Prolog Data Objects

Atoms

• String of letters and digits
• Start with lower case letter
• yes, parent, female, tom, tom_jones
• String of characters enclosed in single quotes ('Tom Jones')

Numbers [-][0-9]*[.][0-9]*

• 2.71, -100.5, 0.5 (but not .5)

Variables

• String of letters and digits
• Start with upper case letter (or _, anonymous variable)
• Universally quantified

Structures

• functor(arg1, arg2, $\ldots$)
• date(2, october, 1964)
• Arguments can be constants, variables, or other structures
• Defined by Name and Arity (date/3 different from date/2)