Intelligent systemsLection 5

Logic programming in Prolog

Syntax of Prolog

:- implication or ←, conjunction; disjunction. End of clause _ name of variable, unused in later process of interpretation

(anonimous variable)

grandmother(X,Y) :- mother(X,Z), parent(Y,Z). Clause-rule

mother(cathy, donald). Clause-fact

Solving of task in PrologSolving of task in Prolog (or interpretation of program) is based on unification ( kind of backward inference).Unification began from predicate-goal, which is needed to prove.And system try to use all possible cases corresponding to goal.Current proving predicate is current goal. During this process if attempt prove to be fail then system return back and try to use alternative case.So solving of task is search of any tree of goals.

Simple programPREDICATESlittle (symbol)middle (symbol)big (symbol)strong (symbol)powerful (symbol)

CLAUSESlittle (cat).little (wolf).middle (tiger).middle (bear).big (elephant).big (hippopotamus).strong (tiger).powerful (Animal):- middle (Animal), strong (Animal).powerful (Animal):- big (Animal).

Goal: powerful (Animal).

Try to use rule 1try to prove middle(Animal)found fact middle(tiger) Animal = tigertry to prove strong(tiger) found fact strong(tiger)

Powerful(Animal) is proved Animal = tiger

Goal: powerful (elephant).

Try to use rule 1try to prove middle(elephant)fail return back (redo)

Try to use rule 2try to prove big(elephant)found fact big(elephant)

Goal is proved

Goal: father(adam,X) Result: father(adam,bill)Who is kids of adam? father(adam,beth)

X=bill, X=bethGoal: father(X,bill) Result: father(adam,bill)Who is father of bill? X=adamGoal: grandparent(X,cathy)

solving: grandparent(X,cathy) :- parentX,Y), parent(Y,cathy)parent(X,Y) :- father(X,Y) try with redo until Y=cathyresult: parent(bill,cathy) X=bill, Y=cathy

grandparent(X,Z) :- parent(X, Y ), parent(Y,Z).parent(X, Y ) :- father (X, Y ).parent(X, Y ) :- mother(X, Y ).father (adam, bill). mother(anne, bill).father (adam, beth). mother(anne, beth).father (bill, cathy). mother(cathy, donald).father (donald, eric). mother(diana, eric).female(anne). male(adam).female(beth). male(bill).female(cathy). male(donald).female(diana). male(eric).

parent(bill, cathy) :- father(bill,cathy)result: parent(bill,cathy)

grandparent(X,cathy) is proved with X=bill

Lists and recursion in PrologList may be described in 2 forms:

[donald, peter, nick] - enumeration

[A | Z] - fragmentation in head and tail[donald | Z]

In last case as result of unification Z=[peter, nick]

Fragmentation of lists is foundation of recursive programs

Recursion without lists

PREDICATESfactorial (integer, integer)CLAUSES%factorial 0! equal 1factorial (0, 1):- !.%factorial n! equal to factorial (n–1)!, multiplied by nfactorial (N, Factorial_N):- M=N–1, factorial (M, Factorial_M),Factorial_N=Factorial_M*N.GOALwrite (“Input number for calculation of factorial? ”), readint (Number),factorial (Number, Result), write (Number, “!=”, Result).

Calculation 3!

PDC-Prolog.Sections of program

• CLAUSES contains clauses (main part)• PREDICATES contains descriptions of predicates

(its structure), used in program• DOMAINS contains descriptions of domains

(types of arguments of predicates)• GOAL contains predicate-goal used for start of program• DATABASE contains variable part of program, e. i.

descriptions of predicates-facts which may be adding and removing during execution of program

• CONSTANTS contains constants

Example of program/* PROBLEM:A farmer with his goat, wolf and cabbage come to a river that theywish to cross. There is a boat, but it only has room for two, andthe farmer is the only one that can row. If the goat and cabbageget in the boat at the same time, the cabbage gets eaten.Similarly, if the wolf and goat are together without the farmer,the goat is eaten. Devise a series of crossings of the river so that allconcerned make it across safely.

The state of the system is indicated by stating where the farmer, the goatthe wolf and the cabbage are located. state( Farmer, Wolf, Goat, Cabbage )

The problem is that a state must only be visited once, and some states are illegal. This is checked by 'unsafe' and 'member'.

