mercury/library/array.m

%-----------------------------------------------------------------------------%
% Copyright (C) 1993-1995, 1997-2001 The University of Melbourne.
% This file may only be copied under the terms of the GNU Library General
% Public License - see the file COPYING.LIB in the Mercury distribution.
%-----------------------------------------------------------------------------%

% File: array.m
% Main authors: fjh, bromage
% Stability: medium-low

% This module provides dynamically-sized one-dimensional arrays.
% Array indices start at zero.

% By default, the array__set and array__lookup procedures will check
% for bounds errors.  But for better performance, it is possible to
% disable some of the checking by compiling with `--intermodule-optimization'
% and with the C macro symbol `ML_OMIT_ARRAY_BOUNDS_CHECKS'
% defined, e.g. by using `MCFLAGS=--intermodule-optimization' and
% `CFLAGS=-DML_OMIT_ARRAY_BOUNDS_CHECKS' in your Mmakefile,
% or by compiling with the command
% `mmc --intermodule-optimization --cflags -DML_OMIT_ARRAY_BOUNDS_CHECKS'.
%
% For maximum performance, all bounds checking can be disabled by
% recompiling this module using `CFLAGS=-DML_OMIT_ARRAY_BOUNDS_CHECKS'
% or `mmc --cflags -DML_OMIT_ARRAY_BOUNDS_CHECKS' as above. You can
% either recompile the entire library, or just copy `array.m' to your
% application's source directory and link with it directly instead of as
% part of the library.
%

% WARNING!
%
% Arrays are currently not unique objects - until this situation is
% resolved it is up to the programmer to ensure that arrays are used
% in such a way as to preserve correctness.  In the absence of mode
% reordering, one should therefore assume that evaluation will take
% place in left-to-right order.  For example, the following code will
% probably not work as expected (f is a function, A an array, I an
% index, and X an appropriate value):
%
%       Y = f(A ^ elem(I) := X, A ^ elem(I))
%
% The compiler is likely to compile this as
%
%       V0 = A ^ elem(I) := X,
%       V1 = A ^ elem(I),
%       Y  = f(V0, V1)
%
% and will be unaware that the first line should be ordered
% *after* the second.  The safest thing to do is write things out
% by hand in the form
%
%       A0I = A0 ^ elem(I),
%       A1  = A0 ^ elem(I) := X,
%       Y   = f(A1, A0I)

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

:- module array.
:- interface.
:- import_module list, std_util, random.

:- type array(T).

:- inst array(I) = bound(array(I)).
:- inst array == array(ground).
:- inst array_skel == array(free).

	% XXX the current Mercury compiler doesn't support `ui' modes,
	% so to work-around that problem, we currently don't use
	% unique modes in this module.

% :- inst uniq_array(I) = unique(array(I)).
% :- inst uniq_array == uniq_array(unique).
:- inst uniq_array(I) = bound(array(I)). % XXX work-around
:- inst uniq_array == uniq_array(ground). % XXX work-around
:- inst uniq_array_skel == uniq_array(free).

:- mode array_di == di(uniq_array).
:- mode array_uo == out(uniq_array).
:- mode array_ui == in(uniq_array).

% :- inst mostly_uniq_array(I) = mostly_unique(array(I)).
% :- inst mostly_uniq_array == mostly_uniq_array(mostly_unique).
:- inst mostly_uniq_array(I) = bound(array(I)).	% XXX work-around
:- inst mostly_uniq_array == mostly_uniq_array(ground).	% XXX work-around
:- inst mostly_uniq_array_skel == mostly_uniq_array(free).

:- mode array_mdi == mdi(mostly_uniq_array).
:- mode array_muo == out(mostly_uniq_array).
:- mode array_mui == in(mostly_uniq_array).

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

	% array__make_empty_array(Array) creates an array of size zero
	% starting at lower bound 0.
:- pred array__make_empty_array(array(T)).
:- mode array__make_empty_array(array_uo) is det.

:- func array__make_empty_array = array(T).
:- mode array__make_empty_array = array_uo is det.

	% array__init(Size, Init, Array) creates an array
	% with bounds from 0 to Size-1, with each element initialized to Init.
:- pred array__init(int, T, array(T)).
:- mode array__init(in, in, array_uo) is det.

:- func array__init(int, T) = array(T).
:- mode array__init(in, in) = array_uo is det.

	% array/1 is a function that constructs an array from a list.
	% (It does the same thing as the predicate array__from_list/2.)
	% The syntax `array([...])' is used to represent arrays
	% for io__read, io__write, term_to_type, and type_to_term.
:- func array(list(T)) = array(T).
:- mode array(in) = array_uo is det.

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

	% array__min returns the lower bound of the array.
	% Note: in this implementation, the lower bound is always zero.
:- pred array__min(array(_T), int).
:- mode array__min(array_ui, out) is det.
:- mode array__min(in, out) is det.

:- func array__min(array(_T)) = int.
:- mode array__min(array_ui) = out is det.
:- mode array__min(in) = out is det.

	% array__max returns the upper bound of the array.
:- pred array__max(array(_T), int).
:- mode array__max(array_ui, out) is det.
:- mode array__max(in, out) is det.

:- func array__max(array(_T)) = int.
:- mode array__max(array_ui) = out is det.
:- mode array__max(in) = out is det.

	% array__size returns the length of the array,
	% i.e. upper bound - lower bound + 1.
:- pred array__size(array(_T), int).
:- mode array__size(array_ui, out) is det.
:- mode array__size(in, out) is det.

:- func array__size(array(_T)) = int.
:- mode array__size(array_ui) = out is det.
:- mode array__size(in) = out is det.

	% array__bounds returns the upper and lower bounds of an array.
	% Note: in this implementation, the lower bound is always zero.
:- pred array__bounds(array(_T), int, int).
:- mode array__bounds(array_ui, out, out) is det.
:- mode array__bounds(in, out, out) is det.

	% array__in_bounds checks whether an index is in the bounds
	% of an array.
:- pred array__in_bounds(array(_T), int).
:- mode array__in_bounds(array_ui, in) is semidet.
:- mode array__in_bounds(in, in) is semidet.

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

	% array__lookup returns the Nth element of an array.
	% It is an error if the index is out of bounds.
:- pred array__lookup(array(T), int, T).
:- mode array__lookup(array_ui, in, out) is det.
:- mode array__lookup(in, in, out) is det.

:- func array__lookup(array(T), int) = T.
:- mode array__lookup(array_ui, in) = out is det.
:- mode array__lookup(in, in) = out is det.

