Add joining functions #131
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joshgodsiff
commented
Feb 8, 2019
| @@ -1 +1 @@ | |||
| resolver: lts-7.14 | |||
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The project was no-longer buildable under this, so I updated it to a fairly recent one.
joshgodsiff
commented
Feb 8, 2019
| {-| Join two 'Fold's by applying joining functions to their inputs and | ||
| outputs. | ||
| -} | ||
| joinWith :: (e -> a) -> (e -> c) -> (b -> d -> f) -> Fold a b -> Fold c d -> Fold e f |
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Example: joinWith fst snd (,) will give you a Fold a b -> Fold c d -> Fold (a,c) (b,d)
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I don't think these joining functions are necessary because they can be implemented in terms of existing type class methods concisely. For example: joinOutputsWith = liftA2
joinWith inL inR out foldL foldR = liftA2 out (lmap inL foldL) (lmap inR foldR)I think there is something still worth adding, which is a utility of the following type: postMapM :: (a -> m b) -> FoldM m i a -> FoldM m i b... because then that would dmake joinOutputsWithM f foldL foldR = postMapM id (liftA2 f foldL foldR)
joinWIthM inL inR out = postMapM id (liftA2 f (lmap inL foldL) (lmap inR folddR)) |
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