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<span id="check_002dtype"></span><div class="header">
<p>
Next: <a href="simple_002derror.html" accesskey="n" rel="next">simple-error</a>, Previous: <a href="cerror.html" accesskey="p" rel="prev">cerror</a>, Up: <a href="Conditions-Dictionary.html" accesskey="u" rel="up">Conditions Dictionary</a> </p>
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<hr>
<span id="check_002dtype-_005bMacro_005d"></span><h4 class="subsection">9.2.13 check-type [Macro]</h4>
<p><code>check-type</code> <i>place typespec <span class="roman"><span class="roman">[</span><i>string</i><span class="roman">]</span></span></i> ⇒ <i><b>nil</b></i>
</p>
<span id="Arguments-and-Values_003a_003a-135"></span><h4 class="subsubheading">Arguments and Values::</h4>
<p><i>place</i>—a <i>place</i>.
</p>
<p><i>typespec</i>—a <i>type specifier</i>.
</p>
<p><i>string</i>—a <i>string</i>; evaluated.
</p>
<span id="Description_003a_003a-183"></span><h4 class="subsubheading">Description::</h4>
<p><b>check-type</b> signals a <i>correctable</i> <i>error</i>
of <i>type</i> <b>type-error</b> if the contents of <i>place</i> are not
of the type <i>typespec</i>.
</p>
<p><b>check-type</b> can return only if the <b>store-value</b> <i>restart</i> is invoked,
either explicitly from a handler
or implicitly as one of the options offered by the debugger.
If the <b>store-value</b> <i>restart</i> is invoked,
<b>check-type</b> stores the new value
that is the argument to the <i>restart</i> invocation
(or that is prompted for interactively by the debugger)
in <i>place</i> and starts over,
checking the type of the new value
and signaling another error if it is still not of the desired <i>type</i>.
</p>
<p>The first time <i>place</i> is <i>evaluated</i>,
it is <i>evaluated</i> by normal evaluation rules.
It is later <i>evaluated</i> as a <i>place</i>
if the type check fails and the <b>store-value</b> <i>restart</i> is used;
see <a href="Evaluation-of-Subforms-to-Places.html">Evaluation of Subforms to Places</a>.
</p>
<p><i>string</i> should be an English description of the type,
starting with an indefinite article (“a” or “an”).
If <i>string</i> is not supplied,
it is computed automatically from <i>typespec</i>.
The automatically generated message mentions
<i>place</i>,
its contents,
and the desired type.
An implementation may choose to generate
a somewhat differently worded error message
if it recognizes that <i>place</i> is of a particular form,
such as one of the arguments to the function that called <b>check-type</b>.
<i>string</i> is allowed because some applications of <b>check-type</b>
may require a more specific description of what is wanted
than can be generated automatically from <i>typespec</i>.
</p>
<span id="Examples_003a_003a-117"></span><h4 class="subsubheading">Examples::</h4>
<div class="example">
<pre class="example"> (setq aardvarks '(sam harry fred))
⇒ (SAM HARRY FRED)
(check-type aardvarks (array * (3)))
<tt> |> </tt> Error: The value of AARDVARKS, (SAM HARRY FRED),
<tt> |> </tt> is not a 3-long array.
<tt> |> </tt> To continue, type :CONTINUE followed by an option number:
<tt> |> </tt> 1: Specify a value to use instead.
<tt> |> </tt> 2: Return to Lisp Toplevel.
<tt> |> </tt> Debug> <b>|>></b><tt>:CONTINUE 1</tt><b><<|</b>
<tt> |> </tt> Use Value: <b>|>></b><tt>#(SAM FRED HARRY)</tt><b><<|</b>
⇒ NIL
aardvarks
⇒ #<ARRAY-T-3 13571>
(map 'list #'identity aardvarks)
⇒ (SAM FRED HARRY)
(setq aardvark-count 'foo)
⇒ FOO
(check-type aardvark-count (integer 0 *) "A positive integer")
<tt> |> </tt> Error: The value of AARDVARK-COUNT, FOO, is not a positive integer.
<tt> |> </tt> To continue, type :CONTINUE followed by an option number:
<tt> |> </tt> 1: Specify a value to use instead.
<tt> |> </tt> 2: Top level.
<tt> |> </tt> Debug> <b>|>></b><tt>:CONTINUE 2</tt><b><<|</b>
</pre></div>
<div class="example">
<pre class="example"> (defmacro define-adder (name amount)
(check-type name (and symbol (not null)) "a name for an adder function")
(check-type amount integer)
`(defun ,name (x) (+ x ,amount)))
(macroexpand '(define-adder add3 3))
⇒ (defun add3 (x) (+ x 3))
(macroexpand '(define-adder 7 7))
<tt> |> </tt> Error: The value of NAME, 7, is not a name for an adder function.
<tt> |> </tt> To continue, type :CONTINUE followed by an option number:
<tt> |> </tt> 1: Specify a value to use instead.
<tt> |> </tt> 2: Top level.
<tt> |> </tt> Debug> <b>|>></b><tt>:Continue 1</tt><b><<|</b>
<tt> |> </tt> Specify a value to use instead.
<tt> |> </tt> Type a form to be evaluated and used instead: <b>|>></b><tt>'ADD7</tt><b><<|</b>
⇒ (defun add7 (x) (+ x 7))
(macroexpand '(define-adder add5 something))
<tt> |> </tt> Error: The value of AMOUNT, SOMETHING, is not an integer.
<tt> |> </tt> To continue, type :CONTINUE followed by an option number:
<tt> |> </tt> 1: Specify a value to use instead.
<tt> |> </tt> 2: Top level.
<tt> |> </tt> Debug> <b>|>></b><tt>:Continue 1</tt><b><<|</b>
<tt> |> </tt> Type a form to be evaluated and used instead: <b>|>></b><tt>5</tt><b><<|</b>
⇒ (defun add5 (x) (+ x 5))
</pre></div>
<p>Control is transferred to a handler.
</p>
<span id="Side-Effects_003a_003a-9"></span><h4 class="subsubheading">Side Effects::</h4>
<p>The debugger might be entered.
</p>
<span id="Affected-By_003a_003a-21"></span><h4 class="subsubheading">Affected By::</h4>
<p><b>*break-on-signals*</b>
</p>
<p>The implementation.
</p>
<span id="See-Also_003a_003a-161"></span><h4 class="subsubheading">See Also::</h4>
<p><a href="Condition-System-Concepts.html">Condition System Concepts</a>
</p>
<span id="Notes_003a_003a-100"></span><h4 class="subsubheading">Notes::</h4>
<div class="example">
<pre class="example"> (check-type <i>place</i> <i>typespec</i>)
≡ (assert (typep <i>place</i> '<i>typespec</i>) (<i>place</i>)
'type-error :datum <i>place</i> :expected-type '<i>typespec</i>)
</pre></div>
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