	% array__semidet_lookup returns the Nth element of an array.
	% It fails if the index is out of bounds.
:- pred array__semidet_lookup(array(T), int, T).
:- mode array__semidet_lookup(array_ui, in, out) is semidet.
:- mode array__semidet_lookup(in, in, out) is semidet.

	% array__set sets the nth element of an array, and returns the
	% resulting array (good opportunity for destructive update ;-).  
	% It is an error if the index is out of bounds.
:- pred array__set(array(T), int, T, array(T)).
:- mode array__set(array_di, in, in, array_uo) is det.

:- func array__set(array(T), int, T) = array(T).
:- mode array__set(array_di, in, in) = array_uo is det.

	% array__semidet_set sets the nth element of an array,
	% and returns the resulting array.
	% It fails if the index is out of bounds.
:- pred array__semidet_set(array(T), int, T, array(T)).
:- mode array__semidet_set(array_di, in, in, array_uo) is semidet.

	% array__slow_set sets the nth element of an array,
	% and returns the resulting array.  The initial array is not
	% required to be unique, so the implementation may not be able to use
	% destructive update.
	% It is an error if the index is out of bounds.
:- pred array__slow_set(array(T), int, T, array(T)).
:- mode array__slow_set(array_ui, in, in, array_uo) is det.
:- mode array__slow_set(in, in, in, array_uo) is det.

:- func array__slow_set(array(T), int, T) = array(T).
:- mode array__slow_set(array_ui, in, in) = array_uo is det.
:- mode array__slow_set(in, in, in) = array_uo is det.

	% array__semidet_slow_set sets the nth element of an array,
	% and returns the resulting array.  The initial array is not
	% required to be unique, so the implementation may not be able to use
	% destructive update.
	% It fails if the index is out of bounds.
:- pred array__semidet_slow_set(array(T), int, T, array(T)).
:- mode array__semidet_slow_set(array_ui, in, in, array_uo) is semidet.
:- mode array__semidet_slow_set(in, in, in, array_uo) is semidet.

	% Field selection for arrays.
	% Array ^ elem(Index) = array__lookup(Array, Index).
:- func array__elem(int, array(T)) = T.
:- mode array__elem(in, array_ui) = out is det.
:- mode array__elem(in, in) = out is det.

	% Field update for arrays.
	% (Array ^ elem(Index) := Value) = array__set(Array, Index, Value).
:- func 'array__elem :='(int, array(T), T) = array(T).
:- mode 'array__elem :='(in, array_ui, in) = array_uo is det.

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

	% array__copy(Array0, Array):
	% Makes a new unique copy of an array.
:- pred array__copy(array(T), array(T)).
:- mode array__copy(array_ui, array_uo) is det.
:- mode array__copy(in, array_uo) is det.

:- func array__copy(array(T)) = array(T).
:- mode array__copy(array_ui) = array_uo is det.
:- mode array__copy(in) = array_uo is det.

	% array__resize(Array0, Size, Init, Array):
	% The array is expanded or shrunk to make it fit
	% the new size `Size'.  Any new entries are filled
	% with `Init'.
:- pred array__resize(array(T), int, T, array(T)).
:- mode array__resize(array_di, in, in, array_uo) is det.

:- func array__resize(array(T), int, T) = array(T).
:- mode array__resize(array_di, in, in) = array_uo is det.

	% array__shrink(Array0, Size, Array):
	% The array is shrunk to make it fit the new size `Size'.
	% It is an error if `Size' is larger than the size of `Array0'.
:- pred array__shrink(array(T), int, array(T)).
:- mode array__shrink(array_di, in, array_uo) is det.

:- func array__shrink(array(T), int) = array(T).
:- mode array__shrink(array_di, in) = array_uo is det.

	% array__from_list takes a list,
	% and returns an array containing those elements in
	% the same order that they occured in the list.
:- pred array__from_list(list(T), array(T)).
:- mode array__from_list(in, array_uo) is det.

:- func array__from_list(list(T)) = array(T).
:- mode array__from_list(in) = array_uo is det.

	% array__to_list takes an array and returns a list containing
	% the elements of the array in the same order that they
	% occurred in the array.
:- pred array__to_list(array(T), list(T)).
:- mode array__to_list(array_ui, out) is det.
:- mode array__to_list(in, out) is det.

:- func array__to_list(array(T)) = list(T).
:- mode array__to_list(array_ui) = out is det.
:- mode array__to_list(in) = out is det.

	% array__fetch_items takes an array and a lower and upper
	% index, and places those items in the array between these
	% indices into a list.  It is an error if either index is
	% out of bounds.
:- pred array__fetch_items(array(T), int, int, list(T)).
:- mode array__fetch_items(in, in, in, out) is det.

:- func array__fetch_items(array(T), int, int) = list(T).
:- mode array__fetch_items(array_ui, in, in) = out is det.
:- mode array__fetch_items(in, in, in) = out is det.

	% array__bsearch takes an array, an element to be found
	% and a comparison predicate and returns the position of
	% the element in the array.  Assumes the array is in sorted
	% order.  Fails if the element is not present.  If the
	% element to be found appears multiple times, the index of
	% the first occurrence is returned.
:- pred array__bsearch(array(T), T, pred(T, T, comparison_result),
			maybe(int)).
:- mode array__bsearch(array_ui, in, pred(in, in, out) is det, out) is det.
:- mode array__bsearch(in, in, pred(in, in, out) is det, out) is det.

:- func array__bsearch(array(T), T, func(T,T) = comparison_result) = maybe(int).
:- mode array__bsearch(array_ui, in, func(in,in) = out is det) = out is det.
:- mode array__bsearch(in, in, func(in,in) = out is det) = out is det.

	% array__map(Closure, OldArray, NewArray) applys `Closure' to
	% each of the elements of `OldArray' to create `NewArray'.
:- pred array__map(pred(T1, T2), array(T1), array(T2)).
:- mode array__map(pred(in, out) is det, array_di, array_uo) is det.

:- func array__map(func(T1) = T2, array(T1)) = array(T2).
:- mode array__map(func(in) = out is det, array_di) = array_uo is det.

:- func array_compare(array(T), array(T)) = comparison_result.
:- mode array_compare(in, in) = out is det.

	% array__sort(Array) returns a version of Array sorted
	% into ascending order.
	%
	% This sort is not stable.  That is, elements that
	% compare/3 decides are equal will appear together in
	% the sorted array, but not necessarily in the same
	% order in which they occurred in the input array.
	% This is primarily only an issue with types with
	% user-defined equivalence for which `equivalent'
	% objects are otherwise distinguishable.
	%
:- func array__sort(array(T)) = array(T).
:- mode array__sort(array_di) = array_uo is det.

