, ToFormUrlEncoded(..)
, IsNonEmpty