[lisp] / mdw-base.lisp

;;; -*-lisp-*-
;;;
;;; $Id$
;;;
;;; Basic definitions
;;;
;;; (c) 2005 Mark Wooding
;;;

;;;----- Licensing notice ---------------------------------------------------
;;;
;;; This program is free software; you can redistribute it and/or modify
;;; it under the terms of the GNU General Public License as published by
;;; the Free Software Foundation; either version 2 of the License, or
;;; (at your option) any later version.
;;; 
;;; This program is distributed in the hope that it will be useful,
;;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
;;; GNU General Public License for more details.
;;; 
;;; You should have received a copy of the GNU General Public License
;;; along with this program; if not, write to the Free Software Foundation,
;;; Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.

;;;--------------------------------------------------------------------------
;;; Package things.

(defpackage #:mdw.base
  (:use #:common-lisp)
  (:export #:compile-time-defun
	   #:show
	   #:stringify #:listify #:fix-pair #:pairify
	   #:whitespace-char-p
	   #:slot-uninitialized
	   #:nlet #:while
	   #:with-gensyms #:let*/gensyms #:with-places
	   #:locp #:locf #:ref #:with-locatives
	   #:update-place #:update-place-after
	   #:incf-after #:decf-after))
(in-package #:mdw.base)

;;;--------------------------------------------------------------------------
;;; Some simple macros to get things going.

(defmacro compile-time-defun (name args &body body)
  "Define a function which can be used by macros during the compilation
process."
  `(eval-when (:compile-toplevel :load-toplevel)
     (defun ,name ,args ,@body)))

(defmacro show (x)
  "Debugging tool: print the expression X and its value."
  (let ((tmp (gensym)))
    `(let ((,tmp ,x))
       (format t "~&~S: ~S~%" ',x ,tmp)
       ,tmp)))

(defun stringify (str)
  "Return a string representation of STR.  Strings are returned unchanged;
symbols are converted to their names (unqualified!).  Other objects are
converted to their print representations."
  (typecase str
    (string str)
    (symbol (symbol-name str))
    (t (with-output-to-string (s)
	 (princ str s)))))

(compile-time-defun listify (x)
  "If X is a (possibly empty) list, return X; otherwise return (list X)."
  (if (listp x) x (list x)))

(compile-time-defun do-fix-pair (x y defaultp)
  "Helper function for fix-pair and pairify."
  (flet ((singleton (x) (values x (if defaultp y x))))
    (cond ((atom x) (singleton x))
	  ((null (cdr x)) (singleton (car x)))
	  ((atom (cdr x)) (values (car x) (cdr x)))
	  ((cddr x) (error "Too many elements for a pair."))
	  (t (values (car x) (cadr x))))))

(compile-time-defun fix-pair (x &optional (y nil defaultp))
  "Return two values extracted from X.  It works as follows:
  (A) -> A, Y
  (A B) -> A, B
  (A B . C) -> error
  (A . B) -> A, B
  A -> A, Y
where Y defaults to A if not specified."
  (do-fix-pair x y defaultp))

(compile-time-defun pairify (x &optional (y nil defaultp))
  "As for fix-pair, but returns a list instead of two values."
  (multiple-value-call #'list (do-fix-pair x y defaultp)))

(defun whitespace-char-p (ch)
  "Return whether CH is a whitespace character or not."
  (case ch
    ((#\space #\tab #\newline #\return #\vt #\formfeed) t)
    (t nil)))

(declaim (ftype (function nil ()) slot-unitialized))
(defun slot-uninitialized ()
  "A function which signals an error.  Can be used as an initializer form in
structure definitions without doom ensuing."
  (error "No initializer for slot."))

;;;--------------------------------------------------------------------------
;;; Generating symbols.

(defmacro with-gensyms (syms &body body)
  "Everyone's favourite macro helper."
  `(let (,@(mapcar (lambda (sym) `(,sym (gensym ,(symbol-name sym))))
                   (listify syms)))
     ,@body))

(defmacro let*/gensyms (binds &body body)
  "A macro helper.  BINDS is a list of binding pairs (VAR VALUE), where VALUE
defaults to VAR.  The result is that BODY is evaluated in a context where
each VAR is bound to a gensym, and in the final expansion, each of those
gensyms will be bound to the corresponding VALUE."
  (labels ((more (binds)
             (let ((tmp (gensym "TMP")) (bind (car binds)))
               `((let ((,tmp ,(cadr bind))
                       (,(car bind) (gensym ,(symbol-name (car bind)))))
                   `(let ((,,(car bind) ,,tmp))
                      ,,@(if (cdr binds)
                             (more (cdr binds))
                             body)))))))
    (if (null binds)
        `(progn ,@body)
        (car (more (mapcar #'pairify (listify binds)))))))

;;;--------------------------------------------------------------------------
;;; Some simple yet useful control structures.

