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{-# LANGUAGE UndecidableInstances #-}
module Graphics.Glyph.ArrayGenerator where
import qualified Data.Map as M
import Data.Array
import Data.Maybe
data ArrayTransaction ix val b = ArrayBuilderM_ (M.Map ix val) b
instance (Ord ix) => Monad (ArrayTransaction ix a) where
return = ArrayBuilderM_ M.empty
(ArrayBuilderM_ map1 val) >>= f =
ArrayBuilderM_ (map1 `M.union` map2) val2
where (ArrayBuilderM_ map2 val2) = f val
class HasDefault a where
theDefault :: a
instance (Num a) => HasDefault a where
theDefault = 0
instance (HasDefault a, HasDefault b) => HasDefault (a,b) where
theDefault = (theDefault,theDefault)
instance (HasDefault a, HasDefault b, HasDefault c) => HasDefault (a,b,c) where
theDefault = (theDefault,theDefault,theDefault)
writeArray :: ix -> a -> ArrayTransaction ix a ()
writeArray index' val = ArrayBuilderM_ (M.singleton index' val) ()
buildArray :: (Ix ix) => (ix,ix) -> e -> ArrayTransaction ix e () -> Array ix e
buildArray bounds' def (ArrayBuilderM_ map' _) =
listArray bounds' [maybeLookup map' bound | bound <- range bounds']
where maybeLookup map_ key = fromMaybe def (M.lookup key map_)
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