reflection 1.5.1.1 → 1.5.1.2

raw patch · 4 files changed

+79/−5 lines, 4 filesPVP ok

version bump matches the API change (PVP)

API changes (from Hackage documentation)

Files

• CHANGELOG.markdown +4/−0
• examples/FromJSON.hs +70/−0
• fast/Data/Reflection.hs +3/−4
• reflection.cabal +2/−1

@@ -1,3 +1,7 @@+# 1.5.1.2+* Builds warning-free on GHC 7.10.+* Added a dynamic FromJSON example.+ # 1.5.1.1 * Updated the link to the paper. * More examples.

@@ -0,0 +1,70 @@+-- Example of a dynamically generated FromJSON instance.+--+-- Can be useful when one needs to use a function with a +-- FromJSON constraint, but some detail about the +-- conversion from JSON is not known until runtime.+{-# LANGUAGE Rank2Types #-}+{-# LANGUAGE FlexibleContexts #-}+{-# LANGUAGE UndecidableInstances #-}+{-# LANGUAGE ScopedTypeVariables #-}+{-# LANGUAGE OverloadedStrings #-}++import Data.Reflection -- from reflection+import Data.Monoid     -- from base+import Data.Proxy      -- from tagged+import Data.Text       -- from text+import Data.Monoid  +import Data.Aeson      -- from aeson     +import Data.Aeson.Types (Parser)++import Control.Applicative++-- These imports are only for constructing the example value+import Control.Lens (preview)           -- from lens+import Data.Aeson.Lens (_Value,_String) -- form lens-aeson++data Foo = Foo+    {+        field1 :: Int+    ,   field2 :: Int+    } deriving (Show)++fooParser :: Text -> Object -> Parser Foo+fooParser prefix o = do+    Foo <$> o .: (prefix <> "field1") <*> o .: (prefix <> "field2")++-- A wrapper over Foo carrying a phantom type s+newtype J a s = J { runJ :: a }+ +-- If the phantom type s reifies the parsing function, we can +-- use reflect to recover the function and implement +-- our FromJSON instance for J.+instance Reifies s (Object -> Parser a) => FromJSON (J a s) where+    parseJSON (Object v) = J <$> reflect (Proxy :: Proxy s) v+ +-- Convince the compiler that the phantom type in the proxy+-- supplied by reify is the same as the phantom type in J. +--+-- Otherwise the FromJSON instance for J won't kick in.+asProxyJ :: Proxy s -> J a s -> J a s+asProxyJ _ = id++exampleJSON :: Value+exampleJSON = maybe Null id (preview _Value str)+  where+    str = "{ \"zzfield1\" : 5, \"zzfield2\" : 7 }"::Text+ +main :: IO ()+main = do+    putStrLn "Enter prefix for the fields: "+    -- "zz" must be entered for the parse to succeed+    prefix <- fmap pack getLine+ +    -- fromJSON uses the dynamically generated FromJSON instance+    let result = reify (fooParser prefix) $ \proxy ->+            -- We must eliminate the J newtype before returning+            -- because, thanks to parametricity,+            -- the phantom type cannot escape the callback.+            runJ . asProxyJ proxy <$> fromJSON exampleJSON + +    putStrLn (show (result :: Result Foo))

@@ -69,7 +69,6 @@     , Z, D, SD, PD     ) where -import Data.Functor import Data.Proxy  #if (defined(__GLASGOW_HASKELL__) && __GLASGOW_HASKELL__ >= 707) || (TEMPLATE_HASKELL && USE_TYPE_LITS)@@ -155,15 +154,15 @@ {-# INLINE retagPD #-}  instance Reifies n Int => Reifies (D n) Int where-  reflect = (\n -> n + n) <$> retagD reflect+  reflect = (\n -> n + n) `fmap` retagD reflect   {-# INLINE reflect #-}  instance Reifies n Int => Reifies (SD n) Int where-  reflect = (\n -> n + n + 1) <$> retagSD reflect+  reflect = (\n -> n + n + 1) `fmap` retagSD reflect   {-# INLINE reflect #-}  instance Reifies n Int => Reifies (PD n) Int where-  reflect = (\n -> n + n - 1) <$> retagPD reflect+  reflect = (\n -> n + n - 1) `fmap` retagPD reflect   {-# INLINE reflect #-}  #ifdef TEMPLATE_HASKELL

@@ -1,5 +1,5 @@ name:           reflection-version:        1.5.1.1+version:        1.5.1.2 license:        BSD3 license-file:   LICENSE author:         Edward A. Kmett, Elliott Hird, Oleg Kiselyov and Chung-chieh Shan@@ -71,6 +71,7 @@  extra-source-files:   examples/Monoid.hs+  examples/FromJSON.hs   examples/Constraints.hs   examples/Benchmark.hs   CHANGELOG.markdown