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20 lines
528 B
Idris
20 lines
528 B
Idris
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module LazyFoldlM
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import Data.List.Lazy
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import Debug.Trace
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foldlM' : Monad m => (fm : b -> a -> m b) -> (init : b) -> LazyList a -> m b
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foldlM' fm init xs = foldrLazy (\x, k, z => fm z x >>= k) pure xs init
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l : LazyList Nat
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l = (\n => trace "gen \{show n}" n) <$> iterateN 10000 (+1) 0
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-- Both should be actually short-cutting (i.e., not many `gen *` should be printed)
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x : Maybe Nat
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x = foldlM' (\m, n => if m <= 1 then Just n else Nothing) 0 l
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y : Maybe Nat
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y = foldlM (\m, n => if m <= 1 then Just n else Nothing) 0 l
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