PROLOG TOOLS

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INDEX:

• Symbols
• Syntax
  • Characters and Terms
    • Predicate
      • Built In
    • Arity
    • Clauses
  • Operators
  • Queries
• Sample Code/Syntax

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SYMBOLS

SYMBOL	DESCRIPTION	EXAMPLES
( )	Enclose objects and follows the relationship.	likes(john,mary).
.	Ends a fact, called the stop character.	likes(john,mary). human(socrates).
"Group of Facts"	A group of facts are called Data Bases.	male(albert). male(alice). female(alice). female(victoria). parents(edward,victoria,albert). parents(alice,victoria,albert).
"Capital Letters"	Words that start off with capital letters are variables.	?- likes(mary,X).
,	Separates two statements or objects.  when between two statements than it is conjunction   and means "and".	?- likes(mary,X), likes(john,X).
:-	The symbol for "if". Called a rule.	sister_of(X,Y) :- female(X), parents(X,M,F), parents(Y,M,F).
=	Equality and Matching	?- rides(clerk,bicycle) = X. policeman = policeman *[succeeds] bike(trek) = bike(X) *[X is instantiated to trek]
'	echo string	?- write('Hello World').
%	comment precursor	% My first program.
;	used after a query result that succceeds - means backtrack (unbinding of variable)	?- likes(john, X). X = mary ; X = wine ;
is	means '=', but everything after the '=' must be known or defined	f is c * 9.

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SYNTAX

• CHARACTERS
  • Uppercase (A,B,C,etc)
  • Lowercase (a,b,c,etc)
  • Digits (0,1,2,3,4,5,6,7,8,9)
  • Signs(+,-,*,\,/,~,^,<,>,:,.,?,@,#,$,&)
• TERMS (Sequence of Characters)
  • Constants
    • Atoms
      • Those that are made up of letters: likes mary john owns can_steal
        • Must begin with lowercase letters
        • If atom is enclosed in single quotes, atom may have any characters: 'Bill Martin'
        • the underline _ , can be used for readability in atoms
      • Those that are made up of signs: ?- :-
    • Integers
      • May not contain a decimal point
      • Normal range is from 0 to 16383
  • Variables
    • Like atoms except:
      • Start with capital letters or underline _
    • Anonymous variables
      • Just an underline _ , for when they will not be used anywhere else in the clause
  • Structures (compound terms, complex terms, facts)
    • Functor or Predicate
      • Names the general kind of structor in an ordinary program type language
      • Written before the Components/Arity
      • Built in predicates:
        • write().
        • nl().
        • tab().
        • fail().
    • Components (objects)/ Arity (fixed # of arguments)
      • Enclosed by round brackets
      • Separated by commas
      • Can be used inside other Components
    • Clauses
      • Each Predicate in a program is defined by their clauses (components)
      • Can be a fact or rule
• OPERATORS
  • Infix
    • Written between arguments
      • 3+4 (the + being the infix operator)
  • Prefix
    • Written before arguments
      • -3+4 (the - being the infix operator)
  • Postfix
    • Written after arguments
      • 3+4! (the ! being the infix operator)
  • Precedence (which operation to carry out first)
    • Precedence class
      • An iteger is associated with an operator
      • 1 being the highest precedence
    • Left or right associative
      • (+,-,/,*) are all left associative
        • 8/9/2 means (8/9)/2

• Equality and Matching
  • Infix operator written as"="
    • When '?- X=Y' is written Prolog attempts to match X and Y
    • When X is instantiated and Y is not than they become equal and Y takes on the value at X
    • When two structures have the same Functor and number of Components then all components become equal. For instance rides(clerk,bike) = rides(clerk,X); X becomes bike.
    • When neither variable is instantiated than when one becomes instantiated the other takes on that value. This is called share or co-refer.
    • RULE:
      • equal(X,Y) :- X=Y.
      • 'head' 'neck(:-)' 'body'
• QUERIES
  • Unification
    • The predicate is the same.
    • Same arity.
    • Arguments the same.
  • Binding
    • Variable takes on value of term it was matched with.
  • Process example

call ______________ exit
----->|              |----->
|     GOAL     |
|              |
<-----|              |<-----
fail ______________ redo

• RULES
  • Head
    • The predicate definition(just like a fact).
  • Neck
    • The neck symbol ':-' , reads as 'if'..
  • Body
    • One or more goals (a query).

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SAMPLE CODE/SYNTAX

CODE	DESCRIPTION	CALL/OUTPUT
mortal_report:- write('Known mortals are: '),nl, mortal(X), tab(3), write(X), nl, fail.	Report writing code. write is built in predicate meaning put on the screen. nl is built in predicate meaning new line. tab is built in predicate meaning tab over n number of spaces.	?- mortal_report. Known mortals are: socrates plato zeno aristotle no ?-
?- room(office).	goal(querypattern).	yes
room(X) :- location(X).	rule	?- room(living_room). yes
?- location(Thing, Place).	goal(querypattern x 2).	Thing = apple Place = kitchen
pred(arg1, arg2, ... argN).	Syntax for a fact.	IN CODE: customer('John Malcovich', boston, good_credit).
predicate_name/3	Syntax for a describing a record. means predicate_name with three arguments	customer('John Malcovich', boston, good_credit).
write('Known mortals are: ')	Syntax for a the Built in Predicate write/1	Known mortals are:
write('Known mortals are: '),nl, mortal(X)	Syntax for a the Built in Predicate nl/0	Known mortals are: socrates plato zeno aristotle
tab(3)	Syntax for a the Built in Predicate tab/1(integer)	yes
write(X), nl, fail.	Syntax for a the Built in Predicate fail/0	socrates plato zeno aristotle no ?-
?- room(office).	goal or query pattern	yes
?- location(Thing, Place).	two goals or query patterns	Thing = apple Place = kitchen
?- location(X, kitchen), edible(X).	compound query	X = apple

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