jaror, 10 months ago

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})

#haskell