The Predicate "go" can be called with a start state and a final state

go( state(east,east,east,east), state(west,west,west,west) ).*/

DOMAINS LOC = east ; west STATE = state(LOC,LOC,LOC,LOC) PATH = STATE*PREDICATES go(STATE,STATE) /* Start of the algorithm */ path(STATE,STATE,PATH,PATH) /* Finds a path from one state to another */ move(STATE,STATE) /* Transfer a system from one side to another */ opposite(LOC,LOC) /* Gives a location on the opposite side */ unsafe(STATE) /* Gives the unsafe states */ member(STATE,PATH) /* Checks if the state is already visited */ write_path(PATH) write_move(STATE,STATE) show_move(STATE,STATE) showside(LOC,LOC,string) s_riverGOAL makewindow(4,7,0,"",0,0,24,80), makewindow(3,7,7," The River ",15,0,10,80), makewindow(2,112,0,"",0,0,1,80), write("press any key for each step of solution"), makewindow(1,7,7," Solutions ",2,0,13,80), show_move(state(west,west,west,west),state(west,west,west,west)),

go(state(east,east,east,east),state(west,west,west,west)),write("solved press any key to continue"),readchar(_), exit.

CLAUSES go(S,G):- path(S,G,[S],L), nl,write("A solution is:"),nl, write_path(L), fail. go(_,_). path(S,G,L,L1):- move(S,S1), not( unsafe(S1) ), not( member(S1,L) ),

path( S1,G,[S1|L],L1),!. path(G,G,T,T):- !. /* The final state is reached */move(state(X,X,G,C),state(Y,Y,G,C)):-opposite(X,Y). /* FARMER + WOLF */ move(state(X,W,X,C),state(Y,W,Y,C)):-opposite(X,Y). /* FARMER + GOAT */ move(state(X,W,G,X),state(Y,W,G,Y)):-opposite(X,Y). /* FARMER + CABBAGE */ move(state(X,W,G,C),state(Y,W,G,C)):-opposite(X,Y). /* ONLY FARMER */ opposite(east,west). opposite(west,east):-!. unsafe( state(F,X,X,_) ):- opposite(F,X). /* The wolf eats the goat */ unsafe( state(F,_,X,X) ):- opposite(F,X). /* The goat eats the cabbage */ member(X,[X|_]). member(X,[_|L]):-member(X,L). write_path( [H1,H2|T] ) :- !, readchar(_), write_move(H1,H2), show_move(H1,H2), write_path([H2|T]). write_path( [] ).

write_move( state(X,W,G,C), state(Y,W,G,C) ) :-!, write("The farmer crosses the river from ",X," to ",Y),nl. write_move( state(X,X,G,C), state(Y,Y,G,C) ) :-!, write("The farmer takes the Wolf from ",X," of the river to ",Y),nl. write_move( state(X,W,X,C), state(Y,W,Y,C) ) :-!, write("The farmer takes the Goat from ",X," of the river to ",Y),nl. write_move( state(X,W,G,X), state(Y,W,G,Y) ) :-!, write("The farmer takes the cabbage from ",X," of the river to ",Y),nl./* Show them move across the river.*/ show_move( state(F,W,G,C), state(F1,W1,G1,C1) ) :-!, s_river, showside(F,F1,"Farmer "), showside(W,W1," Wolf "), showside(G,G1," Goat "), showside(C,C1,"Cabbage"), shiftwindow(1). showside(east,east,Item):-!, write(" ~~~~~ ",Item),nl. showside(west,west,Item):-!, write(" ",Item," ~~~~~ "),nl. showside(east,west,Item):-!, write(" ",Item," <= <= <= ",Item),nl. showside(west,east,Item):-!, write(" ",Item," => => => ",Item),nl.s_river:- shiftwindow(3),clearwindow, write(" WEST river EAST"),nl, write(" ----------------------------------------------------------------------"), nl.

Main operators of PDC-Prolog

INPUT--------

readln(StringVariable)(string) - (o)

readint(IntgVariable)(integer) - (o)

readreal(RealVariable)(real) - (o)

readchar(CharVariable)(char) - (o)

file_str(OSFileName,StringVariable) File <--> String(string,string) - (i,o) (i,i)

inkey(CharVariable)(Char) - (o)

keypressed()

OUTPUT======

write( Variable|Constant * )nl()writef( FormatString, Variable|Constant* )

In the format string the following options are known after a percentage sign: %d Normal decimal number. (chars and integers) %u As an unsigned integer. (chars and integers) %R As a database reference number. (database reference numbers) %X As a long hexadecimal number. (strings, database reference numb). %x As a hexadecimal number. (chars and integers). %s Strings. (symbols and strings). %c As a char. (chars and integers). %g Reals in shortest posible format (default for reals) %e Reals in exponetial notation %f Reals in fixed notation %lf Only for C compatibility (fixed reals)

