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ITEC 380. Organization of programming languages Lecture 10 – Prolog. Review. Homework 2 due on F Semester project will be out either F or M C# picked as OO Language Lists Recursion. Objectives. Review Prolog Look at GUIs with Prolog. Exercise.
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ITEC 380 Organization of programming languages Lecture 10 – Prolog
Review • Homework 2 due on F • Semester project will be out either F or M • C# picked as OO Language • Lists • Recursion
Objectives • Review Prolog • Look at GUIs with Prolog
Exercise • How do you create a set of facts/rules in Prolog that can read in five numbers and store them a stack of numbers? • How would you reverse the contents of the list? • How would you pop off the top 2 and add the result to the top of the stack?
Review • How would you represent that Bill has five dollars and Ted has two in Prolog? • How would your represent a purchase of an item that costs three dollars? • How would you add two numbers and print out if the result is greater than 5? • How would you change the previous example to allow user input?
Methods of reversing • Accumulator versus appending • How do we tell which one is better? naiverev([],[]). naiverev([H|T],R):- naiverev(T,RevT), append(RevT,[H],R). Versus accRev([H|T],A,R):- accRev(T,[H|A],R). accRev([],A,A). rev(L,R):- accRev(L,[],R).
XPCE • A system for creating GUIs using prolog • Demo of capabilities • Type manpce in your prolog interpreter
Basics • Four predicates for controlling GUIs • New, send, get free • Java GUI components comparison • Example of creating a GUI with prolog new(@demo, dialog(“Demo Window”)). send(@demo, open).
Components • To add to the window you use send • send(@demo, append(text_item(‘Hello’)). • Capabilities • button (name, RuleToCall). • int_item %Integer with bump up/down • slider %Numerical value in a range • menu %Radio button, tick-box, combo-box • label %Images / Text • list_browser %View a list of data • editor %Allow editing of data
Example program ask_employee :- new(Dialog, dialog('Define employee')), send_list(Dialog, append, [ new(N1, text_item(first_name)), new(N2, text_item(family_name)), new(S, new(S, menu(sex))), new(A, int_item(age, low := 18, high := 65)), new(D, menu(department, cycle)), button(cancel, message(Dialog, destroy)), button(enter, and(message(@prolog, assert_employee, N1?selection, N2?selection, S?selection, A?selection, D?selection), message(Dialog, destroy))) ]),
Continuing on send_list(S, append, [male, female]), send_list(D, append, [research, development, marketing]), send(Dialog, default_button, enter), send(Dialog, open).
Example 2 • Get a name ask_name(Name) :- new(D, dialog('Prompting for name')), send(D, append, new(TI, text_item(name, ’’))), send(D, append, button(ok, message(D, return, TI?selection))), send(D, append, button(cancel, message(D, return, @nil))), send(D, default_button, ok), % Ok: default button get(D, confirm, Answer), % This blocks! send(D, destroy), Answer \== @nil, % canceled Name = Answer.
Shapes • Can get creative send(@p, display, new(@bo, box(100,100))). send(@p, display, new(@ci, circle(50)), point(25,25)). send(@p, display, new(@tx, text(’Hello’)), point(120, 50)). send(@p, display,new(@bz, bezier_curve(point(50,100), point(120,132), point(50, 160), point(120, 200)))).
Display • Can get the information from the GUI • get(@demo, display, D). %Display var • get(@display, size, Size) • get(Size, width, W)
Process • Find basic component idea • Find out arguments • Figure out when to call new, send, get • Build it piece by piece
GUIs • What is your opinion of Prolog’s GUI implementation? • What are it’s strengths? • What are it’s weaknesses? • If you wanted to do something other than this GUI with prolog, what would you do (hint, covered previously)?
Next week • C#
