Re: [stack] sweetening concatenative syntax

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(‘quadratic: cannot take root of negative argument’)
> ;   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 /

Ah, syntax is fun.

- John
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