CLHS: Function TYPEP

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Function TYPEP

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 `A`x`` and `A`y`` 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

Affected By: None.

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.

The following X3J13 cleanup issues, not part of the specification, apply to this section:

- ARRAY-TYPE-ELEMENT-TYPE-SEMANTICS:UNIFY-UPGRADING
- FUNCTION-TYPE
- SUBTYPEP-ENVIRONMENT:ADD-ARG

Copyright 1996-2005, LispWorks Ltd. All rights reserved.