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,
CorentinHi.
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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