Full Logic Programming

Data structures Pure LP allows only to represent relations (=predicates) To obtain full LP we will add functors (=function symbols) This will allow us to represent data structures

Data structures Pure LP allows only to represent relations (=predicates) To obtain full LP we will add functors (=function symbols) This will allow us to represent data structures In particular, functors can be nested

Data structures Pure LP allows only to represent relations (=predicates) To obtain full LP we will add functors (=function symbols) This will allow us to represent data structures In particular, functors can be nested

Functor examples cons(a,[ ]) describes the list [a]. [ ] is an individual constant, standing for the empty list. The cons functor has a syntactic sugar notation as an inx operator |: cons(a,[ ]) is written: [a|[ ]]. cons(b,cons(a,[ ])) the list [b,a], or [b|[a|[ ]]]. The syntax [b,a] uses the printed form of lists in Prolog. tree(Element,Left,Right) a binary tree, with Element as the root, and Left and Right as its sub-trees. tree(5,tree(8,void,void),tree(9,void,tree(3,void,void)))

Capturing natural number arithmetics 1. Definition of natural numbers: % Signature: natural_number(N)/1 % Purpose: N is a natural number. natural_number(0). natural_number(s(X)) :- natural_number(X).

Addition and substraction % Signature: Plus(X,Y,Z)/3 % Purpose: Z is the sum of X and Y. plus(X, 0, X) :- natural_number(X). plus(X, s(Y), s(Z)) :- plus(X, Y, Z). ?- plus(s(0), 0, s(0)). /* checks 1+0=1 Yes. ?- plus(X, s(0), s(s(0)). /* checks X+1=2, e.g., minus X=s(0). ?- plus(X, Y, s(s(0))). /* checks X+Y=2, e.g., all pairs of natural numbers, whose sum equals 2 X=0, Y=s(s(0)); X=s(0), Y=s(0); X=s(s(0)), Y=0.

Less or Equal % Signature: le(X,Y)/2 % Purpose: X is less or equal Y. le(0, X) :- natural_number(X). le(s(X), s(Z)) :- le(X, Z).

Multiplication % Signature: Times(X,Y,Z)/2 % Purpose: Z = X*Y times(0, X, 0) :- natural_number(X). times(s(X), Y, Z) :- times(X, Y, XY), plus(XY, Y, Z).

Implications Pure LP can’t capture unbounded arithmetics. It follows that full LP is strictly more expressible than pure LP – In facts full LP is as expressible as Turing Machines Full LP is undecidable – In RE: if there is a proof we will find it, but if not we may fail to terminate Proofs may be of unbounded size since unification may generate new symbols through repeated substitutions of variables x with f(y).

Data Structures % Signature: binary_tree(T)/1 % Purpose: T is a binary tree. binary_tree(void). binary_tree(tree(Element,Left,Right)) :- binary_tree(Left),binary_tree(Right). % Signature: tree_member(X, T)/2 % Purpose: X is a member of T. tree_member(X, tree(X, _, _)). tree_member(X, tree(Y,Left, _)):- tree_member(X,Left). tree_member(X, tree(Y, _, Right)):- tree_member(X,Right).

Lists Syntax: [ ] is the empty list. [Head|Tail] is a syntactic sugar for cons(Head, Tail), where Tail is a list term. Simple syntax for bounded length lists: [a|[ ]] = [a] [a|[ b|[ ]]] = [a,b] [rina] [sister_of(rina),moshe|[yossi,reuven]] = [sister_of(rina),moshe,yossi,reuven] Defining a list: list([]). /* defines the basis list([X|Xs]) :- list(Xs). /* defines the recursion

Lists Syntax: [ ] is the empty list. [Head|Tail] is a syntactic sugar for cons(Head, Tail), where Tail is a list term. Simple syntax for bounded length lists: [a|[ ]] = [a] [a|[ b|[ ]]] = [a,b] [rina] [sister_of(rina),moshe|[yossi,reuven]] = [sister_of(rina),moshe,yossi,reuven] Defining a list: list([]). /* defines the basis list([X|Xs]) :- list(Xs). /* defines the recursion

List membership: % Signature: member(X, List)/2 % Purpose: X is a member of List. member(X, [X|Xs]). member(X, [Y|Ys]) :- member(X, Ys)

List membership: % Signature: member(X, List)/2 % Purpose: X is a member of List. member(X, [X|Xs]). member(X, [Y|Ys]) :- member(X, Ys)

Append append([], Xs, Xs). append([X|Xs], Ys, [X|Zs] ) :- append(Xs, Ys, Zs). ?- append([a,b], [c], X). ?- append(Xs, [a,d], [b,c,a,d]). ?- append(Xs, Ys, [a,b,c,d]).

Append append([], Xs, Xs). append([X|Xs], Y, [X|Zs] ) :- append(Xs, Y, Zs). ?- append([a,b], [c], X). ?- append(Xs, [a,d], [b,c,a,d]). ?- append(Xs, Ys, [a,b,c,d]).

Reverse reverse([], []). reverse([H|T], R) :- reverse(T, S), append(S, [H], R). OR reverse(Xs, Ys):- reverse_help(Xs,[],Ys). reverse_help([X|Xs], Acc, Ys ) :- reverse_help(Xs,[X|Acc],Ys). reverse_help([ ],Ys,Ys ).