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  ANSI Common Lisp   4 Types and Classes   4.4 Dictionary of Types and Classes

4.4.28 typep Function

Syntax:
typep object type-specifier &optional environment    generalized-boolean

Arguments and Values:
object - an object.

type-specifier - any type specifier except values, or a type specifier list whose first element is either function or values.

environment - an environment object. The default is nil, denoting the null lexical environment and the and current global environment.

generalized-boolean - a generalized boolean.

Description:
Returns true if object is of the type specified by type-specifier; otherwise, returns false.

A type-specifier of the form (satisfies fn) is handled by applying the function fn to object.

(typep object '(array type-specifier)), where type-specifier is not *, returns true if and only if object is an array that could be the result of supplying type-specifier as the :element-type argument to make-array. (array *) refers to all arrays regardless of element type, while (array type-specifier) refers only to those arrays that can result from giving type-specifier as the :element-type argument to make-array. A similar interpretation applies to (simple-array type-specifier) and (vector type-specifier). See Section 15.1.2.1 Array Upgrading.

(typep object '(complex type-specifier)) returns true for all complex numbers that can result from giving numbers of type type-specifier to the function complex, plus all other complex numbers of the same specialized representation. Both the real and the imaginary parts of any such complex number must satisfy:

 (typep realpart 'type-specifier)









 (typep imagpart 'type-specifier)

See the function upgraded-complex-part-type.

Examples:
 (typep 12 'integer)  true
 (typep (1+ most-positive-fixnum) 'fixnum)  false
 (typep nil t)  true
 (typep nil nil)  false
 (typep 1 '(mod 2))  true
 (typep #c(1 1) '(complex (eql 1)))  true
;; To understand this next example, you might need to refer to
;; Section 12.1.5.3 Rule of Canonical Representation for Complex Rationals.
 (typep #c(0 0) '(complex (eql 0)))  false

Let Ax and Ay be two type specifiers that denote different types, but for which

 (upgraded-array-element-type 'Ax)
and

 (upgraded-array-element-type 'Ay)
denote the same type. Notice that

 (typep (make-array 0 :element-type 'Ax) '(array Ax))  true
 (typep (make-array 0 :element-type 'Ay) '(array Ay))  true
 (typep (make-array 0 :element-type 'Ax) '(array Ay))  true
 (typep (make-array 0 :element-type 'Ay) '(array Ax))  true

Exceptional Situations:
An error of type error is signaled if type-specifier is values, or a type specifier list whose first element is either function or values.

The consequences are undefined if the type-specifier is not a type specifier.

See Also:
type-of, upgraded-array-element-type, upgraded-complex-part-type, Section 4.2.3 Type Specifiers

Notes:
Implementations are encouraged to recognize and optimize the case of (typep x (the class y)), since it does not involve any need for expansion of deftype information at runtime.


Allegro CL Implementation Details:
None.

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