mdw@git.distorted.org.uk Git - lisp/blob - mdw-base.lisp

   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
  26 ;;;--------------------------------------------------------------------------
  27 ;;; Package things.
  28
  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
  36            #:nlet #:while #:case2 #:ecase2
  37            #:with-gensyms #:let*/gensyms #:with-places
  38            #:locp #:locf #:ref #:with-locatives
  39            #:update-place #:update-place-after
  40            #:incf-after #:decf-after))
  41 (in-package #:mdw.base)
  42
  43 ;;;--------------------------------------------------------------------------
  44 ;;; Some simple macros to get things going.
  45
  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)))))
  68
  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)))
  72
  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))))))
  81
  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))
  91
  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
 108 ;;;--------------------------------------------------------------------------
 109 ;;; Generating symbols.
 110
 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
 134 ;;;--------------------------------------------------------------------------
 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
 152      (unless ,cond (return))
 153      ,@body))
 154
 155 (compile-time-defun do-case2-like (kind vform clauses)
 156   "Helper function for `case2' and `ecase2'."
 157   (with-gensyms (scrutinee argument)
 158     `(multiple-value-bind (,scrutinee ,argument) ,vform
 159        (declare (ignorable ,argument))
 160        (,kind ,scrutinee
 161          ,@(mapcar (lambda (clause)
 162                      (destructuring-bind
 163                          (cases (&optional var) &rest forms)
 164                          clause
 165                        `(,cases
 166                          ,@(if var
 167                                (list `(let ((,var ,argument)) ,@forms))
 168                                forms))))
 169                    clauses)))))
 170
 171 (defmacro case2 (vform &body clauses)
 172   "VFORM is a form which evaluates to two values, SCRUTINEE and ARGUMENT.
 173 The CLAUSES have the form (CASES ([VAR]) FORMS...), where a standard `case'
 174 clause has the form (CASES FORMS...).  The `case2' form evaluates the VFORM,
 175 and compares the SCRUTINEE to the various CASES, in order, just like `case'.
 176 If there is a match, then the corresponding FORMs are evaluated with VAR (if
 177 specified) bound to the value of ARGUMENT."
 178   (do-case2-like 'case vform clauses))
 179
 180 (defmacro ecase2 (vform &body clauses)
 181   "Like `case2', but signals an error if no clause matches the SCRUTINEE."
 182   (do-case2-like 'ecase vform clauses))
 183
 184 ;;;--------------------------------------------------------------------------
 185 ;;; with-places
 186
 187 (defmacro %place-ref (getform setform newtmp)
 188   "Grim helper macro for with-places."
 189   (declare (ignore setform newtmp))
 190   getform)
 191
 192 (define-setf-expander %place-ref (getform setform newtmp)
 193   "Grim helper macro for with-places."
 194   (values nil nil newtmp setform getform))
 195
 196 (defmacro with-places ((&key environment) places &body body)
 197   "A hairy helper, for writing setf-like macros.  PLACES is a list of binding
 198 pairs (VAR PLACE), where PLACE defaults to VAR.  The result is that BODY is
 199 evaluated in a context where each VAR is bound to a gensym, and in the final
 200 expansion, each of those gensyms will be bound to a symbol-macro capable of
 201 reading or setting the value of the corresponding PLACE."
 202   (if (null places)
 203       `(progn ,@body)
 204       (let*/gensyms (environment)
 205         (labels
 206             ((more (places)
 207                (let ((place (car places)))
 208                  (with-gensyms (tmp valtmps valforms
 209                                     newtmps setform getform)
 210                    `((let ((,tmp ,(cadr place))
 211                            (,(car place)
 212                             (gensym ,(symbol-name (car place)))))
 213                        (multiple-value-bind
 214                            (,valtmps ,valforms
 215                             ,newtmps ,setform ,getform)
 216                            (get-setf-expansion ,tmp
 217                                                ,environment)
 218                          (list 'let*
 219                                (mapcar #'list ,valtmps ,valforms)
 220                                `(symbol-macrolet ((,,(car place)
 221                                                    (%place-ref ,,getform
 222                                                                ,,setform
 223                                                                ,,newtmps)))
 224                                   ,,@(if (cdr places)
 225                                          (more (cdr places))
 226                                          body))))))))))
 227           (car (more (mapcar #'pairify (listify places))))))))
 228
 229 ;;;--------------------------------------------------------------------------
 230 ;;; Update-in-place macros built using with-places.
