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eric-corumdigital/subscribeWithLast.purs

Created March 13, 2018 17:24
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purescript-behaviors subscribeWithLast
Raw
subscribeWithLast.purs
subscribeWithLast :: forall a b eff.
(b -> a -> Eff (frp :: FRP | eff) b)
-> b
-> Event a
-> Eff (frp :: FRP | eff) (Eff (frp :: FRP | eff) b)
subscribeWithLast f z evt = dropRefEff $ do
r <- newRef z
unsub <-
FRP.subscribe evt
(\e -> readRef r >>= \a -> addRefEff (f a e) >>= writeRef r)
pure (dropRefEff (unsub *> readRef r))
where
dropRefEff :: forall e x. Eff (ref :: REF | e) x -> Eff e x
dropRefEff = unsafeCoerceEff
addRefEff :: forall e x. Eff e x -> Eff (ref :: REF | e) x
addRefEff = unsafeCoerceEff
--
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