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Add a function to update cons records.

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This commit is contained in:
Rob Rix 2016-07-21 18:53:56 -04:00
parent 590509aaf8
commit 318d001512
1 changed files with 6 additions and 1 deletions
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7
src/Data/Record.hs
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@ -1,4 +1,4 @@
{-# LANGUAGE DataKinds, GADTs, KindSignatures, MultiParamTypeClasses, TypeOperators #-}
{-# LANGUAGE DataKinds, GADTs, KindSignatures, MultiParamTypeClasses, ScopedTypeVariables, TypeOperators #-}
module Data.Record where
import GHC.Show
@ -23,6 +23,11 @@ maybeGetField :: Typeable field => Record fields -> Maybe field
maybeGetField (RCons h t) = cast h <|> maybeGetField t
maybeGetField RNil = Nothing
updateRCons :: forall h t field. (Typeable h, Typeable field) => Record (h ': t) -> field -> Record (h ': t)
updateRCons (RCons h t) a = case eqT :: Maybe (h :~: field) of
Just Refl -> RCons a t
Nothing -> RCons h (updateField t a)
-- Classes