Class 09: Prolog (2)

Held: Friday, 11 February 2011

Summary: We consider Prolog's lists and mathematical operations.

Related Pages:

• EBoard.
• Lab: Prolog (2).
• Reading: Tate 4.3.

Notes:

• HW4 to be posted some time tonight. (I had started to design one assignment, but discarded it after spending too much time trying to solve it myself.)
• EC for CS Table today. Reading: Wikipedia on Nearest Neighbor.

Overview:

• Math in Prolog.
• Lists in Prolog.
• Concatenating Lists.
• Lab.

Math in Prolog

• While we could define all of the mathematical operations ourselves (hmmm ... there's an interesting homework problem), it is more efficient to have them built in to Prolog.
• The basic math model in Prolog is that you can write thing = expression.
• Prolog evaluates the expression.
• If the thing is a constant, it compares the two results and returns true or false depending on the result of the comparison.
• If the thing is a variable, it updates the table of variable values and returns true.

Lists in Prolog

• Prolog has lists built from cons cells, plus lots of syntactic sugar.
• [] is the empty list.
• [H|T] is what you might think of as 'cons'ing H and T.
• [X,Y,Z] is a three-element list.
• [X,Y|T] is a list with at least two elements (X and Y) and remainder T.

Concatenating Lists

• Two approaches (one obvious, one the funky Tate approach).
• We'll look at both.

Lab

• Do the lab.
• Be prepared to reflect.