Constructing TH types
nicolas.frisby at gmail.com
Sun Oct 7 18:24:11 CEST 2012
The issue you had with applications of the  type seems to be more
insidious than my last email made it out to be. This expression
( $(return $ ConE (mkName "")) ::
$(return $ ConT (mkName "") `AppT` ConT ''Char)
fails with " is applied to too many arguments". I'm thinking that
the "" in the type is being resolved somehow to the the  data
constructor, not the  type constructor.
This seems specific to ; the following works for tuples, even though
the data and type constructor also share a string name.
$(return $ ConE (mkName "(,)") `AppE` LitE (CharL 'c') `AppE` LitE
(CharL 'a')) ::
$(return $ ConT (mkName "(,)") `AppT` ConT ''Char `AppT` ConT ''Char)
I haven't yet narrowed down where the mkName'd string is
(inappropriately?) resolved in the GHC source.
Eric, special-casing for ArrowT probably avoids this problem for you.
The only thing to glean from this email is that you ideally wouldn't
need to worry about the special-casing for your current application —
I think there's a TH bug at play, though I haven't found an open GHC
ticket for it and it may very well still be a known issue.
On Sun, Oct 7, 2012 at 10:15 AM, Eric M. Pashman <eric.pashman at gmail.com> wrote:
> Nicolas, thanks for the welcome, and thanks for pointing out the additional 'Type' constructors!
> I'd looked over the available constructors, but apparently not very well. The 'ListT', 'TupleT', 'ArrowT', etc., constructors are precisely what I need to make this work in a straightforward fashion.
> So I don't actually have a problem making the right 'Name' value, just a problem reading the TH source. Well, that's that. ...
> Many thanks,
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