The (->) type doesn't survive a TH quote-splice roundtrip

You can roundtrip function types like Bool -> Bool through Template Haskell splicing:

$ /opt/ghc/8.2.2/bin/ghci -XTemplateHaskell
GHCi, version 8.2.2: http://www.haskell.org/ghc/  :? for help
Loaded GHCi configuration from /home/rgscott/.ghci
λ> :m + Language.Haskell.TH
λ> :k $([t| Bool -> Bool |])
$([t| Bool -> Bool |]) :: *

However, GHC doesn't offer the same courtesy to (->) applied prefix, as in the following example:

λ> :k $([t| (->) Bool Bool |])

<interactive>:1:3: error:
    • Illegal type constructor or class name: ‘(->)’
      When splicing a TH type:
        GHC.Prim.(->) GHC.Types.Bool GHC.Types.Bool
    • In the untyped splice: $([t| (->) Bool Bool |])

One way to fix this would be to consistently desugar (->) to ArrowT in DsMeta (instead of leaving it as GHC.Prim.(->)).

Trac metadata

Trac field	Value
Version	8.2.2
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Template Haskell
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