RE: Partial type sigs

| avoid breaking existing programs. We might as well make named | wildcards lexically scoped by default, not even opt-out (as was the | case in my initial proposal). I don't object strongly, so long as the user manual is very clear on the question, and mentions the inconsistency with ordinary type variables. | About using a Maybe for sig_id to fix 10045: I tried it out, and your | solution does indeed fix it. In order for TcSigInfo to still implement | NamedThing, I used an 'Either Name TcId' instead of a 'Maybe TcId'. Do | you prefer a separate data type for this instead of an Either? (Please | come up with a good name for it in that case :) Better: * Remove instance NamedThing TcSigInfo * Add a field sig_name :: Name, and use it instead of getName in tcTySigs Comment that if sig_id = Just f, then sig_name = idName f * Leave the sig_id field as (Maybe TcId). It needs a pretty big comment. Actually sig_poly_id would be a better name for the field. | Unfortunately, some of my tests started failing, so I'll post | something on Phabricator as soon as I have worked out the kinks. OK thank you. Ping me when ready Simon | | | Cheers, | Thomas | | | | > Sorry to make such a misleading post. | > | > Simon | > | > | -----Original Message----- | > | From: dominique.devriese@gmail.com | > [mailto:dominique.devriese@gmail.com] | > | On Behalf Of Dominique Devriese | > | Sent: 05 February 2015 20:13 | > | To: Simon Peyton Jones | > | Cc: Thomas Winant; ghc-devs@haskell.org; Frank Piessens | > | Subject: Re: Partial type sigs | > | | > | Simon, | > | | > | 2015-02-05 17:44 GMT+01:00 Simon Peyton Jones | > : | > | > 3. It interferes with generalisation. | > | > | > | > For (3), consider | > | > | > | > let f :: _a -> _a | > | > | > | > f xs = reverse xs | > | > | > | > in (f True, f ‘x’) | > | > | > | > Here, f gets the type f :: forall b. [b] -> [b], and _a is | unifed | > with | > | [b]. | > | > | > | > So it simply doesn’t make sense for _a to appear in the body. | > | > What | > | would it | > | > mean to say | > | > | > | > let f :: _a -> _a | > | > | > | > f xs = reverse xs | > | > | > | > in (f (True :: _a), f ‘x’) | > | | > | Isn't this a different case than Thomas' example? As I understand | > | it, an equivalent of his example would have the wildcard in scope | in | > | the body of f, not in the body of the let. Something like this: | > | | > | let f :: _a -> _a | > | f xs = reverse (xs :: _a) | > | in (f [True], f "x") | > | | > | or | > | | > | let f :: _a -> _a | > | f xs = let ys :: _a | > | ys = tail xs | > | in reverse ys | > | in (f [True], f "x") | > | | > | I agree with what you say about _a being in scope in the body of | the | > | if, but I don't see a problem with _a being in scope in the body | of | > f. | > | Do you? | > | | > | Note also that I haven't yet checked which of both is actually | > | implemented. | > | | > | Regards, | > | Dominique | | Disclaimer: http://www.kuleuven.be/cwis/email_disclaimer.htm