(defmacro nlet (name binds &body body)
  "Scheme's named let."
  (multiple-value-bind (vars vals)
      (loop for bind in binds
	    for (var val) = (pairify bind nil)
	    collect var into vars
	    collect val into vals
	    finally (return (values vars vals)))
    `(labels ((,name ,vars
	        ,@body))
       (,name ,@vals))))

(defmacro while (cond &body body)
  "If COND is false, evaluate to nil; otherwise evaluate BODY and try again."
  `(loop
     (unless ,cond (return))
     ,@body))

;;;--------------------------------------------------------------------------
;;; with-places

(defmacro %place-ref (getform setform newtmp)
  "Grim helper macro for with-places."
  (declare (ignore setform newtmp))
  getform)

(define-setf-expander %place-ref (getform setform newtmp)
  "Grim helper macro for with-places."
  (values nil nil newtmp setform getform))

(defmacro with-places ((&key environment) places &body body)
  "A hairy helper, for writing setf-like macros.  PLACES is a list of binding
pairs (VAR PLACE), where PLACE defaults to VAR.  The result is that BODY is
evaluated in a context where each VAR is bound to a gensym, and in the final
expansion, each of those gensyms will be bound to a symbol-macro capable of
reading or setting the value of the corresponding PLACE."
  (if (null places)
      `(progn ,@body)
      (let*/gensyms (environment)
        (labels
            ((more (places)
               (let ((place (car places)))
                 (with-gensyms (tmp valtmps valforms
                                    newtmps setform getform)
                   `((let ((,tmp ,(cadr place))
                           (,(car place)
                            (gensym ,(symbol-name (car place)))))
                       (multiple-value-bind
                           (,valtmps ,valforms
                            ,newtmps ,setform ,getform)
                           (get-setf-expansion ,tmp
                                               ,environment)
                         (list 'let*
                               (mapcar #'list ,valtmps ,valforms)
                               `(symbol-macrolet ((,,(car place)
                                                   (%place-ref ,,getform
                                                               ,,setform
                                                               ,,newtmps)))
                                  ,,@(if (cdr places)
                                         (more (cdr places))
                                         body))))))))))
          (car (more (mapcar #'pairify (listify places))))))))

;;;--------------------------------------------------------------------------
;;; Update-in-place macros built using with-places.

(defmacro update-place (op place arg &environment env)
  "Update PLACE with the value of OP PLACE ARG, returning the new value."
  (with-places (:environment env) (place)
    `(setf ,place (,op ,place ,arg))))

(defmacro update-place-after (op place arg &environment env)
  "Update PLACE with the value of OP PLACE ARG, returning the old value."
  (with-places (:environment env) (place)
    (with-gensyms (x)
      `(let ((,x ,place))
	 (setf ,place (,op ,x ,arg))
	 ,x))))

(defmacro incf-after (place &optional (by 1))
  "Increment PLACE by BY, returning the old value."
  `(update-place-after + ,place ,by))

(defmacro decf-after (place &optional (by 1))
  "Decrement PLACE by BY, returning the old value."
  `(update-place-after - ,place ,by))

;;;--------------------------------------------------------------------------
;;; Locatives.

(defstruct (loc (:predicate locp) (:constructor make-loc (reader writer)))
  "Locative data type.  See `locf' and `ref'."
  (reader (slot-uninitialized) :type function)
  (writer (slot-uninitialized) :type function))

(defmacro locf (place &environment env)
  "Slightly cheesy locatives.  (locf PLACE) returns an object which, using
the `ref' function, can be used to read or set the value of PLACE.  It's
cheesy because it uses closures rather than actually taking the address of
something.  Also, unlike Zetalisp, we don't overload `car' to do our dirty
work."
  (multiple-value-bind
      (valtmps valforms newtmps setform getform)
      (get-setf-expansion place env)
    `(let* (,@(mapcar #'list valtmps valforms))
       (make-loc (lambda () ,getform)
                 (lambda (,@newtmps) ,setform)))))

(declaim (inline loc (setf loc)))

(defun ref (loc)
  "Fetch the value referred to by a locative."
  (funcall (loc-reader loc)))

(defun (setf ref) (new loc)
  "Store a new value in the place referred to by a locative."
  (funcall (loc-writer loc) new))

