[Haskell-cafe] Display an inferred type during compilation

[Corentin Dupont]

Thanks all for your solutions!
Here is a summary:

- floating a value to the top level; then with -Wall GHC will give the type
since we didn't give a value,
- adding :: () to the value to check, GHC will complain equally,
- using TemplateHaskell (hereunder),
- waiting for the release of the next GHC with TypeHoles.

Corentin

On Sat, Apr 27, 2013 at 8:46 PM, Ilya Portnov <portnov at iportnov.ru> wrote:

> **
>
> 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.
>
>
>
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