Comments (2)
I don’t understand what swing does though – I can read the type and implementation, but I wouldn’t know a practical example of what it would be useful for. Löb has spreadsheets, what does swing have?
from articles.
I don't have a canonical example (yet). My intuition is that given some function (a -> b) -> f a -> _
swing will produce f (a -> b) -> a -> _
- that is, it somehow moves the f
.
Something I found really cool is what it does for fmap
:
fmap :: Functor f => (a -> b) -> f a -> f b
swing fmap :: Functor f => f (a -> b) -> a -> f b
(<*>) :: Applicative f => f (a -> b) -> f a -> f b
swing fmap = \fs a -> fs <*> pure a
So swing fmap
almost gives you a free Applicative
!
instance Applicative [] where
pure = swing fmap [id]
fs <*> [a] = swing fmap fs a
fs <*> as = undefined
-- Valid implementation of `ap` given Monoid:
instance Applicative [] where
fs <*> as = mconcat $ swing fmap fs <$> as
from articles.
Related Issues (20)
- reference to Data.Text.readMaybe, which does not exist
- Questionable claim in MFP2 HOT 4
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- `The second Functor law is redundant` is not proper HOT 3
- Remove warning from the second functor law article HOT 1
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- Invalid proof? HOT 3
- Small slip with $ HOT 4
- Inferred (rank 1) type of moeb could be more general HOT 1
- (a `op`) is \x -> a `op` x HOT 2
- State where not-bottom assumption was used HOT 3
- loeb: how to detect non-termination? HOT 1
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- zipWith question: flip in rotateUntil HOT 1
- zipWith question: Correctness of optimized Polygon Eq HOT 1
- Another approach to fix HOT 1
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from articles.