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MonadFail instance for GHC 8.6 #22

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MonadFail instance for GHC 8.6 #22

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8 changes: 8 additions & 0 deletions Graphics/PDF/Draw.hs
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Original file line number Diff line number Diff line change
Expand Up @@ -86,6 +86,9 @@ import Data.Maybe
#if !MIN_VERSION_base(4,8,0)
import Data.Monoid
#endif
#if MIN_VERSION_base(4,11,0)
import qualified Control.Monad.Fail as Fail
#endif

import qualified Data.Map.Strict as M
import qualified Data.IntMap as IM
Expand Down Expand Up @@ -186,6 +189,11 @@ instance Monad Draw where
unDraw (f a) env
return x = Draw $ \_env -> return x

#if MIN_VERSION_base(4,11,0)
instance Fail.MonadFail Draw where
fail s = Draw $ \_ -> Fail.fail s
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in my view this is the wrong way to go. the reason the original code was actually fine, was that the list is defined to be infinite, so that should be expressed by using, e.g., http://hackage.haskell.org/package/inflist-0.0.1/docs/src/Data-InfList.html#InfList

i've implemented that here: #27

#endif

instance MonadReader DrawEnvironment Draw where
ask = Draw $ \env -> return (drawEnvironment env)
local f m = Draw $ \env -> let drawenv' = f (drawEnvironment env)
Expand Down