Proposal: Turn on ScopedTypeVariables by default

Andrew Farmer afarmer at
Mon Feb 23 17:59:22 UTC 2015

I have often thought the same thing. This is probably the language
extension I enable the most... a quick grep shows about 40% of my

I'm guessing the problem is that its not Haskell 98/2010? I think GHC
has a policy to do only what the spec says by default. Is that still
true now that AMP is implemented?

You could just always include it in the 'extensions' field of your
cabal file. Then it will apply to your whole project.

On Mon, Feb 23, 2015 at 11:45 AM, David Feuer <david.feuer at> wrote:
> I know this will be controversial, because it can break (weird) code and
> because it's not Haskell 2010, but hey, you can't make brain salad without
> breaking a few heads. ScopedTypeVariables is just awesome for two
> fundamental reasons:
> 1. It lets you write type signatures for more things.
> 2. It lets you write more precise type signatures for many things.
> As a consequence of those two,
> 3. It helps you get much better error messages from the type checker.
> And for all that,
> 4. It's really easy to use.
> What do other people think?
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