Re: [stack] sweetening concatenative syntax

On 19/3/08 6:06 PM, "John Nowak" <[email protected]> wrote:

> 
> On Mar 18, 2008, at 10:17 PM, Manfred Von Thun wrote:
> 
>> quad turns [C:num, B:num, A:num | R] into [[P:num,N:num] list | R] :-
>> Diff is B*B -$*A*C,
>> (   Diff < 0.0,
>> ->  write(Œquadratic: cannot take root of negative argument¹)
>> ;   Root is sqrt(Diff),
>>    P is (0-B+Root)/(2*A),
>>    N is (0-B-Root)/(2*A)
>> ).
> 
> Here's another version of the above with a syntax more suited to a
> concatenative language:
> 
> quad a b c = p n
>     where d = b 4 a c * * -
>           r = d 0 >= [d sqrt] ["quad: sqrt of negative" error] if
>           x = 2 a *
>           p = b r - x /
>           n = b r + x /
> 

Yes, I entirely agree. What I gave was the Prolog program, and if
someone implementing a concatenative language has to choose
a notation for arithmetic and other types, our form would be best.
But to get the unification for the variables in the input and the
output stacks, you have to write a little Prolog ­ and that is not so easy.
So I just used an excellent existing Prolog, SWI-prolog.




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