skaller wrote:

>>>What about high level optimisations?
>>>
>>>Felix supports this:
>>>
>>>	reduce revrev[t] (x:list[t]): rev (rev x) => x;
>>>      
>>>
>>Haskell (GHC to be precise) allows that too. But is syntactic 
>>term-rewriting, in other words it is *untyped*.
>>    
>>
>
>It's well typed. x:list[t] means x is of type list[t].
>  
>
The *result* is well-typed.  What is the 'type' of the rule (ie the 
'function' reduce) ?  reduce acts on the programming language syntax, 
not on semantic values.

Jacques