В письме от 27 апреля 2013 18:55:16 пользователь Corentin Dupont написал:

Hi Cafe,
can I ask the compiler to display the type of an inferred value during compile time?
It would be great if I can output a string during compilation with the type.
A little bit like running :type in GHCi, but without GHCi... Because running GHCi is sometime painful (I have to clean my code first).

I'm thinking of something like:

main :: IO ()
main = do
   a <- someCode
   displayTypeAtCompileTime a
   return ()

$ ghc -c test.hs
test.hs:4:3: your type is: Foo

Thanks,
Corentin

Hi.

What about TemplateHaskell? Smth like:

{-# LANGUAGE TemplateHaskell #-}

module DisplayType where

import Language.TH

displayTypeAtCompileTime :: Name -> Q Exp

displayTypeAtComileTime name = do

reified <- reify name

-- inspect reified structure, see TH haddock documentation

runIO $ putStrLn $ show theType

[| undefined |] -- you need to return some expression; since you are not to use it's value, it may be even undefined, it seems.

###

{-# LANGUAGE TemplateHaskell #-}

module Main where

import DisplayType

main = do

...

$displayTypeAtCompileTime 'a

...

WBR, Ilya Portnov.