(defmacro with-locatives (locs &body body)
  "LOCS is a list of items of the form (SYM [LOC-EXPR]), where SYM is a
symbol and LOC-EXPR evaluates to a locative.  If LOC-EXPR is omitted, it
defaults to SYM.  As an abbreviation for a common case, LOCS may be a symbol
instead of a list.  The BODY is evaluated in an environment where each SYM is
a symbol macro which expands to (ref LOC-EXPR) -- or, in fact, something
similar which doesn't break if LOC-EXPR has side-effects.  Thus, references,
including `setf' forms, fetch or modify the thing referred to by the
LOC-EXPR.  Useful for covering over where something uses a locative."
  (setf locs (mapcar #'pairify (listify locs)))
  (let ((tt (mapcar (lambda (l) (declare (ignore l)) (gensym)) locs))
	(ll (mapcar #'cadr locs))
	(ss (mapcar #'car locs)))
    `(let (,@(mapcar (lambda (tmp loc) `(,tmp ,loc)) tt ll))
       (symbol-macrolet (,@(mapcar (lambda (sym tmp)
				     `(,sym (ref ,tmp))) ss tt))
	 ,@body))))

;;;----- That's all, folks --------------------------------------------------
Commit	Line	Data
861345b4	1	;;; --lisp--
	2	;;;
	3	;;; $Id$
	4	;;;
	5	;;; Basic definitions
	6	;;;
	7	;;; (c) 2005 Mark Wooding
	8	;;;
	9
	10	;;;----- Licensing notice ---------------------------------------------------
	11	;;;
	12	;;; This program is free software; you can redistribute it and/or modify
	13	;;; it under the terms of the GNU General Public License as published by
	14	;;; the Free Software Foundation; either version 2 of the License, or
	15	;;; (at your option) any later version.
	16	;;;
	17	;;; This program is distributed in the hope that it will be useful,
	18	;;; but WITHOUT ANY WARRANTY; without even the implied warranty of
	19	;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
	20	;;; GNU General Public License for more details.
	21	;;;
	22	;;; You should have received a copy of the GNU General Public License
	23	;;; along with this program; if not, write to the Free Software Foundation,
	24	;;; Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
	25
02866e07 MW	26	;;;--------------------------------------------------------------------------
	27	;;; Package things.
	28
861345b4	29	(defpackage #:mdw.base
	30	(:use #:common-lisp)
	31	(:export #:compile-time-defun
	32	#:show
	33	#:stringify #:listify #:fix-pair #:pairify
	34	#:whitespace-char-p
	35	#:slot-uninitialized
0375133b	36	#:nlet #:while
861345b4	37	#:with-gensyms #:let*/gensyms #:with-places
e979e568 MW	38	#:locp #:locf #:ref #:with-locatives
	39	#:update-place #:update-place-after
	40	#:incf-after #:decf-after))
861345b4	41	(in-package #:mdw.base)
861345b4	42
02866e07 MW	43	;;;--------------------------------------------------------------------------
	44	;;; Some simple macros to get things going.
	45
861345b4	46	(defmacro compile-time-defun (name args &body body)
	47	"Define a function which can be used by macros during the compilation
	48	process."
	49	`(eval-when (:compile-toplevel :load-toplevel)
	50	(defun ,name ,args ,@body)))
	51
	52	(defmacro show (x)
	53	"Debugging tool: print the expression X and its value."
	54	(let ((tmp (gensym)))
	55	`(let ((,tmp ,x))
	56	(format t "~&~S: ~S~%" ',x ,tmp)
	57	,tmp)))
	58
	59	(defun stringify (str)
	60	"Return a string representation of STR. Strings are returned unchanged;
	61	symbols are converted to their names (unqualified!). Other objects are
	62	converted to their print representations."
	63	(typecase str
	64	(string str)
	65	(symbol (symbol-name str))
	66	(t (with-output-to-string (s)
	67	(princ str s)))))
02866e07	68
861345b4	69	(compile-time-defun listify (x)
	70	"If X is a (possibly empty) list, return X; otherwise return (list X)."
	71	(if (listp x) x (list x)))
02866e07	72
861345b4	73	(compile-time-defun do-fix-pair (x y defaultp)
	74	"Helper function for fix-pair and pairify."
	75	(flet ((singleton (x) (values x (if defaultp y x))))
	76	(cond ((atom x) (singleton x))
	77	((null (cdr x)) (singleton (car x)))
	78	((atom (cdr x)) (values (car x) (cdr x)))
