[Haskell-cafe] GHC Extension Proposal: ArgumentBlock

[Fumiaki Kinoshita]

It would be quite useful. It allows us to write

    foo $!%$*~ runBarT do ...

Instead of

    (foo $!%$*~) $ runBarT $ do ...

2015-09-06 7:55 GMT+09:00 Andrew Gibiansky <andrew.gibiansky at gmail.com>:

> I'd like to propose a GHC extension called (for now) `ArgumentBody`.
> `ArgumentBody` is a simple syntax extension, than, when enabled, permits
> the following code:
>
> main = when True do
>   putStrLn "Hello!"
>
>
> main = forM values \value ->
>   print value
>
>
> main = forM values \case
>     Just x -> print x
>     Nothing -> print y
>
>
> In this code we do not need `$` before `do`, lambda, or lambda-case (if
> -XLambdaCase is enabled). This change would *not* extend to `let`, `if`,
> `case`, or any other constructs.
>
> Pros:
>
> 1. Code is simpler and it greatly reduces the need for "operator line
> noise" of $ everywhere.
> 2. We can avoid using the type-checker hack for $
> <http://stackoverflow.com/questions/9468963/runst-and-function-composition>
> for things such as runSt.
>
> Cons:
>
> 1. Adds complexity to the compiler. (NB: The change is minimal and not
> invasive at all.)
> 2. Contributes to a proliferation of extensions that other tools must
> support.  (NB: This is just a parser change so should be easy for all tools
> to support.)
>
> I'm very interested in hearing both favoring and dissenting opinions on
> this proposed change. If this change is approved of, names besides
> -XArgumentBody can be considered.
>
> See more info on Trac
> <https://ghc.haskell.org/trac/ghc/ticket/10843#ticket>.
>
> -- Andrew Gibiansky
>
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