Instantiating a type with fresh, flexi type variables

[Dr. ÉRDI Gergő]

Hi Simon,

Here's what I wrote earlier about this to someone who contacted me in
private (name withheld because I don't know why he contacted me off-list):

"""
So the code in question is this:
https://github.com/gergoerdi/ghc/commit/f874f8#L5R749

and the part that feels fishy to me is tcInstTypes, both the implementation
and the fact that I have to take care of this manually. I guess the right
solution would involve doing something differently in
https://github.com/gergoerdi/ghc/commit/244b9#L3R43
so that the types in "rhs_ty" and "args" are correctly generalized. But I
haven't been able to find out how that would be done.
"""

I'm replying to your other questions in a separate, private mail.

Thanks,
Gergo
On Aug 20, 2013 6:14 AM, "Simon Peyton-Jones" <simonpj at microsoft.com> wrote:

> I'm a bit puzzled that you don't have a *quantified* type, something like
>         forall abc.  ty1 -> ... -> tyn -> ty
> to instantiate. I'm a bit suspicious about instantiating all the random
> free variables of a type (or types). We should talk now I'm back in
> circulation.   What time zone are  you in?  What's your skype id? (Mine is
> simonpj0)
>
> simon
>
> |  -----Original Message-----
> |  From: ghc-devs [mailto:ghc-devs-bounces at haskell.org] On Behalf Of Dr.
> ERDI
> |  Gergo
> |  Sent: 08 August 2013 18:37
> |  To: ghc-devs at haskell.org
> |  Subject: Instantiating a type with fresh, flexi type variables
> |
> |  For my pattern-synonyms branch (see prev. email) I had to write the
> |  following function, incl. making TcValidity.fvTypes public:
> |
> |  tcInstTypes :: [TcType] -> TcM [TcType]
> |  tcInstTypes tys
> |     = do { let tvs = fvTypes tys
> |          ; (_, _, subst) <- tcInstTyVars tvs
> |          ; return $ map (substTy subst) tys }
> |
> |  I'm surprised I had to write this myself, and this made me wonder if
> |  there's a much better way to handle cases where I have some kind of
> |  definition which has some inferred type, and then various use sites
> |  of that definition must all have types that can be unified with this
> |  original inferred type.
> |  Is there?
> |
> |  Thanks,
> |       Gergo
> |
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>
>
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