Permitting trailing commas for record syntax ADT declarations

[Simon Peyton Jones]

| presently), whilst requiring a pragma means either making the parser
| code really messy "everywhere" there's a comma, or having lots of
| duplication there.

I don't understand this at all.  The standard way is simply to parse the comma(s) always, record the presence of trailing comma(s) in the syntax tree, and then complain/reject in the renamer if the extension is not enabled.  That does not make the parser really messy anywhere, I think.  You might want a new HsSyn data type for "list with possible leading or trailing commas":

  data HsCommadList a 
    = HCL
         Int -- Number of leading commas
         [a]
         Int -- Number of trailing commas

Simon

| 
| And giving it some thought, I'd argue for going more or less the same
| route with regards to patches for a pragma. I.e. add an initial patch
| that adds the pragma itself & leading commas for imports/exports, and
| then submit a bunch of small commits to augment the pragma to
| phabricator, and update the Wiki accordingly.
| 
| 
| In any event, I'll have to get everything working, so you'll have
| plenty of time meanwhile to decide on this issue.
| - --
| Alexander
| alexander at plaimi.net
| https://secure.plaimi.net/~alexander
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