	% array__foldl(Fn, Array, X) is equivalent to
	% 	list__foldl(Fn, array__to_list(Array), X)
	% but more efficient.
	%
:- func array__foldl(func(T1, T2) = T2, array(T1), T2) = T2.
:- mode array__foldl(func(in, in) = out is det, array_ui, in) = out is det.
:- mode array__foldl(func(in, in) = out is det, in, in) = out is det.
:- mode array__foldl(func(in, di) = uo is det, array_ui, di) = uo is det.
:- mode array__foldl(func(in, di) = uo is det, in, di) = uo is det.

	% array__foldr(Fn, Array, X) is equivalent to
	% 	list__foldr(Fn, array__to_list(Array), X)
	% but more efficient.
	%
:- func array__foldr(func(T1, T2) = T2, array(T1), T2) = T2.
:- mode array__foldr(func(in, in) = out is det, array_ui, in) = out is det.
:- mode array__foldr(func(in, in) = out is det, in, in) = out is det.
:- mode array__foldr(func(in, di) = uo is det, array_ui, di) = uo is det.
:- mode array__foldr(func(in, di) = uo is det, in, di) = uo is det.

	% array__random_permutation(A0, A, RS0, RS) permutes the elements in
	% A0 given random seed RS0 and returns the permuted array in A
	% and the next random seed in RS.
	%
:- pred array__random_permutation(array(T), array(T),
		random__supply, random__supply).
:- mode array__random_permutation(array_di, array_uo, mdi, muo) is det.

%-----------------------------------------------------------------------------%
:- implementation.

% Everything beyond here is not intended as part of the public interface,
% and will not appear in the Mercury Library Reference Manual.

%-----------------------------------------------------------------------------%
:- interface.

	% The following predicates have to be declared in the interface,
	% otherwise dead code elimination will remove them.
	% But they're an implementation detail; user code should just
	% use the generic versions.

	% unify/2 for arrays

:- pred array_equal(array(T), array(T)).
:- mode array_equal(in, in) is semidet.

	% compare/3 for arrays

:- pred array_compare(comparison_result, array(T), array(T)).
:- mode array_compare(out, in, in) is det.

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

:- implementation.
:- import_module int.

/****
lower bounds other than zero are not supported
	% array__resize takes an array and new lower and upper bounds.
	% the array is expanded or shrunk at each end to make it fit
	% the new bounds.
:- pred array__resize(array(T), int, int, array(T)).
:- mode array__resize(in, in, in, out) is det.
****/

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

% Arrays are implemented using the C interface.

% The C type which defines the representation of arrays is
% MR_ArrayType; it is defined in runtime/mercury_library_types.h.

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

:- pragma foreign_decl("C", "
#ifdef MR_HIGHLEVEL_CODE
  bool MR_CALL mercury__array__do_unify__array_1_0(
  	MR_Mercury_Type_Info type_info, MR_Box x, MR_Box y);
  bool MR_CALL mercury__array____Unify____array_1_0(
	MR_Mercury_Type_Info type_info, MR_Array x, MR_Array y);
  void MR_CALL mercury__array__do_compare__array_1_0(MR_Mercury_Type_Info
 	 type_info, MR_Comparison_Result *result, MR_Box x, MR_Box y);
  void MR_CALL mercury__array____Compare____array_1_0(MR_Mercury_Type_Info
	type_info, MR_Comparison_Result *result, MR_Array x, MR_Array y);
#endif
").

:- pragma foreign_code("C", "

#ifdef MR_HIGHLEVEL_CODE

MR_define_type_ctor_info(array, array, 1, MR_TYPECTOR_REP_ARRAY);

/* forward decl, to suppress gcc -Wmissing-decl warning */
void sys_init_array_module_builtins(void);

/*
** This empty initialization function is needed just to
** match the one that we use for LLDS grades.
*/
void
sys_init_array_module_builtins(void)
{
	/* no initialization needed */
}

bool MR_CALL
mercury__array__do_unify__array_1_0(MR_Mercury_Type_Info type_info,
	MR_Box x, MR_Box y)
{
	return mercury__array____Unify____array_1_0(
		type_info, (MR_Array) x, (MR_Array) y);
}

bool MR_CALL
mercury__array____Unify____array_1_0(MR_Mercury_Type_Info type_info,
	MR_Array x, MR_Array y)
{
	return mercury__array__array_equal_2_p_0(type_info, x, y);
}

void MR_CALL
mercury__array__do_compare__array_1_0(
	MR_Mercury_Type_Info type_info, MR_Comparison_Result *result,
	MR_Box x, MR_Box y)
{
	mercury__array____Compare____array_1_0(
		type_info, result, (MR_Array) x, (MR_Array) y);
}

void MR_CALL
mercury__array____Compare____array_1_0(
	MR_Mercury_Type_Info type_info, MR_Comparison_Result *result,
	MR_Array x, MR_Array y)
{
	mercury__array__array_compare_3_p_0(type_info, result, x, y);
}

#else

MR_DEFINE_BUILTIN_TYPE_CTOR_INFO(array, array, 1, MR_TYPECTOR_REP_ARRAY);

MR_declare_entry(mercury__array__array_equal_2_0);
MR_declare_entry(mercury__array__array_compare_3_0);

MR_BEGIN_MODULE(array_module_builtins)
	MR_init_entry(mercury____Unify___array__array_1_0);
	MR_init_entry(mercury____Compare___array__array_1_0);
MR_BEGIN_CODE

MR_define_entry(mercury____Unify___array__array_1_0);
	/* this is implemented in Mercury, not hand-coded low-level C */
	MR_tailcall(MR_ENTRY(mercury__array__array_equal_2_0),
		MR_ENTRY(mercury____Unify___array__array_1_0));

MR_define_entry(mercury____Compare___array__array_1_0);
	/* this is implemented in Mercury, not hand-coded low-level C */
	MR_tailcall(MR_ENTRY(mercury__array__array_compare_3_0),
		MR_ENTRY(mercury____Compare___array__array_1_0));

MR_END_MODULE

/* Ensure that the initialization code for the above module gets run. */
/*
INIT sys_init_array_module_builtins
*/

MR_MODULE_STATIC_OR_EXTERN MR_ModuleFunc array_module_builtins;

void sys_init_array_module_builtins(void);
		/* suppress gcc -Wmissing-decl warning */
void sys_init_array_module_builtins(void) {
	array_module_builtins();
	MR_INIT_TYPE_CTOR_INFO(
		mercury_data_array__type_ctor_info_array_1,
		array__array_1_0);
	MR_register_type_ctor_info(
		&mercury_data_array__type_ctor_info_array_1);
}

#endif /* ! MR_HIGHLEVEL_CODE */

").

