constraints-extras 0.2.3.0 → 0.2.3.1

raw patch · 2 files changed

+64/−1 lines, 2 filesPVP ok

version bump matches the API change (PVP)

API changes (from Hackage documentation)

Files

• README.md +62/−0
• constraints-extras.cabal +2/−1

@@ -0,0 +1,62 @@+# constraints-extras++## Example usage:++NB: This example can be built with `-pgmL markdown-unlit`.++```haskell+{-# LANGUAGE GADTs #-}+{-# LANGUAGE KindSignatures #-}+{-# LANGUAGE PolyKinds #-}+{-# LANGUAGE ScopedTypeVariables #-}+{-# LANGUAGE TemplateHaskell #-}+{-# LANGUAGE TypeApplications  #-}+{-# LANGUAGE TypeFamilies #-}+{-# LANGUAGE UndecidableInstances #-}+{-# LANGUAGE ExistentialQuantification #-}++import Data.Aeson+import Data.Constraint.Forall+import Data.Constraint.Extras+import Data.Constraint.Extras.TH++data A :: * -> * where+  A_a :: A Int+  A_b :: Int -> A ()++data B :: * -> * where+  B_a :: A a -> A a -> B a+  B_x :: Int -> B Int++data V :: (* -> *) -> * where+  V_a :: A Int -> V A++deriveArgDict ''A+deriveArgDict ''B+deriveArgDictV ''V++data DSum k f = forall a. DSum (k a) (f a)++-- Derive a ToJSON instance for our 'DSum'+instance forall k f.+  ( Has' ToJSON k f -- Given a value of type (k a), we can obtain an instance (ToJSON (f a))+  , ForallF ToJSON k -- For any (a), we have an instance (ToJSON (k a))+  ) => ToJSON (DSum k f) where+  toJSON (DSum (k :: k a) f) = toJSON+    ( whichever @ToJSON @k @a $ toJSON k -- Use the (ForallF ToJSON k) constraint to obtain the (ToJSON (k a)) instance+    , has' @ToJSON @f k $ toJSON f -- Use the (Has' ToJSON k f) constraint to obtain the (ToJSON (f a)) instance+    )++data Some k = forall a. Some (k a)++-- Derive a FromJSON instance for our 'DSum'+instance (FromJSON (Some f), Has' FromJSON f g) => FromJSON (DSum f g) where+  parseJSON x = do+    (jf, jg) <- parseJSON x+    Some (f :: f a) <- parseJSON jf+    g <- has' @FromJSON @g f (parseJSON jg)+    return $ DSum f g++main :: IO ()+main = return ()+```

@@ -1,5 +1,5 @@ name: constraints-extras-version: 0.2.3.0+version: 0.2.3.1 synopsis: Utility package for constraints description: Convenience functions and TH for working with constraints. See <https://github.com/obsidiansystems/constraints-extras/blob/develop/README.md README.md> for example usage. category: Constraints@@ -10,6 +10,7 @@ copyright: Obsidian Systems LLC build-type: Simple cabal-version: >=1.10+extra-source-files: README.md  library   exposed-modules: Data.Constraint.Extras, Data.Constraint.Extras.TH