Page 70 - DCAP310_INTRODUCTION_TO_ARTIFICIAL_INTELLIGENCE_AND_EXPERT_SYSTEMS

Introduction to Artificial Intelligence & Expert Systems

Notes There are two basic types of predicates in LISP: Data-type predicates and equality predicates.
Data-type predicates take one argument and determine whether or not that argument qualifies
as the specified datatype. Here are some examples:
> (numberp 5)
T
> (numberp ‘FIVE)
NIL
> (stringp “hello, world”)
T
> (stringp 100)
NIL
“numberp” is a predicate function that returns T if the argument is a number, and NIL if it is not.
Likewise, “stringp” determines whether or not the argument is a string. Most data-type predicates
are written with the convention seen above; namely, the data-type name followed by a “p” for
predicate. The two common exceptions are “null” which determines whether or not an expression
evaluates to NIL, and “atom” which determines whether or not the argument is an atom (a
single value, indivisible into smaller parts...basically, not a list). Here are some common data-
type predicates built into the lisp language:
null
symbolp
atom
consp
listp
numberp
integerp
rationalp
floatp
complexp
characterp
stringp
vectorp
arrayp
functionp

Self Assessment

State whether the following statements are true or false:
9. The primary command for taking a list apart is the “Cdr” function.

10. Zero is the first element.
11. Most programs can be written without branching at some point.
12. Most data-type predicates are written with the convention.

4.4 Functions

LISP is a language that is usually associated with the “Functional Programming” paradigm. For
those of you who aren’t familiar with that term, functional programming takes a problem and
models it as mathematical functions for evaluation. This is in contrast to imperative programming
where “state” is the focus, and the outcome of a program is modeled in changes of state. As a
primarily-functional programming language, the most important building block of a LISP
program is the function, so here we’re going to talk about the specifics of defining new functions
and using them.

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