Bratko, Chapter 2: Syntax and Meaning

- data objects in Prolog [Fig 2.1]
  - atoms
    - strings of letters/digits/_ starting with lowercase letter
      - yes, parent, female, tom, tom_jones
    - strings of special characters (some have predefined meanings)
    - strings of characters enclosed in single quotes
      - 'Tom Jones'
  - numbers: [-][0-9]*[.][0-9]*
    - 2.71, -100.5, 0.5 (but not .5)
  - variables
    - strings of letters/digits/_ starting with uppercase letter or _
    - anonymous variable _
      - haschild(X) :- parent(X,Y).
        - OR haschild(X) :- parent(X,_).
      - ?- parent(X,_).  doesn' print children
      - parent(_,_) different from parent(X,X)
  - structures
    - functor(arg1,arg2,...)
      - e.g., date(2,october,1964)
      - arguments can be constants, variables or other structures
      - defined by Name and Arity, e.g., date/3 (differs from date/2)
        - e.g., X is *(4,3)  same as  X is 4*3
    - e.g., binary_tree(binary_tree(a,b),binary_tree(c,binary_tree(d,e))).
- matching: most general unifier
  - the '=' operator '=(Exp1,Exp2)'
  - e.g.
    | ?- date(D1,M1,1983) = date(D2,map,Y2).

    D1 = D2 = _8890,
    M1 = map,
    Y2 = 1983 ;

    no
  - no occurs checking (Y = foo(Y))
  - problem-solving with just matching
- disjunction
  - P :- Q.  P :- R,S. --> P :- Q;R,S.
  - predecessor(X,Z) :-
        parent(X,Z);
        parent(X,Y),
        predecessor(Y,Z).