[plt-scheme] a few questions (was: Scheme questions?)

On Dec 4, 2005, at 8:19 PM, Gregory Woodhouse wrote:

>
> On Dec 4, 2005, at 5:08 PM, Matthias Felleisen wrote:
>
>>
>>> I don't know if the Y combinator had been devised when McCarthy was
>>> trying to computerize recursion theory,
>>
>> 1930s.
>
> Are you sure?

Yes.

> I know lambda calculus was developed in the 1930's, but didn't Dana 
> Scott develop domain theory (where you get fixed points for continuous 
> functions) in the 1970's.

The Y combinator is a syntactic idea, not a semantic one. Yes, it took 
people some 35 years to develop the semantics of the LC but that 
doesn't prevent anybody from doing and using Y, the S/K stuff, and many 
more purely syntactic things.

> Incidentally, here's something I wrote for another list after seeing 
> the fix point operator in Haskell. I still have a hard time believing 
> it actually worked (and yes, I know, it's an explicit definition, no 
> Scott topology or continuous functions):

Yes, I know this kind of stuff :-)

-- Matthias