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LightAndLight/BindOf.hs

Last active July 24, 2017 01:19
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bindOf
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BindOf.hs
bindOf :: Monad m => Lens s t a b -> m s -> (a -> m b) -> m t
bindOf l ms f = do
s <- ms
b <- f (getConst $ l Const s)
pure $ s & l .~ b
@tonymorris
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bindOf :: forall s a m. Monad m => Lens s s a a -> m s -> (a -> m a) -> m s
bindOf l ms f = do
  s <- ms
  let typeof_s :: s
      typeof_s = s
  b <- f (s ^. l)
  let typeof_s_caret_dot_l :: a
      typeof_s_caret_dot_l = s ^. l
      typeof_f_s_caret_dot_l :: m a
      typeof_f_s_caret_dot_l = f (s ^. l)
      typeof_b :: a
      typeof_b = b
      typeof_l_dot_tilde_b :: s -> s
      typeof_l_dot_tilde_b = l .~ b
      typeof_s_amp_l_dot_tilde_b :: s
      typeof_s_amp_l_dot_tilde_b = s & l .~ b
  pure $ s & l .~ b

@tonymorris
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tonymorris commented Jul 24, 2017 •
edited 

bindOf :: forall s a. Lens s s a a -> ()
bindOf l =
  let y :: s -> a
      y = (^. l)
  in  ()

bindOW :: forall s a b. Lens s s a b -> ()
bindOW l =
  let y :: s -> b
      y = undefined -- (^. l)
  in  ()

@LightAndLight
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Author

Correct:

bindOf :: Monad m => Lens s t a b -> m s -> (a -> m b) -> m t
bindOf l ms f = do
  s <- ms
  b <- f (getConst $ l Const s)
  pure $ s & l .~ b

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