CLHS: Symbol DECLARE

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Symbol DECLARE

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 the next figure.

    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.

The next figure 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.)

Affected By: None.

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

Notes: None.

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

- DECLARE-FUNCTION-AMBIGUITY:DELETE-FTYPE-ABBREVIATION
- DYNAMIC-EXTENT:NEW-DECLARATION
- DECLARE-MACROS:FLUSH
- GENERIC-FLET-POORLY-DESIGNED:DELETE
- WITH-ADDED-METHODS:DELETE
- SYMBOL-MACROLET-DECLARE:ALLOW
- SETF-METHOD-VS-SETF-METHOD:RENAME-OLD-TERMS
- DECLS-AND-DOC

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