[Haskell-cafe] GHC Extension Proposal: ArgumentBlock

[Andreas Abel]

+1 to Andrew's original proposal.  It is as old as lambda-calculus 
itself, and I do not know why anything else was ever implemented for 
Haskell.

Agda got the parsing of \lambda right, and recently also the \forall.

 
https://github.com/agda/agda/commit/7d84d57aad07b4fd452a4a62c91a5b83fe7e6020

--Andreas

On 06.09.2015 00:55, Andrew Gibiansky wrote:
> 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  =  whenTrue  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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-- 
Andreas Abel  <><      Du bist der geliebte Mensch.

Department of Computer Science and Engineering
Chalmers and Gothenburg University, Sweden

andreas.abel at gu.se
http://www2.tcs.ifi.lmu.de/~abel/