Re: [Haskell-cafe] ScopedTypeVariables in let-bindings (not where-bindings!) and bug 4347

On Sat, May 21, 2011 at 10:49, Paolo Giarrusso wrote:

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On Sat, May 21, 2011 at 10:17, Paolo G. Giarrusso

wrote:

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First, thanks to you and everybody for the alternative. But I'm still convinced that the syntax is supposed to work, and you're just workarounding the bug.

Hm, I think we have differing expectations; the syntax everyone presented is the one that is normally used for such things in ghci, and while perhaps

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one you tried is supposed to work, it's a bit unusual and therefore

On Sat, May 21, 2011 at 16:27, Brandon Allbery wrote: the probably

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not very well tested.

Yes, it was my guess as well - and for some reason I missed the usual syntax. A sincere question about the usual syntax: where do you learn it? It's

It's just the desugaring of layout, with the braces being optional because it's all on one line. Since you can't use layout in ghci, you have to manually convert. It is perhaps not entirely obvious (I was a bit surprised when, as a complete Haskell newbie, I decided to try it and it worked) that you can specify types in both let and where clauses in the same way you do at the top level:

let a :: a -> a a = a a where b :: b -> b b = b b

which in its non-layout version is

let { a :: a -> a; a = a a } where { b :: b -> b; b = b b }

(using the braces here because it's a bit ambiguous; I think H'2010 fixed that though)