**●语法设定:**

**macroexpand** *form &optional env* =>

**macroexpand-1** *form &optional env* =>

**●参数和值:**

*form*---a *form*.

*env*---an *environment* *object*. The default is **nil**.

*expansion*---a *form*.

*expanded-p*---a *generalized boolean*.

**●详情:**

**macroexpand** and **macroexpand-1** expand *macros*.

If *form* is a *macro form*, then **macroexpand-1** expands the *macro form* call once.

**macroexpand** repeatedly expands *form* until it is no longer a *macro form*. In effect, **macroexpand** calls **macroexpand-1** repeatedly until the *secondary value* it returns is **nil**.

If *form* is a *macro form*, then the *expansion* is a *macro expansion* and *expanded-p* is *true*. Otherwise, the *expansion* is the given *form* and *expanded-p* is *false*.

Macro expansion is carried out as follows. Once **macroexpand-1** has determined that the *form* is a *macro form*, it obtains an appropriate expansion *function* for the *macro* or *symbol macro*. The value of ***macroexpand-hook*** is coerced to a *function* and then called as a *function* of three arguments: the expansion *function*, the *form*, and the *env*. The *value* returned from this call is taken to be the expansion of the
*form*.

In addition to *macro* definitions in the global environment, any local macro definitions established within *env* by **macrolet** or **symbol-macrolet** are considered. If only *form* is supplied as an argument, then the environment is effectively null, and only global macro definitions as established by **defmacro** are considered. *Macro* definitions are shadowed by local *function* definitions.

**●例子:**

(defmacro alpha (x y) `(beta ,x ,y)) => ALPHA (defmacro beta (x y) `(gamma ,x ,y)) => BETA (defmacro delta (x y) `(gamma ,x ,y)) => EPSILON (defmacro expand (form &environment env) (multiple-value-bind (expansion expanded-p) (macroexpand form env) `(values ',expansion ',expanded-p))) => EXPAND (defmacro expand-1 (form &environment env) (multiple-value-bind (expansion expanded-p) (macroexpand-1 form env) `(values ',expansion ',expanded-p))) => EXPAND-1 ;; Simple examples involving just the global environment (macroexpand-1 '(alpha a b)) => (BETA A B), true (expand-1 (alpha a b)) => (BETA A B), true (macroexpand '(alpha a b)) => (GAMMA A B), true (expand (alpha a b)) => (GAMMA A B), true (macroexpand-1 'not-a-macro) => NOT-A-MACRO, false (expand-1 not-a-macro) => NOT-A-MACRO, false (macroexpand '(not-a-macro a b)) => (NOT-A-MACRO A B), false (expand (not-a-macro a b)) => (NOT-A-MACRO A B), false ;; Examples involving lexical environments (macrolet ((alpha (x y) `(delta ,x ,y))) (macroexpand-1 '(alpha a b))) => (BETA A B), true (macrolet ((alpha (x y) `(delta ,x ,y))) (expand-1 (alpha a b))) => (DELTA A B), true (macrolet ((alpha (x y) `(delta ,x ,y))) (macroexpand '(alpha a b))) => (GAMMA A B), true (macrolet ((alpha (x y) `(delta ,x ,y))) (expand (alpha a b))) => (GAMMA A B), true (macrolet ((beta (x y) `(epsilon ,x ,y))) (expand (alpha a b))) => (EPSILON A B), true (let ((x (list 1 2 3))) (symbol-macrolet ((a (first x))) (expand a))) => (FIRST X), true (let ((x (list 1 2 3))) (symbol-macrolet ((a (first x))) (macroexpand 'a))) => A, false (symbol-macrolet ((b (alpha x y))) (expand-1 b)) => (ALPHA X Y), true (symbol-macrolet ((b (alpha x y))) (expand b)) => (GAMMA X Y), true (symbol-macrolet ((b (alpha x y)) (a b)) (expand-1 a)) => B, true (symbol-macrolet ((b (alpha x y)) (a b)) (expand a)) => (GAMMA X Y), true ;; Examples of shadowing behavior (flet ((beta (x y) (+ x y))) (expand (alpha a b))) => (BETA A B), true (macrolet ((alpha (x y) `(delta ,x ,y))) (flet ((alpha (x y) (+ x y))) (expand (alpha a b)))) => (ALPHA A B), false (let ((x (list 1 2 3))) (symbol-macrolet ((a (first x))) (let ((a x)) (expand a)))) => A, false

**●受制于:**

**defmacro**, **setf** of **macro-function**, **macrolet**, **symbol-macrolet**

**●例外情况：** 无。

**●更多信息:**

***macroexpand-hook***, **defmacro**, **setf** of **macro-function**, **macrolet**, **symbol-macrolet**, Section 3.1 (Evaluation)

**●说明:**

Neither **macroexpand** nor **macroexpand-1** makes any explicit attempt to expand *macro forms* that are either *subforms* of the *form* or
*subforms* of the *expansion*. Such expansion might occur implicitly, however, due to the semantics or implementation of the *macro function*.

X3J13设计清单

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