src/code/macroexpand.lisp

   1 ;;;; MACROEXPAND and friends
   2
   3 ;;;; This software is part of the SBCL system. See the README file for
   4 ;;;; more information.
   5 ;;;;
   6 ;;;; This software is derived from the CMU CL system, which was
   7 ;;;; written at Carnegie Mellon University and released into the
   8 ;;;; public domain. The software is in the public domain and is
   9 ;;;; provided with absolutely no warranty. See the COPYING and CREDITS
  10 ;;;; files for more information.
  11
  12 (in-package "SB!IMPL")
  13 \f
  14 ;;;; syntactic environment access
  15
  16 (defun sb!xc:special-operator-p (symbol)
  17   #!+sb-doc
  18   "If the symbol globally names a special form, return T, otherwise NIL."
  19   (declare (symbol symbol))
  20   (eq (info :function :kind symbol) :special-form))
  21
  22 (defvar sb!xc:*macroexpand-hook* 'funcall
  23   #!+sb-doc
  24   "The value of this variable must be a designator for a function that can
  25   take three arguments, a macro expander function, the macro form to be
  26   expanded, and the lexical environment to expand in. The function should
  27   return the expanded form. This function is called by MACROEXPAND-1
  28   whenever a runtime expansion is needed. Initially this is set to
  29   FUNCALL.")
  30
  31 (defun sb!xc:macroexpand-1 (form &optional env)
  32   #!+sb-doc
  33   "If form is a macro (or symbol macro), expand it once. Return two values,
  34    the expanded form and a T-or-NIL flag indicating whether the form was, in
  35    fact, a macro. ENV is the lexical environment to expand in, which defaults
  36    to the null environment."
  37   (cond ((and (consp form) (symbolp (car form)))
  38          (let ((def (sb!xc:macro-function (car form) env)))
  39            (if def
  40                (values (funcall sb!xc:*macroexpand-hook*
  41                                 def
  42                                 form
  43                                 ;; As far as I can tell, it's not clear from
  44                                 ;; the ANSI spec whether a MACRO-FUNCTION
  45                                 ;; function needs to be prepared to handle
  46                                 ;; NIL as a lexical environment. CMU CL
  47                                 ;; passed NIL through to the MACRO-FUNCTION
  48                                 ;; function, but I prefer SBCL "be conservative
  49                                 ;; in what it sends and liberal in what it
  50                                 ;; accepts" by doing the defaulting itself.
  51                                 ;; -- WHN 19991128
  52                                 (coerce-to-lexenv env))
  53                        t)
  54                (values form nil))))
  55         ((symbolp form)
  56          (flet ((perform-symbol-expansion (symbol expansion)
  57                   ;; CLHS 3.1.2.1.1 specifies that symbol-macros are expanded
  58                   ;; via the macroexpand hook, too.
  59                   (funcall sb!xc:*macroexpand-hook*
  60                            (constantly expansion)
  61                            symbol
  62                            env)))
  63            (let* ((venv (when env (sb!c::lexenv-vars env)))
  64                   (local-def (cdr (assoc form venv))))
  65              (cond ((and (consp local-def)
  66                          (eq (car local-def) 'macro))
  67                     (values (perform-symbol-expansion form (cdr local-def)) t))
  68                    (local-def
  69                     (values form nil))
  70                    ((eq (info :variable :kind form) :macro)
  71                     (let ((expansion (info :variable :macro-expansion form)))
  72                       (values (perform-symbol-expansion form expansion) t)))
  73                    (t
  74                     (values form nil))))))
  75         (t
  76          (values form nil))))
  77
  78 (defun sb!xc:macroexpand (form &optional env)
  79   #!+sb-doc
  80   "Repetitively call MACROEXPAND-1 until the form can no longer be expanded.
  81    Returns the final resultant form, and T if it was expanded. ENV is the
  82    lexical environment to expand in, or NIL (the default) for the null
  83    environment."
  84   (labels ((frob (form expanded)
  85              (multiple-value-bind (new-form newly-expanded-p)
  86                  (sb!xc:macroexpand-1 form env)
  87                (if newly-expanded-p
  88                    (frob new-form t)
  89                    (values new-form expanded)))))
  90     (frob form nil)))