CLHS: Function FUNCTION-LAMBDA-EXPRESSION

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Function FUNCTION-LAMBDA-EXPRESSION

Syntax:

function-lambda-expression function

=> lambda-expression, closure-p, name

Arguments and Values:

function---a function.

lambda-expression---a lambda expression or nil.

closure-p---a generalized boolean.

name---an object.

Description:

Returns information about function as follows:

The primary value, lambda-expression, is function's defining lambda expression, or nil if the information is not available. The lambda expression may have been pre-processed in some ways, but it should remain a suitable argument to compile or function. Any implementation may legitimately return nil as the lambda-expression of any function.

The secondary value, closure-p, is nil if function's definition was enclosed in the null lexical environment or something non-nil if function's definition might have been enclosed in some non-null lexical environment. Any implementation may legitimately return true as the closure-p of any function.

The tertiary value, name, is the ``name'' of function. The name is intended for debugging only and is not necessarily one that would be valid for use as a name in defun or function, for example. By convention, nil is used to mean that function has no name. Any implementation may legitimately return nil as the name of any function.

Examples:

The following examples illustrate some possible return values, but are not intended to be exhaustive:

     (function-lambda-expression #'(lambda (x) x))
    =>  NIL, false, NIL
    OR=>  NIL, true, NIL
    OR=>  (LAMBDA (X) X), true, NIL
    OR=>  (LAMBDA (X) X), false, NIL

     (function-lambda-expression
        (funcall #'(lambda () #'(lambda (x) x))))
    =>  NIL, false, NIL
    OR=>  NIL, true, NIL
    OR=>  (LAMBDA (X) X), true, NIL
    OR=>  (LAMBDA (X) X), false, NIL

     (function-lambda-expression
        (funcall #'(lambda (x) #'(lambda () x)) nil))
    =>  NIL, true, NIL
    OR=>  (LAMBDA () X), true, NIL
    NOT=>  NIL, false, NIL
    NOT=>  (LAMBDA () X), false, NIL

     (flet ((foo (x) x))
       (setf (symbol-function 'bar) #'foo)
       (function-lambda-expression #'bar))
    =>  NIL, false, NIL
    OR=>  NIL, true, NIL
    OR=>  (LAMBDA (X) (BLOCK FOO X)), true, NIL
    OR=>  (LAMBDA (X) (BLOCK FOO X)), false, FOO
    OR=>  (SI::BLOCK-LAMBDA FOO (X) X), false, FOO

     (defun foo ()
       (flet ((bar (x) x))
         #'bar))
     (function-lambda-expression (foo))
    =>  NIL, false, NIL
    OR=>  NIL, true, NIL
    OR=>  (LAMBDA (X) (BLOCK BAR X)), true, NIL
    OR=>  (LAMBDA (X) (BLOCK BAR X)), true, (:INTERNAL FOO 0 BAR)
    OR=>  (LAMBDA (X) (BLOCK BAR X)), false, "BAR in FOO"

Side Effects: None.

Affected By: None.

Exceptional Situations: None.

See Also: None.

Notes:

Although implementations are free to return ``nil, true, nil'' in all cases, they are encouraged to return a lambda expression as the primary value in the case where the argument was created by a call to compile or eval (as opposed to being created by loading a compiled file).

The following X3J13 cleanup issue, not part of the specification, applies to this section:

- FUNCTION-DEFINITION:JAN89-X3J13

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