Bratko, Chapter 7: More Built-in Procedures

7.1 Testing the type of terms
- var(X) is true if X is an uninstantiated variable
- nonvar(X) is true if X is a term other than a variable, or X is an
  instantiated variable
- atom(X) is true if X "stands for" (is or is instantiated as) an atom
- integer(X) is true if X stands for an integer
- float(X) is true if X stands for a floating point number (no real(X))
- atomic(X) is true if X stands for an integer or atom
- examples
  - cryptarithmetic (fig7.2)

7.2 Constructing and decomposing terms: =.., functor, arg, name
- (Term =.. L)
  - true if L is a list whose first element is the functor of Term and
    whose remaining elements are the arguments of Term 
  -  can construct or decompose terms
  - examples
    - operation on arguments for different-sized argument lists
    - subterm substitution [Fig7.3]
    - goal construction (call(G) instead of G)
- functor(Term,F,N)
  - true if F is the functor of Term and N is the arity of F
- arg(N,Term,A)
  - true if A is the Nth argument in Term
  - arguments number left to right from 1

7.3 Various kinds of equality
- (X = Y) is true if X and Y match (pattern match)
- (X is E) is true if X matches the value of the arithmetic expression E
- (E1 =:= E2) is true if the arithmetic expressions E1 and E2 are equal
- (E1 =\= E2) is true if the arithmetic expressions E1 and E2 are not equal
- (T1 == T2)
  - true if terms T1 and T2 are identical
  - even variables must have same names
- (T1 \== T2) is true if T1 and T2 are not identical
- examples
  - count (p176)

7.4 Database Manipulation
- assert(C) always succeeds and adds clause C to the database
- retract(C) deletes a clause that matches C
  - deletes more than one such clause upon backtracking
- examples
  - assert(man(plato)).
  - assert( (mortal(X) :- plato(X)) ).
- asserta(C) adds C at the beginning of the database
  - can be used to store solutions
    - solve(problem1,Solution), asserta(solve(problem1,Solution)).
    - called memoization, caching, speedup learning
- assertz(C) adds C at the end of the database
- example 'maketable' on page 180

7.5 Control facilities
- review: !, fail, true, not(P) :- P,!,fail., call(P)
- repeat: iteration through backtracking
  - defined: repeat.
             repeat :- repeat.
  - use: repeat, set_up, (stopping_condition, !; loop_body, fail).

7.6 bagof, setof, findall
- when you want to remember all solutions in a list
  - typically lost through backtracking
- bagof(X,P,L)
  - true if the list L is all the objects X such that P is satisfied
  - can use the ^ operator to ignore variables (existentially quantify them)
    - X ^ P means there exists an X such that P is true (i.e., X ignored)
- setof(X,P,L)
  - true if the list L is all the objects X such that P is satisfied
  - arguments in L are ordered with no duplicates
- findall(X,P,L) [Fig7.4]
  - true if the list L is all the objects X such that P is satisfied
  - ignores differences in non-X variables in P (like the ^ operator)
- see example starting on 182
  - likes(X,Y)
  - setof((Y,S), setof(X,likes(X,Y),S), SS).

HW
- Exercise 7.1, page 169.
- Exercise 7.3, page 174.
- Exercise 7.8, page 184.
- hard
  - Exercise 7.4, page 174.
  - Exercise 7.5, page 174.