To load the database into the interpreter (assuming that you've saved the database into the directory you are running the interpreter in) you simply enter: ?. Queries lets you retrieve information from a logic program. The use of such a program is demonstrated by doing queries. In fact, a finite set of facts and or rules constitutes as a logic program. Prolog is a declarative language and you can read this database as follows:įor all X and Y, X is a child of Y if Y is a father of X or Y is a mother of X. Note that the here is like the or operator in other languages. Ī logic database contains a set of facts and rules.Ī complex term with only atoms as arguments is called a fact, while a complex term with variables as arguments is called a rule.Įxample of facts in Prolog: father_child(fred, susan).Įxample of a rule in Prolog: child_of(X,Y):. Eg father(john,doe), relative(a), mother(X,Y).
Name of a complex term is always an atom, while arguments can either be atoms or variables. Complex Terms - They are made from a functor and a sequence of arguments.Variables - A string which starts with an uppercase character or underscore ( _ ).Numbers - There is no special syntax for numbers, no declaration is required.Atoms - Any sequence of characters that do not start with an uppercase alphabet.
They allow us to reason about integers in a pure way. Generate all possible ways to append two lists to a given list: ?- append(A, B, ).ĬLP(FD) constraints are provided by all serious Prolog implementations. Notably, and as is typical for good Prolog code, append/3 can be used in several directions: It can be used to:Īppend two fully or partially instantiated lists: ?- A =, B=, append(A, B, Y)Ĭheck whether the relation is true for three fully instantiated lists: ?- A =, B =, C =, append(A, B, C) It defines a relation between three arguments and is true if the third argument is a list that denotes the concatenation of the lists that are specified in the first and second arguments.
Implemented in c#, javascript and phyton.
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