Re: [Haskell-cafe] Termination of substitution

2008-03-20 Thread Neil Mitchell
Hi Thanks for the interesting comments. Its looks like learning some of the basics about System Fw is probably the way forward. However GHC goes beyond Fw by adding data types letrec This blows strong normalisation out of the water. (Assuming you have reasonable rules

RE: [Haskell-cafe] Termination of substitution

2008-03-13 Thread Simon Peyton-Jones
As Stefan says, System Fw is strongly normalising. This is a remarkable result because (as you observe) it's very non-obvious how to prove it. However GHC goes beyond Fw by adding data types letrec This blows strong normalisation out of the water. (Assuming you have reasonable

Re: [Haskell-cafe] Termination of substitution

2008-03-12 Thread Taral
On 3/12/08, Neil Mitchell [EMAIL PROTECTED] wrote: However, I don't believe this expression is type safe in Haskell. Using higher-order polymorphism: f (x :: forall a. a - a) = x x -- Taral [EMAIL PROTECTED] Please let me know if there's any further trouble I can give you. -- Unknown

Re: [Haskell-cafe] Termination of substitution

2008-03-12 Thread Stefan O'Rear
On Wed, Mar 12, 2008 at 09:05:03PM +, Neil Mitchell wrote: Hi I'm trying to show that a system of rules for manipulating Haskell expressions is terminating. The rules can be applied in any order, to any subexpression - and there is a problem if there is any possible infinite sequence.

Re: [Haskell-cafe] Termination of substitution

2008-03-12 Thread Stefan O'Rear
On Wed, Mar 12, 2008 at 02:30:41PM -0700, Taral wrote: On 3/12/08, Neil Mitchell [EMAIL PROTECTED] wrote: However, I don't believe this expression is type safe in Haskell. Using higher-order polymorphism: f (x :: forall a. a - a) = x x Interestingly, this doesn't work - f is a