[Haskell-cafe] Parsec float

Jason Dusek jason.dusek at gmail.com
Sat May 30 14:12:56 EDT 2009

2009/05/30 Bartosz Wójcik <bartek at sudety.it>:
> ...reading RWH I could not memorize what those liftM funtions
> meant.

  The basic one, `liftM`, means `fmap`, though specialized for
  functors that are monads.

    Prelude Control.Monad> :t liftM
    liftM :: forall a b (m :: * -> *). (Monad m) => (a -> b) -> m a -> m b
    Prelude Control.Monad> :t fmap
    fmap :: forall a b (f :: * -> *). (Functor f) => (a -> b) -> f a -> f b

  I think we have `liftM` either to help the inferencer or due
  to the absence of a `(Functor m)` constraint in the definition
  of the `Monad` typeclass.

Jason Dusek

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