%-----------------------------------------------------------------------------%
% Copyright (C) 1995 University of Melbourne.
% This file may only be copied under the terms of the GNU General
% Public License - see the file COPYING in the Mercury distribution.
%-----------------------------------------------------------------------------%
%
% Main authors: conway, fjh.
%
% This file provides a 'tree' data type.
% The code generater uses this to build a tree of instructions and
% then flatten them into a list.
%
%-----------------------------------------------------------------------------%
%-----------------------------------------------------------------------------%

:- module tree.
:- import_module list.

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

:- interface.
:- type tree(T)		--->	empty
			;	node(T)
			;	tree(tree(T), tree(T)).

:- pred tree__flatten(tree(T), list(T)).
:- mode tree__flatten(in, out) is det.

:- pred tree__is_empty(tree(T)).
:- mode tree__is_empty(in) is semidet.

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

:- implementation.

tree__flatten(T, L) :-
	tree__flatten_2(T, [], L).

:- pred tree__flatten_2(tree(T), list(T), list(T)).
:- mode tree__flatten_2(in, in, out) is det.
	% flatten_2(T, L0, L) is true iff L is the list that results from
	% traversing T left-to-right depth-first, and then appending L0.
tree__flatten_2(empty, L, L).
tree__flatten_2(node(T), L, [T|L]).
tree__flatten_2(tree(T1,T2), L0, L) :-
	tree__flatten_2(T2, L0, L1),
	tree__flatten_2(T1, L1, L).

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

tree__is_empty(empty).
tree__is_empty(tree(L, R)) :-
	tree__is_empty(L),
	tree__is_empty(R).

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