%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% 								     %
%  Miscellaneous Functions Needed by Expert System Shells	     %
% 								     %
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%


member(Element,[Element|List]).
member(Element,[_|List]):-member(Element,List).


append([],List,List).
append([E1|L1],L2,[E1|L3]):-append(L1,L2,L3).


replace([OF|OM],OF,NI,[NI|OM]).
replace([OF|OM],OI,NI,[OF|NL]):-replace(OM,OI,NI,NL).

remove([OF|OM],OF,OM).
remove([OF|OM],OI,[OF|NL]):-remove(OM,OI,NL).

insert(OldList,Item,NewList):-
	append(LeftPart,RightPart,OldList),
	append(LeftPart,[Item|RightPart],NewList).


% Satisfy goal at most once.
%
:-op(900,fx,once).
once Goal:-Goal,!.

% Procedures for console output using a C++-like insertion 
% operator. (A simpler implementation can be found in file str.pro.)
%
%
% Sample uses:
%
% ?-human(X),sOut<<"The name "<<X<<" belongs to a human.".
% % This will print the text on the console.
%
% ?-human(X),Y<<"The name "<<X<<" belongs to a human.". 
% % This will unify Y with the list of ASCII codes corresponding
% % to the text.
%
% ?-sOut<<"Text"<<<"List".
 % This will print: Text[76,105,115,116][];
% the first item is considered text, the other is taken as a Prolog term.

:-op(700,xfy,<<).	% The insertion operator.
:-op(700,xfy,<<<).	% Prolog term insertion operator.

% A procedure to print a list of ASCII codes as text.
%
puts([]).
puts([First|More]):-put(First),puts(More).

<<(Sout,Rest):-nonvar(Sout),Sout=sOut,!,
	<<(TextL,Rest),puts(TextL),!.
<<(Stream,Var):-var(Var),Stream=Var.
<<(Stream,Args):-
	Args=..[Op,First,More],(Op='<<' ; Op='<<<'),
	stp(First,Stream,Hole),
	Remain=..[Op,Hole,More],Remain.
<<(Hole,hole(Hole)).
<<(Stream,Only):-
	stp(Only,Stream,[]),!.

<<<(Sout,Rest):-nonvar(Sout),Sout=sOut,!,
	<<<(TextL,Rest),puts(TextL),!.	
<<<(Stream,Args):-
	Args=..[Op,First,More],(Op='<<' ; Op='<<<'),
	stps(First,Stream,Hole),
	Remain=..[Op,Hole,More],Remain.
<<<(Stream,Only):-
	stps(Only,Stream,[]),!.

% The folowing procedures convert terms to a sequence of ASCII codes.
% 
% The stps(Item,Stream,Hole) procedure converts Item, interpreting it as a
% prolog term, to a sequence of ASCII codes. Stream consists of these codes
% with Hole appended.
%
% The stp(Item,Stream,Hole) procedure is similar, except Item could be
% a print command or a sequence of ASCII codes.
%
stp(Unbound,Stream,Hole):-		% Error for unbound variable.
	var(Unbound),!,
	append("** Unbound variable. **",Hole,Stream).
stp(Atom,[10|Hole],Hole):-		% New line.
	nonvar(Atom),Atom=nl,!.
stp([First|More],Stream,Hole):-		% List of ASCII codes.
	integer(First),
	append([First|More],Hole,Stream).
stp(Item,Stream,Hole):-			% List or structure.
	stps(Item,Stream,Hole).

stps([],Stream,Hole):-Stream<<hole(Hole).
stps([First|More],Stream,Hole):-!,
	H2<<"]"<<Hole,
	Stream<<"["<<H1,
	conList([First|More],H1,H2).
stps(Struct,Stream,Hole):-
	Struct=..[Functor|Comps],
	conAtom(Functor,Stream,H3),
	once ( Comps=[],H3=Hole
	      ;
	      H3<<"("<<H1,conList(Comps,H1,H2),H2<<")"<<hole(Hole)
	    ).

% Convert a list of items to a list of ASCII codes, formatting as Prolog.
%	
conList([Last],Stream,Hole):-Stream<<<Last<<hole(Hole).
conList([Next|More],Stream,Hole):-
	conList(More,H1,Hole),
	Stream<<<Next<<","<<hole(H1).

% Convert an atom to a list of ASCII codes.
%
conAtom(Atom,Stream,Hole):-
	name(Atom,AtomL),append(AtomL,Hole,Stream).