Jim Apple
Mon, 08 Jan 2007 05:51:45 -0800
On 1/8/07, Tomasz Zielonka <[EMAIL PROTECTED]> wrote:
On Mon, Jan 08, 2007 at 08:02:36AM -0500, Lennart Augustsson wrote: > So it sounds to me like the (terminating) type > checker solves the halting problem. Can you please explain which part > of this I have misunderstood? Perhaps you, the user, have to encode the proof of halting in the way you construct the term?
The Terminating datatype takes three parameters: 1. A term in the untyped lambda calculus 2. A sequence of beta reductions 3. A proof that the result of the beta reductions is normalized. Number 2 is the hard part. For a term that calculated the factorial of 5, the list in part 2 would be at least 120 items long, and each one is kind of a pain. GHC's type checker ends up doing exactly what it was doing before: checking proofs. Jim _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe