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Why did I implement this overly complicated lift by hand again ?

This commit is contained in:
Tissevert 2020-02-07 13:08:10 +01:00
parent 95f9ab35b1
commit 03fbbc3a96
1 changed files with 3 additions and 7 deletions
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10
src/PDF/Pages.hs
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@ -8,7 +8,7 @@ module PDF.Pages (
import Codec.Compression.Zlib (decompress)
import Control.Applicative ((<|>))
import Control.Monad (foldM)
import Control.Monad.RWS (RWST(..), ask, evalRWST, mapRWST, modify)
import Control.Monad.RWS (RWST(..), ask, evalRWST, lift, modify)
import qualified Control.Monad.RWS as RWS (get)
import Data.ByteString (ByteString)
import qualified Data.ByteString.Lazy as Lazy (fromStrict, toStrict)
@ -35,15 +35,11 @@ data Page = Page {
infixl 1 \\=
(\\=) :: T a -> (a -> Either String b) -> T b
x \\= f = mapRWST ((\(a, s, w) -> (\b -> (b, s, w)) <$> f a) =<<) x
x \\= f = x >>= lift . f
infixl 1 //=
(//=) :: Either String a -> (a -> T b) -> T b
(//=) (Left e) _ = RWST (\_ _ -> Left e)
(//=) (Right a) f = f a
lift :: Either String a -> T a
lift x = x //= return
x //= f = lift x >>= f
expected :: Show a => String -> a -> Either String b
expected name = Left . printf "Not a %s: %s" name . show