\n - newline\r - carriage return\t - tabulator\nnn - character with code nnn

FILESYSTEM==========

openread(SymbolicFileName,OSFileName)(file,string) - (i,i)

openwrite(SymbolicFileName,OSFileName)(file,string) - (i,i)

openappend(SymbolicFileName,OSFileName)(file,string) - (i,i)

openmodify(SymbolicFileName,OSFileName)(file,string) - (i,i)

openfile(SymbolicFileName,OSFileName,OpenMode,FileAttribute,CreateFlag)

(file,string,integer,integer,integer) - (i,i,i,i,i)

WINDOW SYSTEM=============

makewindow(WindowNo,ScrAtt,FrameAtt,Framestr,Row,Column,Height,Width)(integer,integer,integer,string,integer,integer,integer,integer)- (i,i,i,i,i,i,i,i) (o,o,o,o,o,o,o,o)

makewindow(WindowNo,ScrAtt,FrameAtt,TitleStr,Row,Column,Height,Width,ClearWindow,TitlePos,BorderChars)

(integer,integer,integer,string,integer,integer,integer,integer,integer,integer,string)

- (i,i,i,i,i,i,i,i,i,i,i)- (o,o,o,o,o,o,o,o,o,o,o)ClearWindow: 0=Don't clear window after creation, 1=do clear.TitlePos: Title pos, value=255 centers title.BorderChars: A 6 character string to build frame.

1st char: Upper left corner2nd char: Upper right corner3rd char: Lower left corner4th char: Lower right corner5th char: Horizontal line6th char: Vertical line

Ex. "┌┐└┘─│" for a single borderor "╔╗╚╝═║" for a double border

shiftwindow(WindowNo)(integer) - (i) (o)

STRING HANDLING===============

frontchar(String,FrontChar,RestString)(string,char,string) - (i,o,o) (i,i,o)(i,o,i) (i,i,i) (o,i,i)

fronttoken(String,Token,RestString)(string,string,string) - (i,o,o) (i,i,o)(i,o,i) (i,i,i) (o,i,i)

frontstr(Length,Inpstring,StartString,RestString)(integer,string,string,string) - (i,i,o,o)

substring(String,First,NBytes,SubString)(string,integer,integer,string) - (i,i,i,o)

subchar(String,CharNo,Char)(string,integer,char) - (i,i,o)

searchstring(String,SearchStr,FoundPos)(string,string,integer) - (i,i,o)

searchchar(String,Char,FoundPos)(string,char,integer) - (i,i,o)

concat(String1,String2,String3) String3 = String1 + String2(string,string,string) - (i,i,o) (i,o,i)(o,i,i) (i,i,i)

str_len(String,Length)(string,integer) - (i,i) (i,o) (o,i)

isname(StringParam)(string) - (i)

CONVERSIONS===========

char_int(CharParam,IntgParam)(char,integer) - (i,o) (o,i) (i,i)

str_int(StringParam,IntgParam)(string,integer) - (i,o) (o,i) (i,i)

str_char(StringParam,CharParam)(string,char) - (i,o) (o,i) (i,i)

str_real(StringParam,RealParam)(string,real) - (i,o) (o,i) (i,i)

upper_lower(StringInUpperCase,StringInLowerCase)(string,string) - (i,i) (i,o) (o,i)

upper_lower(CharInUpperCase,CharInLowerCase)(char,char) - (i,i) (i,o) (o,i)

str_ref(Str,Ref)(string,ref) - (i,o) (o,i) (i,i)

real_ints(Real,I1,I2,I3,I4)(real,integer,integer,integer,integer) - (i,o,o,o) (o,i,i,i)

HANDLING THE INTERNAL DATABASE==============================

consult(OSFileName)(string) - (i)

consult(OSFileName,InternalDatabaseName)(string,InternalDatabaseName) - (i,i)

save(OSFileName)(string) - (i)

save(OSFileName,InternalDatabaseName)(string,DatabaseName) - (i,i)

assert( Term )(InternalDatabaseDomain) - (i)

asserta( Term )(InternalDatabaseDomain) - (i)

assertz( Term )(InternalDatabaseDomain) - (i)

SCREEN HANDLING===============EXTERNAL DATABASE SYSTEM========================BGI GRAPHIC===========EDITOR======STATUS LINES============OS RELATED===========MISCELLANEOUS MACHINE LOWLEVEL===============================ERROR & BREAK CONTROL=====================MESSAGE SUBSYSTEM=================MISCELLANEOUS=============CONTROL PREDICATES==================ARITHMETIC==========