:- pragma foreign_code("MC++", "
    MR_DEFINE_BUILTIN_TYPE_CTOR_INFO(array, array, 1, MR_TYPECTOR_REP_ARRAY)

    static int
    __Unify____array_1_0(MR_Word type_info, 
		MR_Word x, MR_Word y)
    {
            mercury::runtime::Errors::SORRY(""unify for array"");
            return 0;
    }

    static void
    __Compare____array_1_0(
            MR_Word type_info, MR_Word_Ref result, MR_Word x, MR_Word y)
    {
            mercury::runtime::Errors::SORRY(""compare for array"");
    }

    static int
    do_unify__array_1_0(MR_Word type_info, MR_Box x, MR_Box y)
    {
            return mercury::array__c_code::mercury_code::__Unify____array_1_0(
                    type_info, 
                    dynamic_cast<MR_Array>(x),
                    dynamic_cast<MR_Array>(y));
    }

    static void
    do_compare__array_1_0(
            MR_Word type_info, MR_Word_Ref result, MR_Box x, MR_Box y)
    {
            mercury::array__c_code::mercury_code::__Compare____array_1_0(
                    type_info, result, 
                    dynamic_cast<MR_Array>(x),
                    dynamic_cast<MR_Array>(y));
    }
").


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

	% unify/2 for arrays

array_equal(Array1, Array2) :-
	array__size(Array1, Size),
	array__size(Array2, Size),
	array__equal_elements(0, Size, Array1, Array2).

:- pred array__equal_elements(int, int, array(T), array(T)).
:- mode array__equal_elements(in, in, in, in) is semidet.

array__equal_elements(N, Size, Array1, Array2) :-
	( N = Size ->
		true
	;
		array__lookup(Array1, N, Elem),
		array__lookup(Array2, N, Elem),
		N1 is N + 1,
		array__equal_elements(N1, Size, Array1, Array2)
	).

	% compare/3 for arrays

array_compare(Result, Array1, Array2) :-
	array__size(Array1, Size1),
	array__size(Array2, Size2),
	compare(SizeResult, Size1, Size2),
	( SizeResult = (=) ->
		array__compare_elements(0, Size1, Array1, Array2, Result)
	;
		Result = SizeResult
	).

:- pred array__compare_elements(int, int, array(T), array(T),
			comparison_result).
:- mode array__compare_elements(in, in, in, in, out) is det.

array__compare_elements(N, Size, Array1, Array2, Result) :-
	( N = Size ->
		Result = (=)
	;
		array__lookup(Array1, N, Elem1),
		array__lookup(Array2, N, Elem2),
		compare(ElemResult, Elem1, Elem2),
		( ElemResult = (=) ->
			N1 is N + 1,
			array__compare_elements(N1, Size, Array1, Array2,
				Result)
		;
			Result = ElemResult
		)
	).

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

:- pragma foreign_decl("C", "
#include ""mercury_heap.h""		/* for MR_maybe_record_allocation() */
#include ""mercury_library_types.h""	/* for MR_ArrayType */
#include ""mercury_misc.h""		/* for MR_fatal_error() */
").

:- pragma foreign_decl("C", "
MR_ArrayType *ML_make_array(MR_Integer size, MR_Word item);
").

:- pragma foreign_code("C", "
MR_ArrayType *
ML_make_array(MR_Integer size, MR_Word item)
{
	MR_Integer i;
	MR_ArrayType *array;

	array = MR_make_array(size);
	array->size = size;
	for (i = 0; i < size; i++) {
		array->elements[i] = item;
	}
	return array;
}
").

:- pragma foreign_proc("C", 
		array__init(Size::in, Item::in, Array::array_uo),
		[will_not_call_mercury, thread_safe], "
	MR_maybe_record_allocation(Size + 1, MR_PROC_LABEL, ""array:array/1"");
	Array = (MR_Word) ML_make_array(Size, Item);
").

:- pragma foreign_proc("C",
		array__make_empty_array(Array::array_uo),
		[will_not_call_mercury, thread_safe], "
	MR_maybe_record_allocation(1, MR_PROC_LABEL, ""array:array/1"");
	Array = (MR_Word) ML_make_array(0, 0);
").

:- pragma foreign_proc("MC++", 
		array__init(Size::in, Item::in, Array::array_uo),
		[will_not_call_mercury, thread_safe], "
        mercury::runtime::Errors::SORRY(""foreign code for this predicate"");
		// XXX still need to do init
	Array = (MR_Word) System::Array::CreateInstance(Item->GetType(), Size);
").

:- pragma foreign_proc("MC++",
		array__make_empty_array(Array::array_uo),
		[will_not_call_mercury, thread_safe], "
        mercury::runtime::Errors::SORRY(""foreign code for this predicate"");
		// XXX this is inefficient.
	Array = (MR_Word) 
		System::Array::CreateInstance(
			(new System::Object)->GetType(), 0);
").


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

:- pragma foreign_proc("C",
		array__min(Array::array_ui, Min::out),
		[will_not_call_mercury, thread_safe], "
	/* Array not used */
	Min = 0;
").
:- pragma foreign_proc("C", 
		array__min(Array::in, Min::out),
		[will_not_call_mercury, thread_safe], "
	/* Array not used */
	Min = 0;
").

:- pragma foreign_proc("MC++",
		array__min(Array::array_ui, Min::out),
		[will_not_call_mercury, thread_safe], "
        mercury::runtime::Errors::SORRY(""foreign code for this predicate"");
	/* Array not used */
	Min = 0;
").
:- pragma foreign_proc("MC++", 
		array__min(Array::in, Min::out),
		[will_not_call_mercury, thread_safe], "
        mercury::runtime::Errors::SORRY(""foreign code for this predicate"");
	/* Array not used */
	Min = 0;
").

