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; Written by Matt Kaufmann, 2/27/09
; License: A 3-clause BSD license. See the LICENSE file distributed with ACL2.
; defmac.lisp
; Automated support for faster macroexpansion
(in-package "ACL2")
(include-book "xdoc/top" :dir :system)
(defxdoc defmac
:parents (defmacro)
:short "Define a macro that expands efficiently."
:long "<p>Example forms</p>
@({
(include-book \"misc/defmac\" :dir :system)
(defmac my-xor (x y)
(list 'if x (list 'not y) y))
(defmac my-mac (x &optional (y '3 y-p))
`(list ,x ,y ,y-p))
(defmac one-of (x &rest rst)
:macro-fn one-of-function
\"stubbed-out :doc.\"
(declare (xargs :guard (symbol-listp rst)))
(cond ((null rst) nil)
(t (list 'or
(list 'eq x (list 'quote (car rst)))
(list* 'one-of x (cdr rst))))))~/
})
<p>General Form:</p>
@({
(defmac name macro-args
:macro-fn name-macro-fn ; optional
doc-string ; optional
dcl ... dcl ; optional
body)
})
<p>where @('name') is a new symbolic name (see @(see name)), @(see macro-args)
specifies the formals of the macro (see @(see macro-args) for a description),
and @('body') is a term. @(see Doc-string) is an optional @(see documentation)
string; see @(see doc-string). Each @('dcl') is an optional declaration as for
@(see defun) (see @(see declare)).</p>
<p>See @(see defmacro) for a discussion of @('defmacro'), which is the
traditional way of introducing macros. @('Defmac') is similar to @('defmacro')
except that the resulting macro may execute significantly more efficiently, as
explained below. You can use @('defmac') just as you would normally use
@('defmacro'), though your @('defmac') form should include the declaration
@('(declare (xargs :mode :program)) to be truly compatible with @('defmacro'),
which allows calls of @(':')@(see program) mode functions in its body.</p>
<p>A @('defmac') form generates the following form, which introduces a @(see
defun) and a @(see defmacro). Here we refer to the ``General Form'' above;
hence the @(':macro-fn'), @('doc-string'), and each @('dcl') are optional. The
@('doc-string') is as specified for @(see defmacro), and each @('dcl') is as
specified for @(see defun). @(':Macro-fn') specifies @('name-macro-fn') (used
below) as illustrated above, but if @(':macro-fn') is not specified then
@('name-macro-fn') is obtained by adding the suffix @('\"-MACRO-FN\"') to the
@(see symbol-name) of @('name') to get a symbol in the same package as
@('name'). The list @('(v1 ... vk)') enumerates all the names introduced in
@('macro-args').</p>
@({
(progn
(defun name-macro-fn (v1 ... vk)
dcl ... dcl
body)
(defmacro name macro-args
doc-string
(name-macro-fn v1 ... vk))
)
})
<p>The reason for introducing a @('defun') is efficiency. ACL2 expands a macro
call by running its own evaluator on the body of the macro, and this can be
relatively slow if that body is large. But with @('defmac'), the evaluator
call reduces quickly to a single raw Lisp call of the (executable counterpart
of) the auxiliary function on the actuals of the macro.</p>")
; See :doc defmac for information.
(defun defmac-fn (mdef)
; Some of the code for this function is adapted from code for defmacro-fn.
(declare (xargs :mode :program))
(let ((ctx (cons 'defmac (car mdef))))
(mv-let
(macro-fn mdef)
(cond ((and (true-listp mdef)
(<= 4 (length mdef))
(eq (nth 2 mdef) :MACRO-FN))
(mv (nth 3 mdef) (list* (nth 0 mdef)
(nth 1 mdef)
(nthcdr 4 mdef))))
(t (mv nil mdef)))
(mv-let
(er-string four)
(chk-defmacro-width mdef)
(cond
(er-string (list 'er 'soft (kwote ctx) (kwote er-string) (kwote four)))
(t
(let ((name (car four))
(args (cadr four))
(dcls (caddr four))
(body (cadddr four)))
(cond
((or (not (symbolp name))
(keywordp name))
`(er soft ',ctx
"Names of macros must be non-keyword symbols. The name ~x0 ~
is thus illegal."
',name))
(t (let ((msg
; We need to check the shape of args before we can apply macro-vars (below).
(chk-macro-arglist-msg args nil nil)))
(cond (msg `(er soft ',ctx "~@0" ',msg))
(t
(let ((doc (if (stringp (car dcls)) (car dcls) nil))
(dcls (if (stringp (car dcls)) (cdr dcls) dcls))
(macro-fn (or macro-fn
(intern-in-package-of-symbol
(concatenate 'string
(symbol-name name)
"-MACRO-FN")
name)))
(formals (macro-vars args)))
`(progn (defun ,macro-fn ,formals
,@dcls
,body)
(defmacro ,name ,args
,@(and doc (list doc))
(,macro-fn ,@formals))))))))))))))))
(defmacro defmac (&rest mdef)
; The documentation below borrows heavily from :doc defmacro.
; Warning: See the Important Boot-Strapping Invariants before modifying!
(defmac-fn mdef))
; Example:
(local
(encapsulate
()
(defmac one-of (x &rest rst)
:macro-fn one-of-function
;; Jared removed the doc section here toward axing legacy doc stuff
"
stubbed-out :doc~/
~/~/"
(declare (xargs :guard (symbol-listp rst)))
(cond ((null rst) nil)
(t (list 'or
(list 'eq x (list 'quote (car rst)))
(list* 'one-of x (cdr rst))))))
(defun one-of-test-fn (a)
(one-of a u v w))
(defthm one-of-test-thm
(iff (one-of-test-fn a)
(member a '(u v w))))))
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