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  ANSI Common Lisp   3 Evaluation and Compilation   3.8 Dictionary Evaluation and Compilation

3.8.18 declare Symbol

declare {declaration-specifier}*

declaration-specifier - a declaration specifier; not evaluated.

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 the next figure.

Standardized Forms In Which Declarations Can Occur
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

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.

The next figure shows a list of declaration identifiers that can be used with declare.

Local Declaration Specifiers
dynamic-extent ignore optimize
ftype inline special
ignorable notinline type

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

 (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.

See Also:
proclaim, Section 4.2.3 Type Specifiers, declaration, dynamic-extent, ftype, ignorable, ignore, inline, notinline, optimize, type

Allegro CL Implementation Details:

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