[Haskell-cafe] Template Haskell question

17 Apr 2011

      I'm interested if it's possible to use functions from some module without
explicitly importing it. In ghci it's done on the fly, like this:

Prelude> Data.Map.empty
Loading package array-0.3.0.2 ... linking ... done.
Loading package containers-0.4.0.0 ... linking ... done.
fromList []

But without gchi it seems impossible.

I have the file Test.hs:
...
{-# LANGUAGE TemplateHaskell #-}
module Test where
import Language.Haskell.TH
x :: ExpQ
x = global $ mkName "Data.Map.empty"
When I load it in ghci, all works:

$ ghci -XTemplateHaskell Test.hs
*Test> $x
Loading package pretty-1.0.1.2 ... linking ... done.
Loading package array-0.3.0.2 ... linking ... done.
Loading package containers-0.4.0.0 ... linking ... done.
Loading package template-haskell ... linking ... done.
fromList []

But when I try to use it from other module, it fails. File Main.hs:
...
{-# LANGUAGE TemplateHaskell #-}
module Main where
import Test
main = do
  print $x
$ runhaskell Main.hs

Main.hs:5:9:
    Not in scope: `Data.Map.empty'
    In the result of the splice:
      $x
    To see what the splice expanded to, use -ddump-splices
    In the first argument of `print', namely `$x'
    In the expression: print ($x)

--
All the best,
Alexey

[Haskell-cafe] Template Haskell question

Alexey Karakulov