TCO examples

[infradig]

$ cat w.pl
main(N) :- N > 0, N1 is N-1, main(N1).

$ cat v.pl
% No local vars & no structures, yet not recovered...

zx81(X, Y) :- Y is (X*75+74) mod 65537.
main(0) :- !.
main(I) :- zx81(I, _), I2 is I-1, main(I2).

$ cat y.pl
f(0) :- !, fail.
f(_).
main(N) :- f(N), N1 is N-1, main(N1).

$ cat z.pl
f(X) :- X > 0, X=Y.
main(N) :- f(N), N1 is N-1, main(N1).

All these examples run in constant memory with SWI Prolog:

$ time swipl -g 'main(100000000);halt' w.pl

With Trealla only v.pl does not.

[flexoron]

zx81(X,Y) :- Y is X*1.
main(0) :- !.
% main(I) :- zx81(I,I), I2 is I-1, main(I2). % Good
% main(I) :- zx81(I,M), I2 is I-1, main(I2). % Bad, Var M eats memory
% main(I) :- zx81(I,_), I2 is I-1, main(I2). % Bad, Var _ eats memory

[infradig]

Yes, it's the call to xz81/2 (when you get var/var unification) that causes main/1 not to be TCO. I know why just haven't worked out a solution that doesn't break another test, there may be 2 things to fix.

On Sat, May 25, 2024 at 12:21 PM flexoron @.***> wrote:

zx81(X,Y) :- Y is X*1. main(0) :- !. % main(I) :- zx81(I,I), I2 is I-1, main(I2). % Good % main(I) :- zx81(I,M), I2 is I-1, main(I2). % Bad, Var M eats memory % main(I) :- zx81(I,), I2 is I-1, main(I2). % Bad, Var eats memory

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