#4949: TH typechecking regression
----------------------------------------+-----------------------------------
Reporter: igloo | Owner:
Type: bug | Status: new
Priority: highest | Milestone: 7.0.2
Component: Compiler (Type checker) | Version: 7.0.1
Keywords: | Testcase:
Blockedby: | Difficulty:
Os: Unknown/Multiple | Blocking:
Architecture: Unknown/Multiple | Failure: None/Unknown
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The 7.0 branch (and HEAD) behaves differently to 7.0.1 on this modules:
{{{
{-# LANGUAGE TemplateHaskell #-}
module Foo where
import Language.Haskell.TH
x :: Int
x = let args = [| show $(varE (mkName "x")) |]
in undefined
}}}
7.0.1 accepted it, while we now get:
{{{
Foo.hs:7:19:
Ambiguous type variable `a0' in the constraint:
(Show a0) arising from a use of `show'
Probable fix: add a type signature that fixes these type variable(s)
In the Template Haskell quotation [| show ($(varE (mkName "x"))) |]
In the expression: [| show ($(varE (mkName "x"))) |]
In an equation for `args': args = [| show ($(varE (mkName "x"))) |]
}}}
This affects these packages:
{{{
CCA
Printf-TH
grammar-combinators
hacanon-light
hamlet
rowrecord
th-lift
web-routes-quasi
}}}
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/4949>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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