[GHC] #11345: Template Haskell's handling of infix GADT constructors is broken
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Thu Jan 7 12:14:33 UTC 2016
#11345: Template Haskell's handling of infix GADT constructors is broken
-------------------------------------+-------------------------------------
Reporter: RyanGlScott | Owner: RyanGlScott
Type: bug | Status: patch
Priority: normal | Milestone:
Component: Template Haskell | Version: 8.1
Resolution: | Keywords:
Operating System: Unknown/Multiple | Architecture:
Type of failure: Incorrect result | Unknown/Multiple
at runtime | Test Case:
Blocked By: | Blocking:
Related Tickets: | Differential Rev(s): Phab:D1744
Wiki Page: |
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Comment (by RyanGlScott):
Replying to [comment:7 jstolarek]:
> There is no such field in `ConDeclGADT` data constructor, so how can we
mark a constructor declaration as infix?
This was my mistake. I thought that infix GADT constructors were marked
with their own constructor ''à la'' `InfixCon`, but that turns out not to
be the case. Instead, GHC simply checks for three properties in a
generalized `PrefixCon`.
> > what happens when you try to splice an infix `GadtC` into source code
in `Convert.hs`?
>
> Indeed, what should happen in such a situation? I believe we should
splice a normal GADT constructor because we have no way of expressing the
infixity.
Luckily, we don't need to express the infixity directly in the `GadtC`, as
it suffices to splice in a `GadtC` with a symbol name and exactly two
arguments, plus a separate fixity declaration. GHC takses care of the rest
(see the test case in Phab:D1744 for proof).
> > A GADT constructor is only considered to be declared infix if (a) it
is an operator symbol, (b) it has two arguments, (c) it has a fixity
declaration.
>
> Can you show me where this happens in code?
These are checked via
[https://git.haskell.org/ghc.git/blob/c78fedde7055490ca6f6210ada797190f3c35d87:/compiler/typecheck/TcTyClsDecls.hs#l1469
tcConIsInfixGADT].
--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11345#comment:8>
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