declare (ANSI and GNU Common Lisp Document)

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#### 3.8.18 declare [Symbol]

#### Syntax::

`declare` {declaration-specifier}*

#### Arguments::

declaration-specifier—a declaration specifier; not evaluated.

#### Description::

A declare expression, sometimes called a declaration, can occur only at the beginning of the bodies of certain forms; that is, it may be preceded only by other declare expressions, or by a documentation string if the context permits.

A declare expression can occur in a lambda expression or in any of the forms listed in Figure 3–23.

      defgeneric                 do-external-symbols   prog
      define-compiler-macro      do-symbols            prog*
      define-method-combination  dolist                restart-case
      define-setf-expander       dotimes               symbol-macrolet
      defmacro                   flet                  with-accessors
      defmethod                  handler-case          with-hash-table-iterator
      defsetf                    labels                with-input-from-string
      deftype                    let                   with-open-file
      defun                      let*                  with-open-stream
      destructuring-bind         locally               with-output-to-string
      do                         macrolet              with-package-iterator
      do*                        multiple-value-bind   with-slots
      do-all-symbols             pprint-logical-block

           Figure 3–23: Standardized Forms In Which Declarations Can Occur

A declare expression can only occur where specified by the syntax of these forms. The consequences of attempting to evaluate a declare expression are undefined. In situations where such expressions can appear, explicit checks are made for their presence and they are never actually evaluated; it is for this reason that they are called “declare expressions” rather than “declare forms.”

Macro forms cannot expand into declarations; declare expressions must appear as actual subexpressions of the form to which they refer.

Figure 3–24 shows a list of declaration identifiers that can be used with declare.

      dynamic-extent  ignore     optimize
      ftype           inline     special
      ignorable       notinline  type

      Figure 3–24: Local Declaration Specifiers

An implementation is free to support other (implementation-defined) declaration identifiers as well.

#### Examples::

     (defun nonsense (k x z)
       (foo z x)                     ;First call to foo
       (let ((j (foo k x))           ;Second call to foo
             (x (* k k)))
         (declare (inline foo) (special x z))
         (foo x j z)))               ;Third call to foo

In this example, the inline declaration applies only to the third call to `foo`, but not to the first or second ones. The special declaration of `x` causes let to make a dynamic binding for `x`, and causes the reference to `x` in the body of let to be a dynamic reference. The reference to `x` in the second call to `foo` is a local reference to the second parameter of `nonsense`. The reference to `x` in the first call to `foo` is a local reference, not a special one. The special declaration of `z` causes the reference to `z` in the third call to `foo` to be a dynamic reference; it does not refer to the parameter to `nonsense` named `z`, because that parameter binding has not been declared to be special. (The special declaration of `z` does not appear in the body of defun, but in an inner form, and therefore does not affect the binding of the parameter.)

#### Exceptional Situations::

The consequences of trying to use a declare expression as a form to be evaluated are undefined.

[Editorial Note by KMP: Probably we need to say something here about ill-formed declare expressions.]

#### See Also::

proclaim , Type Specifiers, declaration, dynamic-extent, ftype, ignorable, ignore, inline, notinline, optimize, type

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