[Haskell-cafe] What does the `forall` mean ?

Andrew Coppin andrewcoppin at btinternet.com
Thu Nov 12 05:36:32 EST 2009

Dan Piponi wrote:
> To use these types with ghc you need to use the compilation flag
> -XExistentialQuantification.

Or, more portably, add {-# LANGUAGE ExistentialQuantification #-} at the 
top of the source file. It should now compile in any computer that 
supports this feature without any special command-line flags.

> There's more to be found here:
> http://www.haskell.org/haskellwiki/Existential_typ

Amusingly, half of this article is still the text that I wrote. ;-)

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