:- pragma foreign_proc("C", 
		array__max(Array::array_ui, Max::out), 
		[will_not_call_mercury, thread_safe], "
	Max = ((MR_ArrayType *)Array)->size - 1;
").
:- pragma foreign_proc("C",
		array__max(Array::in, Max::out), 
		[will_not_call_mercury, thread_safe], "
	Max = ((MR_ArrayType *)Array)->size - 1;
").
:- pragma foreign_proc("MC++", 
		array__max(Array::array_ui, Max::out), 
		[will_not_call_mercury, thread_safe], "
        mercury::runtime::Errors::SORRY(""foreign code for this predicate"");
	Max = Array->get_Length() - 1;
").
:- pragma foreign_proc("MC++",
		array__max(Array::in, Max::out), 
		[will_not_call_mercury, thread_safe], "
        mercury::runtime::Errors::SORRY(""foreign code for this predicate"");
	Max = Array->get_Length() - 1;
").


array__bounds(Array, Min, Max) :-
	array__min(Array, Min),
	array__max(Array, Max).

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

:- pragma foreign_proc("C",
		array__size(Array::array_ui, Max::out),
		[will_not_call_mercury, thread_safe], "
	Max = ((MR_ArrayType *)Array)->size;
").
:- pragma foreign_proc("C",
		array__size(Array::in, Max::out),
		[will_not_call_mercury, thread_safe], "
	Max = ((MR_ArrayType *)Array)->size;
").

:- pragma foreign_proc("MC++",
		array__size(Array::array_ui, Max::out),
		[will_not_call_mercury, thread_safe], "
        mercury::runtime::Errors::SORRY(""foreign code for this predicate"");
	Max = Array->get_Length() - 1;
").
:- pragma foreign_proc("MC++",
		array__size(Array::in, Max::out),
		[will_not_call_mercury, thread_safe], "
        mercury::runtime::Errors::SORRY(""foreign code for this predicate"");
	Max = Array->get_Length() - 1;
").


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

array__in_bounds(Array, Index) :-
	array__bounds(Array, Min, Max),
	Min =< Index, Index =< Max.

array__semidet_lookup(Array, Index, Item) :-
	array__in_bounds(Array, Index),
	array__lookup(Array, Index, Item).

array__semidet_set(Array0, Index, Item, Array) :-
	array__in_bounds(Array0, Index),
	array__set(Array0, Index, Item, Array).

array__semidet_slow_set(Array0, Index, Item, Array) :-
	array__in_bounds(Array0, Index),
	array__slow_set(Array0, Index, Item, Array).

array__slow_set(Array0, Index, Item, Array) :-
	array__copy(Array0, Array1),
	array__set(Array1, Index, Item, Array).

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

:- pragma foreign_proc("C",
		array__lookup(Array::array_ui, Index::in, Item::out),
		[will_not_call_mercury, thread_safe], "{
	MR_ArrayType *array = (MR_ArrayType *)Array;
#ifndef ML_OMIT_ARRAY_BOUNDS_CHECKS
	if ((MR_Unsigned) Index >= (MR_Unsigned) array->size) {
		MR_fatal_error(""array__lookup: array index out of bounds"");
	}
#endif
	Item = array->elements[Index];
}").
:- pragma foreign_proc("C",
		array__lookup(Array::in, Index::in, Item::out),
		[will_not_call_mercury, thread_safe], "{
	MR_ArrayType *array = (MR_ArrayType *)Array;
#ifndef ML_OMIT_ARRAY_BOUNDS_CHECKS
	if ((MR_Unsigned) Index >= (MR_Unsigned) array->size) {
		MR_fatal_error(""array__lookup: array index out of bounds"");
	}
#endif
	Item = array->elements[Index];
}").

:- pragma foreign_proc("MC++",
		array__lookup(Array::array_ui, Index::in, Item::out),
		[will_not_call_mercury, thread_safe], "{
        mercury::runtime::Errors::SORRY(""foreign code for this predicate"");
	Item = dynamic_cast<MR_Word>(Array->GetValue(Index));
}").
:- pragma foreign_proc("MC++",
		array__lookup(Array::in, Index::in, Item::out),
		[will_not_call_mercury, thread_safe], "{
        mercury::runtime::Errors::SORRY(""foreign code for this predicate"");
	Item = dynamic_cast<MR_Word>(Array->GetValue(Index));
}").


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

:- pragma foreign_proc("C",
		array__set(Array0::array_di, Index::in,
		Item::in, Array::array_uo),
		[will_not_call_mercury, thread_safe], "{
	MR_ArrayType *array = (MR_ArrayType *)Array0;
#ifndef ML_OMIT_ARRAY_BOUNDS_CHECKS
	if ((MR_Unsigned) Index >= (MR_Unsigned) array->size) {
		MR_fatal_error(""array__set: array index out of bounds"");
	}
#endif
	array->elements[Index] = Item;	/* destructive update! */
	Array = Array0;
}").

:- pragma foreign_proc("MC++",
		array__set(Array0::array_di, Index::in,
		Item::in, Array::array_uo),
		[will_not_call_mercury, thread_safe], "{
	Array0->SetValue(Item, Index);	/* destructive update! */
	Array = Array0;
        mercury::runtime::Errors::SORRY(""foreign code for this predicate"");
}").


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

:- pragma foreign_decl("C", "
MR_ArrayType * ML_resize_array(MR_ArrayType *old_array,
					MR_Integer array_size, MR_Word item);
").

:- pragma foreign_code("C", "
MR_ArrayType *
ML_resize_array(MR_ArrayType *old_array, MR_Integer array_size,
				MR_Word item)
{
	MR_Integer i;
	MR_ArrayType* array;
	MR_Integer elements_to_copy;

	elements_to_copy = old_array->size;
	if (elements_to_copy == array_size) return old_array;
	if (elements_to_copy > array_size) {
		elements_to_copy = array_size;
	}

	array = (MR_ArrayType *) MR_GC_NEW_ARRAY(MR_Word, array_size + 1);
	array->size = array_size;
	for (i = 0; i < elements_to_copy; i++) {
		array->elements[i] = old_array->elements[i];
	}
	for (; i < array_size; i++) {
		array->elements[i] = item;
	}

	/*
	** since the mode on the old array is `array_di', it is safe to
	** deallocate the storage for it
	*/
	MR_GC_free(old_array);

	return array;
}
").

:- pragma foreign_proc("C",
		array__resize(Array0::array_di, Size::in, Item::in,
		Array::array_uo), [will_not_call_mercury, thread_safe], "
	MR_maybe_record_allocation(Size + 1, MR_PROC_LABEL, ""array:array/1"");
	Array = (MR_Word) ML_resize_array(
				(MR_ArrayType *) Array0, Size, Item);
").
:- pragma foreign_proc("MC++",
		array__resize(_Array0::array_di, _Size::in, _Item::in,
		_Array::array_uo), [will_not_call_mercury, thread_safe], "
	mercury::runtime::Errors::SORRY(""foreign code for this function"");
").


