53 lines
1.2 KiB
Elm
53 lines
1.2 KiB
Elm
module Lazy ( force, lazy, map, apply, bind
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) where
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{-| Library for efficient Lazy evaluation.
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# Delay
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@docs lazy
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# Evaluate
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@docs force
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# Transform
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@docs map, apply, bind
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-}
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import Basics ((<|), (.))
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import Native.Lazy
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data Lazy a = L { force : () -> a }
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{-| Delay a computation. This function memoizes results, so
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it guarantees that the computation will be evaluated at most once.
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-}
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lazy : (() -> a) -> Lazy a
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lazy t = L { force = (Native.Lazy.lazy t) }
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{-| Evaluate a lazy value. It saves the result so the second time
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you call `force` it does not run the computation again. -}
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force : Lazy a -> a
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force (L r) = r.force ()
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{-| Lazily apply a function to a lazy value. The computation
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will be delayed until you force the resulting value.
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-}
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map : (a -> b) -> Lazy a -> Lazy b
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map f t = lazy <| \() ->
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f . force <| t
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{-| Lazily apply a lazy function to a lazy value. This can
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be used to lazily apply a function to many arguments:
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```haskell
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f `map` a `apply` b `apply` c
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```
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-}
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apply : Lazy (a -> b) -> Lazy a -> Lazy b
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apply f x = lazy <| \() ->
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(force f) (force x)
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{-| Lazily chain together lazy computations. -}
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bind : Lazy a -> (a -> Lazy b) -> Lazy b
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bind x k = lazy <| \() ->
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force . k . force <| x
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