Meta-point: backward compatibility

Neil Mitchell ndmitchell at
Thu Apr 24 04:21:41 EDT 2008


I think Henrik's criteria are pretty close to perfect.

>  As I have argued before on the committee list, I also think we should *not*
> worry about backwards incompatible changes too much in cases where a simple
> automatic translation from H98 to H' code is possible.  Even for a large
> project, it is IMHO no big hardship to run a H98->H' translator over all
> Haskell sources.

Some questions:

1) Will I (the programmer) have to mode switch in painful ways between
H98 and H'? Do I have to learn a pile of exceptions, or is there some
common rule that works? (i.e. removing n+k is fine since I just don't
learn it, changing the fixity of $ is not since I need to know both)

2) Will tool T (the translator) work on academic papers that have
previously been published.

3) Will tool T handle all of GHC's extensions.

4) Will tool T deal with things like CPP, hsc, trhsx, happy, alex
etc... - all these file formats which include embedded Haskell.

5) Will tool T ever exist.

I think the answer to 2-5 is nearly certainly going to be "No". I
don't think the relevance of a conversion tool should even be
considered until some person steps forward and says without doubt that
_they_ will write the converter. Even if they did there very best, it
still won't be trivial to use in all cases.

> As John Launchbury has said, given Haskell's current rise in popularity, anything that
> we do not fix with H' will be much harder, if not impossible, to fix in the future.

That is a very good point. Perhaps we're already a little too late.



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