Re: ANNOUNCE: GHC 5.03.20020410 snapshot released

18 Apr 2002


      Am Donnerstag, 18. April 2002 14:12 schrieb Simon Marlow:
...
...
Ralf Hinze  writes:
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BTW, does this version support rank-n types?
IIRC the previous snapshot did.  So presumably this one does
too?
Yes, it does.
Simon
That's what I feared ;-). Ok, here is my first attempt at defining
a rank-3 function (code attached). ghci responds
---
ralf/Haskell> ghci -v -fglasgow-exts Rank3.lhs
   ___         ___ _
  / _ \ /\  /\/ __(_)
 / /_\// /_/ / /  | |      GHC Interactive, version 5.03.20020410, for Haskell 
98.
/ /_\\/ __  / /___| |      http://www.haskell.org/ghc/
\____/\/ /_/\____/|_|      Type :? for help.

Glasgow Haskell Compiler, Version 5.03.20020410, for Haskell 98, compiled by 
GHC version 5.03.20020410
<...>
*** Typechecker:

Rank3.lhs:20:
    Illegal polymorphic type: forall b1 b2.
                              (b1 -> b2) -> h1 f1 b1 -> h2 f2 b2
    In the type: forall h1 h2 a1 a2.
                 (forall f1 f2.
                  (forall c1 c2. (c1 -> c2) -> f1 c1 -> f2 c2)
                  -> forall b1 b2. (b1 -> b2) -> h1 f1 b1 -> h2 f2 b2)
                 -> (a1 -> a2) -> HFix h1 a1 -> HFix h2 a2
    While checking the type signature for `mapHFix'
---
Do I have to hoist the forall quantifiers in bla -> forall a . blub myself? At
least, the code typechecks then.

Cheers, Ralf