Peter Van Roy wrote:
Rusreg wrote:
Hello.
The functions in list module are determinstic. For example I want to
use the List.append function as nondeterministic for parsing string,
but it don't work:
Str in
List = {List.append "(" Str}
I found the nondet. realization of this function in Internet:
proc {Append L1 L2 L3}
dis L1=nil L2=L3
[] X M1 M3 in
L1=X|M1 L3=X|M3 {Append M1 L2 M3}
end
end
and it work fine. Why the functions in List is deteministik? E.g. the
same function (append) of Curry language is nondetermenistik.
Another point about nondeterministic functions: the use of 'dis' is
deprecated in Mozart. You should use 'choice' instead. The reason has
to do with Prolog-style versus constraint-style programming. Prolog
programs basically do generate and test (enumerate and then prune).
Constraint programs do pruning before enumeration (using propagators),
which is more efficient. 'Dis' is a kind of poor man's way for Prolog
programs to do a little bit of pruning, but it is a dead end since it is
still in the Prolog style. If you really need nondeterminism (search)
in a strong way, you should use the constraint style and not the Prolog
style. If you need just a little bit of nondeterminism or if you are
just exploring solutions in a simple way, you can use Prolog style. But
Prolog style does not scale up to real problems.
Peter
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