CSC302 2011S, Class 09: Prolog (2)

Overview:
* Math in Prolog.
* Lists in Prolog.
* Concatenating Lists.
* Lab.

Admin:
* Cocoa
* Missing: SA, AC
* 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.

Day One:
* Prolog is a DECLARATIVE programming language with emphasis on predicate
  logic.
* Syntax.

"It's not a real programming language unless you can do math"
* You can do math with predicate logic
  add(zero,X,X).
  add(s(X),Y,Z) 
* For efficiency and uniformity and accuracy, build it in
  thing is expression: A goal or claim
  * Evaluation:
    Evaluate the expression as you would evaluate any mathematical expression
    If the thing on the left is a number, compare and return the result
     of the comparison
    If the thing on the left is a variable, assign and return true

"It's not a real programming language unless you have data structures"
Lists
* Syntactic sugar makes life more fun (or more confusing)
* empty list: []
* cons [H|T]
* Get car and cdr
  car([H|_], H).
  cdr([_|T], T).
* More sugar
  [a,b,c]
  [a,b|T]$a

Tate's problem: How do we concatenate two lists together?

concat(L1,L2,L3) - L3 is the result of concatenating L1 and L2.

concat([], L, L).
concat([H|T], L2, L3) :- concat(T,L2,Int), L3 = [H|Int].

concatenate([], L, L).
concatenate([H|T1], L2, [H|T3]) :- concatenate(T1, L2, T3).

Lab!

For add_to_end problem, you base case should probably be

add_to_end([], V, [V]).