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tail call recursive implementation of BacktrackM

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kr.angelov
2006-06-21 19:17:25 +00:00
parent 057c5132ed
commit fb8ea2c2f4
1 changed files with 3 additions and 2 deletions
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5
src/GF/Data/BacktrackM.hs
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@@ -29,6 +29,7 @@ module GF.Data.BacktrackM ( -- * the backtracking state monad
foldFinalStates, finalStates
) where
import Data.List
import Control.Monad
----------------------------------------------------------------------
@@ -80,7 +81,7 @@ failure :: BacktrackM s a
failure = BM (\c s b -> b)
(|||) :: BacktrackM s a -> BacktrackM s a -> BacktrackM s a
(BM f) ||| (BM g) = BM (\c s b -> f c s (g c s b))
(BM f) ||| (BM g) = BM (\c s b -> g c s $! f c s b)
instance MonadPlus (BacktrackM s) where
mzero = failure
@@ -89,4 +90,4 @@ instance MonadPlus (BacktrackM s) where
-- * specific functions on the backtracking monad
member :: [a] -> BacktrackM s a
member = msum . map return
member xs = BM (\c s b -> foldl' (\b x -> c x s b) b xs)