Permitting trailing commas for record syntax ADT declarations

Simon Peyton Jones simonpj at
Tue Sep 23 07:31:58 UTC 2014

| > have a language extension TrailingCommas (or something) to enable
| > the extension
| For clarification: are you overruling the "do we sneak it in HEAD or
| use pragma(s)"-vote and telling me to do the latter?

Well, it *is* a language extension, exactly like lots of other language extensions, isn't it? (E.g. UnicodeSyntax.)  What alternative action, exactly, are you proposing?   Why do you propose to treat it differently to other language extensions?  I would be reluctant to simply add it without any indication; then GHC would accept non-Haskell 2010 programs.  And we have not done that with other extensions.


| If we can sneak it into HEAD (this is @ you Johan, too), I suggest
| that someone applies my patches to make import and export lists
| support leading commas (presently they only support trailing commas,
| per the report) -- and following this I can just send a bunch of
| "Permit leading/trailing ',' in Foo" patches to Phabricator, and you
| guys can bikeshed over there about which ones you actually want to
| commit. ;-)
| If I am to go down the pragma route, I guess I can make a
| RudundantCommas pragma or something like that, that implements
| trailing commas for imports/exports, and leading/trailing commas for
| the suggestions in this thread.
| I'm +1 on the GHC HEAD route, but I'm not exactly violently opposed to
| the pragma route either.
| - --
| Alexander
| alexander at
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| Comment: Using GnuPG with Thunderbird -
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