typep (ANSI and GNU Common Lisp Document)

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#### 4.4.28 typep [Function]

`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 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
    ;; 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 'A_x)

and

     (upgraded-array-element-type 'A_y)

denote the same type. Notice that

     (typep (make-array 0 :element-type 'A_x) '(array A_x)) ⇒  true
     (typep (make-array 0 :element-type 'A_y) '(array A_y)) ⇒  true
     (typep (make-array 0 :element-type 'A_x) '(array A_y)) ⇒  true
     (typep (make-array 0 :element-type 'A_y) '(array A_x)) ⇒  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 , 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.

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