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

[Simon Peyton Jones]

I'm neutral on this.  Clearly it's purely a UI issue; there is little impact on the compiler.

I'm a bit bothered not so much by knowing were one of these block-arguments /begin/ as knowing where it /ends/.  But I'm not opposing.

Simon

| -----Original Message-----
| From: ghc-steering-committee [mailto:ghc-steering-committee-
| bounces at haskell.org] On Behalf Of Joachim Breitner
| Sent: 27 November 2017 14:47
| To: ghc-steering-committee at haskell.org
| Subject: [ghc-steering-committee] Proposal: BlockArguments (Shepherd:
| Joachim)
| 
| Dear committee,
| 
| the BlockArguments (former ArgumentDo) proposal was brought before us:
| https://na01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.c
| om%2Fghc-proposals%2Fghc-
| proposals%2Fpull%2F90&data=02%7C01%7Csimonpj%40microsoft.com%7C5002e529d3
| d145d0cd3908d535a5b7ef%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C63647
| 3908229182766&sdata=dwqEwkLl3ykQjs2PKWJzaV7z2UegZizNLIsf%2F%2FTD2CI%3D&re
| served=0
| 
| 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
| 
| https://na01.safelinks.protection.outlook.com/?url=http%3A%2F%2Fwww.joach
| im-
| breitner.de%2F&data=02%7C01%7Csimonpj%40microsoft.com%7C5002e529d3d145d0c
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