?- use_module(library(random)).


% this predicate loops as follows: It asks the user for a cmd. If it is
% listing, a listing is done. If random, then a random number is
% written. If it is end, then the loop quits. Anything else, and an
% error message is written.

% This version of the program uses recursion to continually loop.
% The only time recursion doesn't happen is if 'quit' is entered.
% The cuts are used to prevent backtracking.

cmdLooper :-
	write('enter command (listing, random, or quit): '),
	read(Term),
	do_cmd(Term).
	
do_cmd(quit) :-
	!,
	write('Quitting.'), nl.
do_cmd(listing) :-
	write('Listing...'),
	nl,
	listing,
	!,
	cmdLooper.
do_cmd(random) :-
	write('Random number: '),
	random(X),
	write(X),
	nl,
	!,
	cmdLooper.
do_cmd(X) :-
	write('No siree Bob! Bad command: '), 
	write(X),
	write('.'),
	nl,
	!,
	cmdLooper.