[Haskell] SYB Documentation is inconclusive.
Arthur van Leeuwen
arthurvl at cs.uu.nl
Thu Nov 23 18:16:20 EST 2006
On 23-nov-2006, at 23:22, Ralf Lammel wrote:
> constrFields eventually returns some mangled strings from the
> abstract syntax tree; see ghc-fptools/ghc/compiler/basicTypes/
> DataCon.lhs; and that abstract syntax promises to be order-preserving.
> It says (not surprisingly):
> dcFields :: [FieldLabel],
> -- Field labels for this constructor, in the
> -- same order as the argument types;
> -- length = 0 (if not a record) or dataConSourceArity.
> gmapQ maps the children to results. Since it is a map, it is order-
> preserving. There is not even any associatively business in the
> case of gmapQ (as opposed to gmapQl and gmapQr).
> So zipping together results from gmapQ and constrFields plus
> handling the special case of non-record types, should be just fine,
> no? What could possibly go wrong? Perhaps you are saying that the
> documentation of constrFields should promise explicitly that it
> does not mangle order?
Such a promise would have been nice. I assumed that The Right Thing
no magic reorderings) would happen, but it was unclear from the
the haddock documentation.
I should've looked into the source, of course, as that is the definitive
> Let me know if I don't get what you are after ... perhaps in the café.
You have fully understood and explained. Glad to see that The Right
is done. Now I can safely go and let my code into the hands of
With regards, Arthur van Leeuwen.
/\ / | arthurvl at cs.uu.nl | Work like you don't need
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