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

:- pragma foreign_decl("C", "
MR_ArrayType * ML_shrink_array(MR_ArrayType *old_array,
					MR_Integer array_size);
").

:- pragma foreign_code("C", "
MR_ArrayType *
ML_shrink_array(MR_ArrayType *old_array, MR_Integer array_size)
{
	MR_Integer i;
	MR_ArrayType* array;
	MR_Integer old_array_size;

	old_array_size = old_array->size;
	if (old_array_size == array_size) return old_array;
	if (old_array_size < array_size) {
		MR_fatal_error(
			""array__shrink: can't shrink to a larger size"");
	}

	array = (MR_ArrayType *) MR_GC_NEW_ARRAY(MR_Word, array_size + 1);
	array->size = array_size;
	for (i = 0; i < array_size; i++) {
		array->elements[i] = old_array->elements[i];
	}

	/*
	** since the mode on the old array is `array_di', it is safe to
	** deallocate the storage for it
	*/
	MR_GC_free(old_array);

	return array;
}
").

:- pragma foreign_proc("C",
		array__shrink(Array0::array_di, Size::in, Array::array_uo),
		[will_not_call_mercury, thread_safe], "
	MR_maybe_record_allocation(Size + 1, MR_PROC_LABEL, ""array:array/1"");
	Array = (MR_Word) ML_shrink_array(
				(MR_ArrayType *) Array0, Size);
").
:- pragma foreign_proc("MC++",
		array__shrink(_Array0::array_di, _Size::in, _Array::array_uo),
		[will_not_call_mercury, thread_safe], "
	mercury::runtime::Errors::SORRY(""foreign code for this function"");
").


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

:- pragma foreign_decl("C", "
MR_ArrayType *ML_copy_array(MR_ArrayType *old_array);
").

:- pragma foreign_code("C", "
MR_ArrayType *
ML_copy_array(MR_ArrayType *old_array)
{
	/*
	** Any changes to this function will probably also require
	** changes to deepcopy() in runtime/deep_copy.c.
	*/

	MR_Integer i;
	MR_ArrayType* array;
	MR_Integer array_size;

	array_size = old_array->size;
	array = MR_make_array(array_size);
	array->size = array_size;
	for (i = 0; i < array_size; i++) {
		array->elements[i] = old_array->elements[i];
	}
	return array;
}
").

:- pragma foreign_proc("C",
		array__copy(Array0::array_ui, Array::array_uo),
		[will_not_call_mercury, thread_safe], "
	MR_maybe_record_allocation((((MR_ArrayType *) Array0)->size) + 1,
		MR_PROC_LABEL, ""array:array/1"");
	Array = (MR_Word) ML_copy_array((MR_ArrayType *) Array0);
").

:- pragma foreign_proc("C",
		array__copy(Array0::in, Array::array_uo),
		[will_not_call_mercury, thread_safe], "
	MR_maybe_record_allocation((((MR_ArrayType *) Array0)->size) + 1,
		MR_PROC_LABEL, ""array:array/1"");
	Array = (MR_Word) ML_copy_array((MR_ArrayType *) Array0);
").

:- pragma foreign_proc("MC++",
		array__copy(Array0::array_ui, Array::array_uo),
		[will_not_call_mercury, thread_safe], "
		// XXX need to deep copy it
	mercury::runtime::Errors::SORRY(""foreign code for this function"");
	Array = Array0;

").

:- pragma foreign_proc("MC++",
		array__copy(Array0::in, Array::array_uo),
		[will_not_call_mercury, thread_safe], "
	mercury::runtime::Errors::SORRY(""foreign code for this function"");
		// XXX need to deep copy it
	Array = Array0;
").

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

array(List) = Array :-
	array__from_list(List, Array).

array__from_list([], Array) :-
	array__make_empty_array(Array).
array__from_list(List, Array) :-
        List = [ Head | Tail ],
        list__length(List, Len),
        array__init(Len, Head, Array0),
        array__insert_items(Tail, 1, Array0, Array).

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

:- pred array__insert_items(list(T), int, array(T), array(T)).
:- mode array__insert_items(in, in, array_di, array_uo) is det.

array__insert_items([], _N, Array, Array).
array__insert_items([Head|Tail], N, Array0, Array) :-
        array__set(Array0, N, Head, Array1),
        N1 is N + 1,
        array__insert_items(Tail, N1, Array1, Array).

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

array__to_list(Array, List) :-
        array__bounds(Array, Low, High),
        array__fetch_items(Array, Low, High, List).

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

array__fetch_items(Array, Low, High, List) :-
	List = foldr_0(func(X, Xs) = [X | Xs], Array, [], Low, High).

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

array__bsearch(A, El, Compare, Result) :-
	array__bounds(A, Lo, Hi),
	array__bsearch_2(A, Lo, Hi, El, Compare, Result).

:- pred array__bsearch_2(array(T), int, int, T,
			pred(T, T, comparison_result), maybe(int)).
:- mode array__bsearch_2(in, in, in, in, pred(in, in, out) is det,
				out) is det.
array__bsearch_2(Array, Lo, Hi, El, Compare, Result) :-
	Width is Hi - Lo,

	% If Width < 0, there is no range left.
	( Width < 0 ->
	    Result = no
	;
	    % If Width == 0, we may just have found our element.
	    % Do a Compare to check.
	    ( Width = 0 ->
	        array__lookup(Array, Lo, X),
	        ( call(Compare, El, X, (=)) ->
		    Result = yes(Lo)
	        ;
		    Result = no
	        )
	    ;
	        % Otherwise find the middle element of the range
	        % and check against that.
	        Mid is (Lo + Hi) >> 1,	% `>> 1' is hand-optimized `div 2'.
	        array__lookup(Array, Mid, XMid),
	        call(Compare, XMid, El, Comp),
	        ( Comp = (<),
		    Mid1 is Mid + 1,
		    array__bsearch_2(Array, Mid1, Hi, El, Compare, Result)
	        ; Comp = (=),
		    array__bsearch_2(Array, Lo, Mid, El, Compare, Result)
	        ; Comp = (>),
		    Mid1 is Mid - 1,
		    array__bsearch_2(Array, Lo, Mid1, El, Compare, Result)
	        )
	    )
	).

