[ghc-steering-committee] Proposal: BlockArguments (Shepherd: Joachim)

[Joachim Breitner]

Dear committee,

the BlockArguments (former ArgumentDo) proposal was brought before us:
https://github.com/ghc-proposals/ghc-proposals/pull/90

I’ll shepherd this myself.

The idea is to not require parenthesis around block syntax elements
such as lambda expressions, let bindings, if-then-else, case-of and (in
particular) do expressions. The change to the grammar to enable that is
actually a simplificiation (it removes one non-terminal, lexp).

Variants proposed are:
 * do this only for `do` in argument position, or
 * do it for all blocks, but only in function argument positions.


I am fond of this proposal, because it allows code with less
parenthesis to be written. If Haskell was written from ground up, I
believe there would be little opposition to this setup, and maybe we
would not have had to hack higher-rank support into ($), as the idiom 
`runST $ do …` would just be `runST do …`.

Another argument in favor of it is the mentioned simplificiation of the
grammar rules.

I am aware that reading the parenthesis-free code feels strange to
many, but I not overly worried about that: Every change feels strange,
and in this case, only code that is otherwise illegal is affected.

Akio has indicated that he is willing to work on the implementation.


Therefore, I suggest that we accept this proposal.


Please discuss (or voice you silent agreement).

Regards,
Joachim

-- 
Joachim Breitner
  mail at joachim-breitner.de
  http://www.joachim-breitner.de/
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