addTopDecls fails with typed Template Haskell

The following untyped Template Haskell works as expected:

--- AddTopDecls.hs ---
{-# LANGUAGE TemplateHaskell #-}
{-# LANGUAGE QuasiQuotes     #-}

module AddTopDecls where

import Language.Haskell.TH
import Language.Haskell.TH.Syntax

importDoubleToDouble :: String -> ExpQ
importDoubleToDouble fname = do
    n <- newName fname
    d <- forImpD CCall unsafe fname n [t|Double -> Double|]
    addTopDecls [d]
    varE n

--- Main.hs ---
{-# LANGUAGE TemplateHaskell #-}

module Main where

import AddTopDecls

main :: IO ()
main = do
    let sin' = $(importDoubleToDouble "sin")
        cos' = $(importDoubleToDouble "cos")
    --
    print (sin' 0)
    print (cos' pi)

However it fails if I convert to the equivalent typed version:

--- AddTopDecls.hs ---
{-# LANGUAGE TemplateHaskell #-}
{-# LANGUAGE QuasiQuotes     #-}

module AddTopDecls where

import Language.Haskell.TH
import Language.Haskell.TH.Syntax

importDoubleToDouble :: String -> Q (TExp (Double -> Double))
importDoubleToDouble fname = do
    n <- newName fname
    d <- forImpD CCall unsafe fname n [t|Double -> Double|]
    addTopDecls [d]
    unsafeTExpCoerce (varE n)

--- Main.hs ---
{-# LANGUAGE TemplateHaskell #-}

module Main where

import AddTopDecls

main :: IO ()
main = do
    let sin' = $$(importDoubleToDouble "sin")
        cos' = $$(importDoubleToDouble "cos")
    --
    print (sin' 0)
    print (cos' pi)

With the error:

> ghci Main.hs -ddump-splices
GHCi, version 8.2.0.20170404: http://www.haskell.org/ghc/  :? for help
[1 of 2] Compiling AddTopDecls      ( AddTopDecls.hs, interpreted )
[2 of 2] Compiling Main             ( Main.hs, interpreted )
Main.hs:9:19-44: Splicing expression
    importDoubleToDouble "sin" ======> sin_a4s2
Main.hs:1:1: Splicing top-level declarations added with addTopDecls
  ======>
    foreign import ccall unsafe "sin" Main.sin :: Double -> Double

Main.hs:9:19: error:
    • GHC internal error: ‘sin_a4s2’ is not in scope during type checking, but it passed the renamer
      tcl_env of environment: [a4dl :-> Identifier[sin'::t1, TopLevelLet [] False],
                               a4dm :-> Identifier[cos'::t1, TopLevelLet [] False],
                               r4cW :-> Identifier[main::IO (), TopLevelLet]]
    • In the expression: sin_a4s2
      In the result of the splice:
        $importDoubleToDouble "sin"
      To see what the splice expanded to, use -ddump-splices
      In the Template Haskell splice $$(importDoubleToDouble "sin")
  |
9 |     let sin' = $$(importDoubleToDouble "sin")
  |                   ^^^^^^^^^^^^^^^^^^^^^^^^^^

Tested with 7.10.3, 8.0.2, and 8.2.0-rc1.

Unfortunately I can't use untyped TH in my real use case, so if you have any suggestions for a workaround that would also be great.

Trac metadata

Trac field	Value
Version	8.2.1-rc1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Template Haskell
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