relaxed instance rules spec (was: the MPTC Dilemma (please solve))

Ben Rudiak-Gould Benjamin.Rudiak-Gould at
Tue Mar 7 12:51:02 EST 2006

John Meacham wrote:
> On Thu, Mar 02, 2006 at 03:53:45AM -0000, Claus Reinke wrote:
>> the problem is that we have somehow conjured up an infinite
>> type for Mul to recurse on without end! Normally, such infinite
>> types are ruled out by occurs-checks (unless you are working
>> with Prolog III;-), so someone forgot to do that here. why?
>> where? how?
> Polymorphic recursion allows the construction of infinite types if I
> understand what you mean.

No, that's different. An infinite type can't be written in (legal) Haskell. 
It's something like

     type T = [T]

-- Ben

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