 231
 232 (defmacro update-place (op place arg &environment env)
 233   "Update PLACE with the value of OP PLACE ARG, returning the new value."
 234   (with-places (:environment env) (place)
 235     `(setf ,place (,op ,place ,arg))))
 236
 237 (defmacro update-place-after (op place arg &environment env)
 238   "Update PLACE with the value of OP PLACE ARG, returning the old value."
 239   (with-places (:environment env) (place)
 240     (with-gensyms (x)
 241       `(let ((,x ,place))
 242          (setf ,place (,op ,x ,arg))
 243          ,x))))
 244
 245 (defmacro incf-after (place &optional (by 1))
 246   "Increment PLACE by BY, returning the old value."
 247   `(update-place-after + ,place ,by))
 248
 249 (defmacro decf-after (place &optional (by 1))
 250   "Decrement PLACE by BY, returning the old value."
 251   `(update-place-after - ,place ,by))
 252
 253 ;;;--------------------------------------------------------------------------
 254 ;;; Locatives.
 255
 256 (defstruct (loc (:predicate locp) (:constructor make-loc (reader writer)))
 257   "Locative data type.  See `locf' and `ref'."
 258   (reader (slot-uninitialized) :type function)
 259   (writer (slot-uninitialized) :type function))
 260
 261 (defmacro locf (place &environment env)
 262   "Slightly cheesy locatives.  (locf PLACE) returns an object which, using
 263 the `ref' function, can be used to read or set the value of PLACE.  It's
 264 cheesy because it uses closures rather than actually taking the address of
 265 something.  Also, unlike Zetalisp, we don't overload `car' to do our dirty
 266 work."
 267   (multiple-value-bind
 268       (valtmps valforms newtmps setform getform)
 269       (get-setf-expansion place env)
 270     `(let* (,@(mapcar #'list valtmps valforms))
 271        (make-loc (lambda () ,getform)
 272                  (lambda (,@newtmps) ,setform)))))
 273
 274 (declaim (inline loc (setf loc)))
 275
 276 (defun ref (loc)
 277   "Fetch the value referred to by a locative."
 278   (funcall (loc-reader loc)))
 279
 280 (defun (setf ref) (new loc)
 281   "Store a new value in the place referred to by a locative."
 282   (funcall (loc-writer loc) new))
 283
 284 (defmacro with-locatives (locs &body body)
 285   "LOCS is a list of items of the form (SYM [LOC-EXPR]), where SYM is a
 286 symbol and LOC-EXPR evaluates to a locative.  If LOC-EXPR is omitted, it
 287 defaults to SYM.  As an abbreviation for a common case, LOCS may be a symbol
 288 instead of a list.  The BODY is evaluated in an environment where each SYM is
 289 a symbol macro which expands to (ref LOC-EXPR) -- or, in fact, something
 290 similar which doesn't break if LOC-EXPR has side-effects.  Thus, references,
 291 including `setf' forms, fetch or modify the thing referred to by the
 292 LOC-EXPR.  Useful for covering over where something uses a locative."
 293   (setf locs (mapcar #'pairify (listify locs)))
 294   (let ((tt (mapcar (lambda (l) (declare (ignore l)) (gensym)) locs))
 295         (ll (mapcar #'cadr locs))
 296         (ss (mapcar #'car locs)))
 297     `(let (,@(mapcar (lambda (tmp loc) `(,tmp ,loc)) tt ll))
 298        (symbol-macrolet (,@(mapcar (lambda (sym tmp)
 299                                      `(,sym (ref ,tmp))) ss tt))
 300          ,@body))))
 301
 302 ;;;----- That's all, folks --------------------------------------------------