% mmc -O2 --optimise-higher-order --optimise-constant-propagation --no-common-struct -C string2

:- module string2.
:- interface.

:- func string2.length(string::in) = (int::uo) is det.

:- func string2.foldr(func(character, T) = T, string, T) = T.
:- pred string2.foldr(pred(character, T, T), string, T, T).
:- mode string2.foldr(pred(in, in, out) is det, in, in, out) is det.

:- pred string2.foldr_substring(pred(character, T, T), string, int, int, T, T).
:- mode string2.foldr_substring(pred(in, in, out) is det, in, in, in,
    in, out) is det.

%-----------------------------------------------------------------------------%
%-----------------------------------------------------------------------------%

:- implementation.

:- import_module int.

%-----------------------------------------------------------------------------%

string2.foldr(F, String, Acc0) = Acc :-
    Closure = ( pred(X::in, Y::in, Z::out) is det :- Z = F(X, Y)),
    string2.foldr(Closure, String, Acc0, Acc).

string2.foldr(Closure, String, Acc0, Acc) :-
    string2.foldr_substring(Closure, String, 0, length(String), Acc0, Acc).

string2.foldr_substring(Closure, String, Start0, Count0, Acc0, Acc) :-
    Start = max2(0, Start0),
    Count = min2(Count0, length(String) - Start),
    string2.foldr_substring_2(Closure, String, Start, Count, Acc0, Acc).

:- pred string2.foldr_substring_2(pred(character, T, T), string, int, int, T, T).
:- mode string2.foldr_substring_2(pred(in, in, out) is det, in, in, in,
    in, out) is det.

string2.foldr_substring_2(Closure, String, I, Count, !Acc) :-
    ( 0 < Count ->
        Closure(string2.unsafe_index(String, I + Count - 1), !Acc),
        string2.foldr_substring_2(Closure, String, I, Count - 1, !Acc)
    ;
        true
    ).

:- func string2.unsafe_index(string, int) = character.

:- pragma foreign_proc("C",
    string2.unsafe_index(Str::in, Index::in) = (Ch::out),
    [will_not_call_mercury, promise_pure, thread_safe, will_not_modify_trail,
        does_not_affect_liveness],
"
    Ch = Str[Index];
").

:- pragma foreign_proc("C",
    string2.length(Str::in) = (Length::uo),
    [will_not_call_mercury, promise_pure, thread_safe, will_not_modify_trail,
        does_not_affect_liveness],
"
    Length = strlen(Str);
").

:- func max2(int, int) = int.

max2(X_4, Y_5) = Max_6 :-
    (if
      int.(X_4 > Y_5)
    then
      Max_6 = X_4
    else
      Max_6 = Y_5
    ).

:- func min2(int, int) = int.

min2(X_4, Y_5) = Min_6 :-
    (if
      int.(X_4 < Y_5)
    then
      Min_6 = X_4
    else
      Min_6 = Y_5
    ).