Allow ScopedTypeVariables

[mcandre]

When I try to compile my Fay code, it says:

$ make install
fay ../ios7crypt.hs
fay: ScopedTypeVariables is not enabled

So I added {-# LANGUAGE ScopedTypeVariables, DeriveDataTypeable #-}, but Fay doesn't like the syntax.

$ make install
fay ../ios7crypt.hs
fay: Parse error: {-# LANGUAGE

Can we add {-# LANGUAGE ScopedTypeVariables, DeriveDataTypeable #-} syntax to Fay like GHC uses?

[chrisdone]

Where did you put it in the file?

[chrisdone]

Oh, after module. Yeah, that's not supported in either GHC or Fay. It's just ignored in GHC. haskell-src-exts counts it as a parse error.

[mcandre]

I tried positioning the directive before the module declaration and after. Fay reports a parse error either way.

[bergmark]

[V~/tmp] > cat test.hs 
{-# LANGUAGE ScopedTypeVariables, DeriveDataTypeable #-}
module Main where

import Language.Fay.Prelude

main :: Fay ()
main = return ()
[V~/tmp] > fay test.hs && node test.js
[V~/tmp] > 

OK here

[mcandre]

I modified ios7crypt.hs but fay still fails to compile it.

Trace:

$ fay ios7crypt.hs
fay: ScopedTypeVariables is not enabled

Snippet (Lines 1-7):

-- Allows derivating Typeable and Data
{-# LANGUAGE ScopedTypeVariables, DeriveDataTypeable #-}

module IOS7Crypt where

import Language.Fay.FFI
import Language.Fay.Prelude

...

Specs:

$ fay --version
fay 0.10.1.0

Which version of Fay are you using? How did you build Fay? I used cabal install with no special options.

[bergmark]

Okay this is a bug, the flag is not propagated to ghc, here's a minimal reproduction

{-# LANGUAGE ScopedTypeVariables #-}

module Test where

foo (x :: Int) = x

[bergmark]

OK nope, it is haskell-src-exts that needs extensions = [ScopedTypeVariables]. Also this needs to be handled in the fay compiler, just treat the declaration as if the type wasn't there, should be a simple to fix if anyone wants to give it a shot.

fay: unsupported pattern syntax: x :: Int

[bergmark]

A minor quirk to consider is what this would mean:

f :: Foo
f :: Ptr Foo = ffi "..."

It should probably throw an error.

See #378 for discussion.