	79	((cddr x) (error "Too many elements for a pair."))
	80	(t (values (car x) (cadr x))))))
02866e07	81
861345b4	82	(compile-time-defun fix-pair (x &optional (y nil defaultp))
	83	"Return two values extracted from X. It works as follows:
	84	(A) -> A, Y
	85	(A B) -> A, B
	86	(A B . C) -> error
	87	(A . B) -> A, B
	88	A -> A, Y
	89	where Y defaults to A if not specified."
	90	(do-fix-pair x y defaultp))
02866e07	91
861345b4	92	(compile-time-defun pairify (x &optional (y nil defaultp))
	93	"As for fix-pair, but returns a list instead of two values."
	94	(multiple-value-call #'list (do-fix-pair x y defaultp)))
	95
	96	(defun whitespace-char-p (ch)
	97	"Return whether CH is a whitespace character or not."
	98	(case ch
	99	((#\space #\tab #\newline #\return #\vt #\formfeed) t)
	100	(t nil)))
	101
	102	(declaim (ftype (function nil ()) slot-unitialized))
	103	(defun slot-uninitialized ()
	104	"A function which signals an error. Can be used as an initializer form in
	105	structure definitions without doom ensuing."
	106	(error "No initializer for slot."))
	107
02866e07 MW	108	;;;--------------------------------------------------------------------------
	109	;;; Generating symbols.
	110
861345b4	111	(defmacro with-gensyms (syms &body body)
	112	"Everyone's favourite macro helper."
	113	`(let (,@(mapcar (lambda (sym) `(,sym (gensym ,(symbol-name sym))))
	114	(listify syms)))
	115	,@body))
	116
	117	(defmacro let*/gensyms (binds &body body)
	118	"A macro helper. BINDS is a list of binding pairs (VAR VALUE), where VALUE
	119	defaults to VAR. The result is that BODY is evaluated in a context where
	120	each VAR is bound to a gensym, and in the final expansion, each of those
	121	gensyms will be bound to the corresponding VALUE."
	122	(labels ((more (binds)
	123	(let ((tmp (gensym "TMP")) (bind (car binds)))
	124	`((let ((,tmp ,(cadr bind))
	125	(,(car bind) (gensym ,(symbol-name (car bind)))))
	126	`(let ((,,(car bind) ,,tmp))
	127	,,@(if (cdr binds)
	128	(more (cdr binds))
	129	body)))))))
	130	(if (null binds)
	131	`(progn ,@body)
	132	(car (more (mapcar #'pairify (listify binds)))))))
	133
02866e07	134	;;;--------------------------------------------------------------------------
f2d46aaa MW	135	;;; Some simple yet useful control structures.
	136
	137	(defmacro nlet (name binds &body body)
	138	"Scheme's named let."
	139	(multiple-value-bind (vars vals)
	140	(loop for bind in binds
	141	for (var val) = (pairify bind nil)
	142	collect var into vars
	143	collect val into vals
	144	finally (return (values vars vals)))
	145	`(labels ((,name ,vars
	146	,@body))
	147	(,name ,@vals))))
	148
	149	(defmacro while (cond &body body)
	150	"If COND is false, evaluate to nil; otherwise evaluate BODY and try again."
	151	`(loop
93f04724	152	(unless ,cond (return))
f2d46aaa MW	153	,@body))
	154
	155	;;;--------------------------------------------------------------------------
02866e07 MW	156	;;; with-places
02866e07 MW	157
861345b4	158	(defmacro %place-ref (getform setform newtmp)
	159	"Grim helper macro for with-places."
	160	(declare (ignore setform newtmp))
	161	getform)
02866e07	162
861345b4	163	(define-setf-expander %place-ref (getform setform newtmp)
	164	"Grim helper macro for with-places."
	165	(values nil nil newtmp setform getform))
02866e07	166
861345b4	167	(defmacro with-places ((&key environment) places &body body)
	168	"A hairy helper, for writing setf-like macros. PLACES is a list of binding
	169	pairs (VAR PLACE), where PLACE defaults to VAR. The result is that BODY is
	170	evaluated in a context where each VAR is bound to a gensym, and in the final
	171	expansion, each of those gensyms will be bound to a symbol-macro capable of
	172	reading or setting the value of the corresponding PLACE."
	173	(if (null places)
	174	`(progn ,@body)
	175	(let*/gensyms (environment)
	176	(labels
	177	((more (places)
	178	(let ((place (car places)))
	179	(with-gensyms (tmp valtmps valforms
	180	newtmps setform getform)
	181	`((let ((,tmp ,(cadr place))
