Re: [Haskell-cafe] Template haskell: This pattern-binding binds no variables

I need this unique iname in other places as well. letE would work, right. I'll file a bugreport later then, Thanks!

I think it's a bug. Maybe the fix is similar to the one done for https://ghc.haskell.org/trac/ghc/ticket/9127.

Assuming you only need that unique name ('ohNoes :: Name) after you bind it with the let, you can avoid the warning with:

sample :: Q Exp sample = [| let ohNoes = "Teh warning!" in print $( varE 'ohNoes ) |]

Or you could use letE instead of the brackets, as we had to with ghc < 7.8 when PatQ splices were added.

Regards, Adam

On Sun, Dec 21, 2014 at 3:50 AM, Michael Baikov wrote:

...

I'm trying to introduce a new local variable to some scope, in this example this scope is represented by print $( varE ohNoes)

Everything works as expected, but I'm getting a warning message which I don't seem quite right to me. Am I doing anything wrong?

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

module Blah where

import Language.Haskell.TH

sample :: Q Exp sample = newName "ohNoes" >>= \ohNoes -> [| let $( varP ohNoes ) = "Teh warning!" in print $( varE ohNoes ) |]

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

module Main where import Blah

main :: IO () main = $( sample )

---- output ----

Blah.hs:8:49: Warning: This pattern-binding binds no variables: $(varP ohNoes) = "Teh warning!"

sample ======> let ohNoes_a2Al = "Teh warning!" in print ohNoes_a2Al _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe