[core libraries] Re: Tightening up on inferred type signatures

[Edward Kmett]

You can wind up in perfectly legitimate situations where the name for the
type you are working with isn't in scope, but where you can write a
combinator that would infer to have that type. I'd hate to lose that.

It is admittedly of marginal utility at first glance, but there are some
tricks that actually need it, and it can also arise if a type synonym
expands to a type that isn't exported or brought into scope, so trying to
push this line of reasoning too far I is possibly not too productive.

Parts of lens, constraints and probably a few other packages I maintain
would break as hard data points.

-Edward


On Tue, Apr 22, 2014 at 2:44 AM, Simon Peyton Jones
<simonpj at microsoft.com>wrote:

> | Independent of language extensions, what about types and classes whose
> | names are not in scope.  Is there an implicit "... if you import all
> | the relevant symbols" and the end of the rule?
>
> Good point.  I'm honestly unsure how far to push this one!  (It'd be
> relatively easy to check whether they were in scope and complain if not,
> but ...)
>
> Simon
>
> | -----Original Message-----
> | From: haskell-core-libraries at googlegroups.com [mailto:haskell-core-
> | libraries at googlegroups.com] On Behalf Of David Mazieres
> | Sent: 22 April 2014 00:41
> | To: Simon Peyton Jones; Haskell Libraries (libraries at haskell.org);
> | core-libraries-committee at haskell.org; GHC users
> | Subject: [core libraries] Re: Tightening up on inferred type signatures
> |
> | Simon Peyton Jones <simonpj at microsoft.com> writes:
> |
> | > GHC generally obeys this rule
> | >
> | > * If GHC infers a type f::type, then it's OK for you to add a type
> | > signature saying exactly that.
> |
> | Independent of language extensions, what about types and classes whose
> | names are not in scope.  Is there an implicit "... if you import all
> | the relevant symbols" and the end of the rule?
> |
> | David
> |
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