Re: Pattern synonyms and record fields for Cont, Writer, Reader, State, ...

This [1] was posted 5 hours ago [1] https://www.reddit.com/r/haskellquestions/comments/5ebepq/perhaps_i_meant_on... 2016-11-20 17:56 GMT+00:00 David Feuer :

This sounds fantastic! I think it is very important to provide sufficient documentation in the source to allow newish users who click through to understand as much as they need.

On Nov 20, 2016 12:47 PM, "Baldur Blöndal" wrote:

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This will look like the original definitions [1]

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newtype State s a = State { runState :: s -> (a, s) }

before they became type synonyms

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type State s = StateT s Identity

by defining pattern synonyms

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pattern State :: (s -> (a, s)) -> State s a pattern State {runState} <- S.runState -> runState where State a = state a

Trac ticket #12767 for further information. [2]

[1] http://book.realworldhaskell.org/read/monads.html#id643643 [2] https://ghc.haskell.org/trac/ghc/ticket/12767

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