[mercury-users] Newbie problem. :)

[Rob]

Hello everybody.

I have a week inbetween exams, so I thought I would take some time off
from studying and work on learning Mercury.
I thought I would try something simple, making an insertion sort for a
list of integers. However, if you think I could create code that
compiles, then you are mistaken. :D
heh. I found a few silly errors that I had made, and worked out the hard
way that "insert" is allready defined somewhere in the standard library.
heh.

The following is my code, and then I'll paste the error I am getting.

--------
% Lets see if I can't do some sorting.

:- module blah.
:- interface.

:- import_module io.
:- pred main(io__state, io__state).
:- mode main(di, uo) is det.

:- implementation.

:- import_module list, int.

:- pred insertion_sort(list(int), list(int)).
:- mode insertion_sort(in, out) is det.

:- pred my_insert(int, list(int), list(int)).
:- mode my_insert(in, in, out) is det.               <-- Line 18

main -->
	{ X = [4,2,3,1] },
	{ insertion_sort(X, Y) },
	io__write(Y),
	io__nl.

insertion_sort(X, Y) :-
	(
	    X = [Hd | Tl],
	    insertion_sort(Tl, Z),
	    my_insert(Hd, Z, Y)
	;
	    X = [],
	    Y = []
	).

my_insert(X, Y, Z) :-
	(
	    Y = [Hd | Tl],
	    (
		X =< Hd,                  <-- Line 40
		Z = [X | [Hd | Tl]]
	    ;
		X > Hd,
		my_insert(X, Tl, W),
		Z = [Hd | W]
	    )
	;   
	    Y = [],
	    Z = [X]
	).

-------
[zharradan at blacksand tmp]$ m -E blah.m
blah.m:018: In `my_insert(in, in, out)':
blah.m:018:   error: determinism declaration not satisfied.
blah.m:018:   Declared `det', inferred `nondet'.
blah.m:040:   call to `=<(in, in)' can fail.
blah.m:043:   call to `>(in, in)' can fail.
blah.m:042:   Disjunction has multiple clauses with solutions.


I am obviously missing something here, but I thought this was the way
things were supposed to work - part of the disjunction fails, and it
checks against the rest..

Help. :)

Thanks,
Rob
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