#5452: reify yields incorrect TupleT at higher-kinds
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Reporter: nicolas.frisby | Owner:
Type: bug | Status: new
Priority: normal | Component: Template Haskell
Version: 7.2.1 | Keywords:
Testcase: | Blockedby:
Os: Unknown/Multiple | Blocking:
Architecture: Unknown/Multiple | Failure: GHC rejects valid program
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Line 1175 of changeset:0237ed6762fc86d0eb5db02a8e02ebe35d8d7272 introduces
a bug where reify yields an application of `TupleT` where its argument is
too small when the type being reified is of a higher-kind than `*`.
For example, in the `Applicative` instance for `((,) a)`; the `(,)` gets
reified as `TupleT 1` instead of `TupleT 2`.
Here's some code that duplicates its `C` instance to be a `D` instance.
{{{
{-# LANGUAGE TemplateHaskell, KindSignatures, FlexibleInstances #-}
module ReifyTupleBug where
import Language.Haskell.TH
class C (f :: * -> *)
class D (f :: * -> *)
instance C ((,) Int)
reify ''C >>= \(ClassI _ [i]) ->
return [InstanceD (ci_cxt i) (foldl AppT (ConT ''D) (ci_tys i)) []]
}}}
It results in a kind mis-match:
{{{
ReifyTupleBug.hs:13:1:
Kind mis-match
The first argument of `D' should have kind `* -> *',
but `Int' has kind `*'
In the instance declaration for `D Int'
Failed, modules loaded: none.}}}
I'm not sure how `reify_tc_app` should be adjusted; perhaps it needs to
know the kind at which it is operating and then increment `n_tys` based on
the number of arrows?
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/5452>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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