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

array__map(Closure, OldArray, NewArray) :-
	( array__semidet_lookup(OldArray, 0, Elem0) ->
		array__size(OldArray, Size),
		call(Closure, Elem0, Elem),
		array__init(Size, Elem, NewArray0),
		array__map_2(1, Size, Closure, OldArray,
		NewArray0, NewArray)
	;
		array__make_empty_array(NewArray)
	).

:- pred array__map_2(int, int, pred(T1, T2), array(T1), array(T2), array(T2)).
:- mode array__map_2(in, in, pred(in, out) is det, in, array_di, array_uo)
		is det.

array__map_2(N, Size, Closure, OldArray, NewArray0, NewArray) :-
	( N >= Size ->
		NewArray = NewArray0
	;
		array__lookup(OldArray, N, OldElem),
		Closure(OldElem, NewElem),
		array__set(NewArray0, N, NewElem, NewArray1),
		array__map_2(N + 1, Size, Closure, OldArray,
		NewArray1, NewArray)
	).

%-----------------------------------------------------------------------------%
%-----------------------------------------------------------------------------%
% Ralph Becket <rwab1@cam.sri.com> 24/04/99
%	Function forms added.

array__make_empty_array = A :-
	array__make_empty_array(A).

array__init(N, X) = A :-
	array__init(N, X, A).

array__min(A) = N :-
	array__min(A, N).

array__max(A) = N :-
	array__max(A, N).

array__size(A) = N :-
	array__size(A, N).

array__lookup(A, N) = X :-
	array__lookup(A, N, X).

array__set(A1, N, X) = A2 :-
	array__set(A1, N, X, A2).

array__slow_set(A1, N, X) = A2 :-
	array__slow_set(A1, N, X, A2).

array__copy(A1) = A2 :-
	array__copy(A1, A2).

array__resize(A1, N, X) = A2 :-
	array__resize(A1, N, X, A2).

array__shrink(A1, N) = A2 :-
	array__shrink(A1, N, A2).

array__from_list(Xs) = A :-
	array__from_list(Xs, A).

array__to_list(A) = Xs :-
	array__to_list(A, Xs).

array__fetch_items(A, N1, N2) = Xs :-
	array__fetch_items(A, N1, N2, Xs).

array__bsearch(A, X, F) = MN :-
	P = ( pred(X1::in, X2::in, C::out) is det :- C = F(X1, X2) ),
	array__bsearch(A, X, P, MN).

array__map(F, A1) = A2 :-
	P = ( pred(X::in, Y::out) is det :- Y = F(X) ),
	array__map(P, A1, A2).

array_compare(A1, A2) = C :-
	array_compare(C, A1, A2).

array__elem(Index, Array) = array__lookup(Array, Index).

'array__elem :='(Index, Array, Value) = array__set(Array, Index, Value).

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

    % array__sort/1 has type specialised versions for arrays of
    % ints and strings on the expectation that these constitute
    % the common case and are hence worth providing a fast-path.
    %
    % Experiments indicate that type specialisation improves
    % array__sort/1 by a factor of 30-40%.
    %
:- pragma type_spec(array__sort/1, T = int).
:- pragma type_spec(array__sort/1, T = string).

array__sort(A) = samsort_subarray(A, array__min(A), array__max(A)).

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

array__random_permutation(A0, A, RS0, RS) :-
	Lo = array__min(A0),
	Hi = array__max(A0),
	Sz = array__size(A0),
	permutation_2(Lo, Lo, Hi, Sz, A0, A, RS0, RS).



:- pred permutation_2(int, int, int, int, array(T), array(T),
		random__supply, random__supply).
:- mode permutation_2(in, in, in, in, array_di, array_uo, mdi, muo) is det.

permutation_2(I, Lo, Hi, Sz, A0, A, RS0, RS) :-
	( if I > Hi then
		A  = A0,
		RS = RS0
	  else
	  	random__random(R, RS0, RS1),
	  	J  = Lo + (R `rem` Sz),
		A1 = swap_elems(A0, I, J),
		permutation_2(I + 1, Lo, Hi, Sz, A1, A, RS1, RS)
	).

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

:- func swap_elems(array(T), int, int) = array(T).
:- mode swap_elems(array_di, in, in) = array_uo is det.

swap_elems(A0, I, J) = A :-
	XI = A0 ^ elem(I),
	XJ = A0 ^ elem(J),
	A  = ((A0 ^ elem(I) := XJ)
		  ^ elem(J) := XI).

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

array__foldl(Fn, A, X) =
	foldl_0(Fn, A, X, array__min(A), array__max(A)).



:- func foldl_0(func(T1, T2) = T2, array(T1), T2, int, int) = T2.
:- mode foldl_0(func(in, in) = out is det, array_ui, in, in, in) = out is det.
:- mode foldl_0(func(in, in) = out is det, in, in, in, in) = out is det.
:- mode foldl_0(func(in, di) = uo is det, array_ui, di, in, in) = uo is det.
:- mode foldl_0(func(in, di) = uo is det, in, di, in, in) = uo is det.

foldl_0(Fn, A, X, I, Max) =
	( if Max < I	then X
			else foldl_0(Fn, A, Fn(A ^ elem(I), X), I + 1, Max)
	).

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

array__foldr(Fn, A, X) =
	foldr_0(Fn, A, X, array__min(A), array__max(A)).



:- func foldr_0(func(T1, T2) = T2, array(T1), T2, int, int) = T2.
:- mode foldr_0(func(in, in) = out is det, array_ui, in, in, in) = out is det.
:- mode foldr_0(func(in, in) = out is det, in, in, in, in) = out is det.
:- mode foldr_0(func(in, di) = uo is det, array_ui, di, in, in) = uo is det.
:- mode foldr_0(func(in, di) = uo is det, in, di, in, in) = uo is det.

foldr_0(Fn, A, X, Min, I) =
	( if I < Min	then X
			else foldr_0(Fn, A, Fn(A ^ elem(I), X), Min, I - 1)
	).

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

    % SAMsort (smooth applicative merge) invented by R.A. O'Keefe.
    %
    % SAMsort is a mergesort variant that works by identifying contiguous
    % monotonic sequences and merging them, thereby taking advantage of
    % any existing order in the input sequence.
    %
:- func samsort_subarray(array(T), int, int) = array(T).
:- mode samsort_subarray(array_di, in, in) = array_uo is det.

:- pragma type_spec(samsort_subarray/3, T = int).
:- pragma type_spec(samsort_subarray/3, T = string).

samsort_subarray(A0, Lo, Hi) = A :-
    samsort_up(0, A0, _, array__copy(A0), A, Lo, Hi, Lo).



