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Lenses are not always better: (kbin.social)

submitted 2 years ago* (last edited 2 years ago) by jaror@kbin.social to c/haskell@kbin.social

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Lenses are not always better:

fresh :: FDState s c -> (Int, FDState s c)
fresh = id &&& id
  >>> first (^. nextId)
  >>> (\(i, s) -> (i, s & alive %~ Set.insert i))
  >>> second (nextId %~ (+ 1))

fresh :: FDState s c -> (Int, FDState s c)
fresh s@FDState {_nextId = i, _alive = as} =
  (i, s {_nextId = i + 1, _alive = Set.insert i as})

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[–] bitcrafter 1 points 2 years ago* (last edited 2 years ago)

That's not really an argument against lenses so much as an argument against extreme point-free style.

fresh :: FDState s c -> (Int, FDState s c)
fresh s = (i, inc_s &amp; alive %~ Set.insert i)
  where (i, inc_s) = s &amp; nextID &lt;&lt;+~ 1

Edit: Fixed some of the operators being replaced with HTML entities. Edit 2: Hmm, they keep showing up fine in Preview but then getting replaced again. I'm not sure what I'm supposed to do to make them work.