%% lists.pl
%%
%% Author(s):
%%
%% CS 60 Hw 4, part 1
%%
%%
%% Some "nice" prolog settings:
%% See www.swi-prolog.org/pldoc/man?predicate=current_prolog_flag/2
%% This one prompts only when there are variables:
:- set_prolog_flag( prompt_alternatives_on, groundness ).
% This one sets some reasonable display defaults:
:- set_prolog_flag(toplevel_print_options,
	  [quoted(true),
	   portray(true),
	   attributes(portray),
	   max_depth(999),
	   priority(699)]).


%% a couple of example predicates that might be helpful...

%
% member( E, L ) should be true if
%         E is a top-level member of the list L
% member should work when E is a variable or bound to a value;
%         L should only be bound to a value
%
member( E, [E|_] ).
member( E, [_|R] ) :- member( E, R ).


%
% reverse( L, Rev ) should be true if Rev is the reverse of L
% reverse should work when Rev is a variable or bound;
%          L should only be bound to a value
%
reverse( [], [] ).   % base case ~ though they don't always involve [] in Prolog!
reverse( [F|R], Rev ) :- reverse( R, Tmp ), append( Tmp, [F], Rev ).


%
% has42( L ) should be true if L contains the element 42 at the top
% level
%
has42( [42] ).
has42( [_|R] ) :- has42( R ).



%% Here are commented-out placeholders for this week's predicates...
%% Be sure to comment each predicate you write!



%% removeOne( E, L, NewL )


%% count( E, L, N )


%% find( Pattern, Target, Index )


%% depth( E, Tree, N )




% a helper predicate to define a tree
tree1( [ 42, [ 20, [10, [5, [], []], [18, [], []]], [] ],
             [ 100, [67, [50, [], []], []], [150, [], [2009, [], []]] ] ] ).


%% insert( E, Tree, NewTree )


%% path( A, B, Graph, Path )


% a helper predicate to define a graph
graph1(  [ [a,b], [b,c], [c,d], [b,w], [w,x], [x,z], [b,z] ] ).