	182	(,(car place)
	183	(gensym ,(symbol-name (car place)))))
	184	(multiple-value-bind
	185	(,valtmps ,valforms
	186	,newtmps ,setform ,getform)
	187	(get-setf-expansion ,tmp
	188	,environment)
	189	(list 'let*
	190	(mapcar #'list ,valtmps ,valforms)
	191	`(symbol-macrolet ((,,(car place)
	192	(%place-ref ,,getform
	193	,,setform
	194	,,newtmps)))
	195	,,@(if (cdr places)
	196	(more (cdr places))
	197	body))))))))))
	198	(car (more (mapcar #'pairify (listify places))))))))
	199
02866e07 MW	200	;;;--------------------------------------------------------------------------
	201	;;; Update-in-place macros built using with-places.
	202
e979e568 MW	203	(defmacro update-place (op place arg &environment env)
	204	"Update PLACE with the value of OP PLACE ARG, returning the new value."
	205	(with-places (:environment env) (place)
	206	`(setf ,place (,op ,place ,arg))))
02866e07	207
e979e568 MW	208	(defmacro update-place-after (op place arg &environment env)
	209	"Update PLACE with the value of OP PLACE ARG, returning the old value."
	210	(with-places (:environment env) (place)
	211	(with-gensyms (x)
	212	`(let ((,x ,place))
02866e07 MW	213	(setf ,place (,op ,x ,arg))
	214	,x))))
	215
e979e568 MW	216	(defmacro incf-after (place &optional (by 1))
	217	"Increment PLACE by BY, returning the old value."
	218	`(update-place-after + ,place ,by))
02866e07	219
e979e568 MW	220	(defmacro decf-after (place &optional (by 1))
	221	"Decrement PLACE by BY, returning the old value."
	222	`(update-place-after - ,place ,by))
	223
02866e07 MW	224	;;;--------------------------------------------------------------------------
02866e07 MW	225	;;; Locatives.
e979e568	226
861345b4	227	(defstruct (loc (:predicate locp) (:constructor make-loc (reader writer)))
	228	"Locative data type. See `locf' and `ref'."
	229	(reader (slot-uninitialized) :type function)
	230	(writer (slot-uninitialized) :type function))
02866e07	231
861345b4	232	(defmacro locf (place &environment env)
	233	"Slightly cheesy locatives. (locf PLACE) returns an object which, using
	234	the `ref' function, can be used to read or set the value of PLACE. It's
	235	cheesy because it uses closures rather than actually taking the address of
	236	something. Also, unlike Zetalisp, we don't overload `car' to do our dirty
	237	work."
	238	(multiple-value-bind
	239	(valtmps valforms newtmps setform getform)
	240	(get-setf-expansion place env)
	241	`(let* (,@(mapcar #'list valtmps valforms))
	242	(make-loc (lambda () ,getform)
	243	(lambda (,@newtmps) ,setform)))))
02866e07	244
861345b4	245	(declaim (inline loc (setf loc)))
02866e07	246
861345b4	247	(defun ref (loc)
	248	"Fetch the value referred to by a locative."
	249	(funcall (loc-reader loc)))
02866e07	250
861345b4	251	(defun (setf ref) (new loc)
	252	"Store a new value in the place referred to by a locative."
	253	(funcall (loc-writer loc) new))
02866e07	254
861345b4	255	(defmacro with-locatives (locs &body body)
	256	"LOCS is a list of items of the form (SYM [LOC-EXPR]), where SYM is a
	257	symbol and LOC-EXPR evaluates to a locative. If LOC-EXPR is omitted, it
	258	defaults to SYM. As an abbreviation for a common case, LOCS may be a symbol
	259	instead of a list. The BODY is evaluated in an environment where each SYM is
	260	a symbol macro which expands to (ref LOC-EXPR) -- or, in fact, something
	261	similar which doesn't break if LOC-EXPR has side-effects. Thus, references,
	262	including `setf' forms, fetch or modify the thing referred to by the
	263	LOC-EXPR. Useful for covering over where something uses a locative."
	264	(setf locs (mapcar #'pairify (listify locs)))
	265	(let ((tt (mapcar (lambda (l) (declare (ignore l)) (gensym)) locs))
	266	(ll (mapcar #'cadr locs))
	267	(ss (mapcar #'car locs)))
	268	`(let (,@(mapcar (lambda (tmp loc) `(,tmp ,loc)) tt ll))
	269	(symbol-macrolet (,@(mapcar (lambda (sym tmp)
	270	`(,sym (ref ,tmp))) ss tt))
	271	,@body))))
	272
	273	;;;----- That's all, folks --------------------------------------------------