[Haskell-cafe] PatternSignatures (rant)

Neil Mitchell ndmitchell at gmail.com
Wed Apr 8 03:25:55 EDT 2009


> why has "PatternSignatures"
> been renamed to "ScopedTypeVariables" (in ghc-6.10)?

It's unfortunate that 6.8 doesn't have ScopedTypeVariables and 6.10
warns on PatternSignatures. It would have been nice if you could
support N.M and N.M+2 with the same code without having to turn off

> show me the alleged "type variable" in this code:
> do x :: Int <- [ 1 .. 10 ] ; return $ x^2
> and why on earth do I need to use a language extension at all
> to get to the most basic thing of declarative programming:
> to declare the type of an identifier?

Because it isn't in Haskell 98, and GHC (very kindly) only accepts
Haskell 98 by default. By doing so they've kept the standard alive,
and we should be very grateful for this. I think this is a guaranteed
feature for H', it's really an oversight that it isn't in H98.



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