:- pred samsort_up(int, array(T), array(T), array(T), array(T), int, int, int).
:- mode samsort_up(in, array_di, array_uo, array_di, array_uo, in, in, in)
            is det.

:- pragma type_spec(samsort_up/8, T = int).
:- pragma type_spec(samsort_up/8, T = string).

    % Precondition:
    %   We are N levels from the bottom (leaf nodes) of the tree.
    %   A0 is sorted from Lo .. I - 1.
    %   A0 and B0 are identical from I .. Hi.
    % Postcondition:
    %   B is sorted from Lo .. Hi.
    %
samsort_up(N, A0, A, B0, B, Lo, Hi, I) :-

    ( if I > Hi then

        A = A0,
        B = B0

      else if N > 0 then

        samsort_down(N - 1, B0, B1, A0, A1, I, Hi, J),

            % A1 is sorted from I .. J - 1.
            % A1 and B1 are identical from J .. Hi.

        B2 = merge_subarrays(A1, B1, Lo, I - 1, I, J - 1, Lo),
        A2 = A1,

            % B2 is sorted from Lo .. J - 1.

        samsort_up(N + 1, B2, B, A2, A, Lo, Hi, J)

      else /* N = 0, I = Lo */

        copy_run_ascending(A0, B0, B1, Lo, Hi, J),

            % B1 is sorted from Lo .. J - 1.

        samsort_up(N + 1, B1, B, A0, A, Lo, Hi, J)
    ).



:- pred samsort_down(int,array(T),array(T),array(T),array(T),int,int,int).
:- mode samsort_down(in, array_di, array_uo, array_di, array_uo, in, in, out)
            is det.

:- pragma type_spec(samsort_down/8, T = int).
:- pragma type_spec(samsort_down/8, T = string).

    % Precondition:
    %   We are N levels from the bottom (leaf nodes) of the tree.
    %   A0 and B0 are identical from Lo .. Hi.
    % Postcondition:
    %   B is sorted from Lo .. I - 1.
    %   A and B are identical from I .. Hi.
    %
samsort_down(N, A0, A, B0, B, Lo, Hi, I) :-

    ( if Lo > Hi then

        A = A0,
        B = B0,
        I = Lo

      else if N > 0 then

        samsort_down(N - 1, B0, B1, A0, A1, Lo, Hi, J),
        samsort_down(N - 1, B1, B2, A1, A2, J,  Hi, I),

            % A2 is sorted from Lo .. J - 1.
            % A2 is sorted from J  .. I - 1.

        A = A2,
        B = merge_subarrays(A2, B2, Lo, J - 1, J, I - 1, Lo)

            % B is sorted from Lo .. I - 1.

      else

        A = A0,
        copy_run_ascending(A0, B0, B, Lo, Hi, I)

            % B is sorted from Lo .. I - 1.
    ).

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

:- pred copy_run_ascending(array(T), array(T), array(T), int, int, int).
:- mode copy_run_ascending(array_ui, array_di, array_uo, in, in, out) is det.

:- pragma type_spec(copy_run_ascending/6, T = int).
:- pragma type_spec(copy_run_ascending/6, T = string).

copy_run_ascending(A, B0, B, Lo, Hi, I) :-
    ( if Lo < Hi, compare((>), A ^ elem(Lo), A ^ elem(Lo + 1)) then
        I = search_until((<), A, Lo, Hi),
        B = copy_subarray_reverse(A, B0, Lo, I - 1, I - 1)
      else
        I = search_until((>), A, Lo, Hi),
        B = copy_subarray(A, B0, Lo, I - 1, Lo)
    ).

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

:- func search_until(comparison_result, array(T), int, int) = int.
:- mode search_until(in, array_ui, in, in) = out is det.

:- pragma type_spec(search_until/4, T = int).
:- pragma type_spec(search_until/4, T = string).

search_until(R, A, Lo, Hi) =
    ( if Lo < Hi, not compare(R, A ^ elem(Lo), A ^ elem(Lo + 1))
      then search_until(R, A, Lo + 1, Hi)
      else Lo + 1
    ).

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

:- func copy_subarray(array(T), array(T), int, int, int) = array(T).
:- mode copy_subarray(array_ui, array_di, in, in, in) = array_uo is det.

:- pragma type_spec(copy_subarray/5, T = int).
:- pragma type_spec(copy_subarray/5, T = string).

copy_subarray(A, B, Lo, Hi, I) =
    ( if Lo =< Hi
      then copy_subarray(A, B ^ elem(I) := A ^ elem(Lo), Lo + 1, Hi, I + 1)
      else B
    ).

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

:- func copy_subarray_reverse(array(T), array(T), int, int, int) = array(T).
:- mode copy_subarray_reverse(array_ui, array_di, in, in, in) = array_uo is det.

:- pragma type_spec(copy_subarray_reverse/5, T = int).
:- pragma type_spec(copy_subarray_reverse/5, T = string).

copy_subarray_reverse(A, B, Lo, Hi, I) =
    ( if Lo =< Hi
      then copy_subarray_reverse(A, B ^ elem(I) := A ^ elem(Lo), Lo+1, Hi, I-1)
      else B
    ).

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

    % merges the two sorted consecutive subarrays Lo1 .. Hi1 and
    % Lo2 .. Hi2 from A into the subarray starting at I in B.
    % 
:- func merge_subarrays(array(T), array(T), int, int, int, int, int) = array(T).
:- mode merge_subarrays(array_ui, array_di, in, in, in, in, in) = array_uo
            is det.

:- pragma type_spec(merge_subarrays/7, T = int).
:- pragma type_spec(merge_subarrays/7, T = string).

merge_subarrays(A, B0, Lo1, Hi1, Lo2, Hi2, I) = B :-
    (      if Lo1 > Hi1 then B = copy_subarray(A, B0, Lo2, Hi2, I)
      else if Lo2 > Hi2 then B = copy_subarray(A, B0, Lo1, Hi1, I)
      else
        X1 = A ^ elem(Lo1),
        X2 = A ^ elem(Lo2),
        compare(R, X1, X2),
        (
            R = (<),
            B = merge_subarrays(A, B0^elem(I) := X1, Lo1+1, Hi1, Lo2, Hi2, I+1)
        ;
            R = (=),
            B = merge_subarrays(A, B0^elem(I) := X1, Lo1+1, Hi1, Lo2, Hi2, I+1)
        ;
            R = (>),
            B = merge_subarrays(A, B0^elem(I) := X2, Lo1, Hi1, Lo2+1, Hi2, I+1)
        )
    ).

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