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   #+cmu (:import-from #:extensions #:fixnump))
  32
  33 (in-package #:mdw.base)
  34
  35 ;;;--------------------------------------------------------------------------
  36 ;;; Useful types.
  37
  38 (export 'unsigned-fixnum)
  39 (deftype unsigned-fixnum ()
  40   "Unsigned fixnums; useful as array indices and suchlike."
  41   `(mod ,most-positive-fixnum))
  42
  43 ;;;--------------------------------------------------------------------------
  44 ;;; Some simple macros to get things going.
  45
  46 (export 'compile-time-defun)
  47 (defmacro compile-time-defun (name args &body body)
  48   "Define a function which can be used by macros during the compilation
  49    process."
  50   `(eval-when (:compile-toplevel :load-toplevel :execute)
  51      (defun ,name ,args ,@body)))
  52
  53 (export 'show)
  54 (defmacro show (x)
  55   "Debugging tool: print the expression X and its values."
  56   (let ((tmp (gensym)))
  57     `(let ((,tmp (multiple-value-list ,x)))
  58        (fresh-line)
  59        (pprint-logical-block (*standard-output* nil :per-line-prefix ";; ")
  60          (format t
  61                  "~S = ~@_~:I~:[#<no values>~;~:*~{~S~^ ~_~}~]"
  62                  ',x
  63                  ,tmp))
  64        (terpri)
  65        (values-list ,tmp))))
  66
  67 (export 'stringify)
  68 (defun stringify (str)
  69   "Return a string representation of STR.  Strings are returned unchanged;
  70    symbols are converted to their names (unqualified!).  Other objects are
  71    converted to their print representations."
  72   (typecase str
  73     (string str)
  74     (symbol (symbol-name str))
  75     (t (princ-to-string str))))
  76
  77 (export 'functionify)
  78 (defun functionify (func)
  79   "Convert the function-designator FUNC to a function."
  80   (declare (type (or function symbol) func))
  81   (etypecase func
  82     (function func)
  83     (symbol (symbol-function func))))
  84
  85 (export 'mappend)
  86 (defun mappend (function list &rest more-lists)
  87   "Apply FUNCTION to corresponding elements of LIST and MORE-LISTS, yielding
  88    a list.  Return the concatenation of all the resulting lists.  Like
  89    mapcan, but nondestructive."
  90   (apply #'append (apply #'mapcar function list more-lists)))
  91
  92 (export 'listify)
  93 (compile-time-defun listify (x)
  94   "If X is a (possibly empty) list, return X; otherwise return (list X)."
  95   (if (listp x) x (list x)))
  96
  97 (compile-time-defun do-fix-pair (x y defaultp)
  98   "Helper function for fix-pair and pairify."
  99   (flet ((singleton (x) (values x (if defaultp y x))))
 100     (cond ((atom x) (singleton x))
 101           ((null (cdr x)) (singleton (car x)))
 102           ((atom (cdr x)) (values (car x) (cdr x)))
 103           ((cddr x) (error "Too many elements for a pair."))
 104           (t (values (car x) (cadr x))))))
 105
 106 (export 'fix-pair)
 107 (compile-time-defun fix-pair (x &optional (y nil defaultp))
 108   "Return two values extracted from X.  It works as follows:
 109      (A) -> A, Y
 110      (A B) -> A, B
 111      (A B . C) -> error
 112      (A . B) -> A, B
 113      A -> A, Y
 114    where Y defaults to A if not specified."
 115   (do-fix-pair x y defaultp))
 116
 117 (export 'pairify)
 118 (compile-time-defun pairify (x &optional (y nil defaultp))
 119   "As for fix-pair, but returns a list instead of two values."
 120   (multiple-value-call #'list (do-fix-pair x y defaultp)))
 121
 122 (export 'whitespace-char-p)
 123 (defun whitespace-char-p (ch)
 124   "Return whether CH is a whitespace character or not."
 125   (case ch
 126     (#.(loop for i below char-code-limit
 127              for ch = (code-char i)
 128              unless (with-input-from-string (in (string ch))
 129                       (peek-char t in nil))
 130              collect ch)
 131        t)
 132     (t nil)))
 133
 134 (export 'defconstant*)
 135 (defmacro defconstant* (name value &key doc test)
 136   "Define a constant, like `defconstant'.  The TEST is an equality test used
 137    to decide whether to override the current definition, if any."
 138   (let ((temp (gensym)))
 139     `(eval-when (:compile-toplevel :load-toplevel :execute)
 140        (let ((,temp ,value))
 141          (unless (and (boundp ',name)
 142                       (funcall ,(or test ''eql) (symbol-value ',name) ,temp))
 143            (defconstant ,name ,value ,@(and doc (list doc))))
 144          ',name))))
 145
 146 (export 'slot-uninitialized)
 147 (declaim (ftype (function nil ()) slot-unitialized))
 148 (defun slot-uninitialized ()
 149   "A function which signals an error.  Can be used as an initializer form in
 150    structure definitions without doom ensuing."
 151   (error "No initializer for slot."))
 152
 153 (export 'parse-body)
 154 (compile-time-defun parse-body (body &key (allow-docstring-p t))
 155   "Given a BODY (a list of forms), parses it into three sections: a
 156    docstring, a list of declarations (forms beginning with the symbol
 157    `declare') and the body forms.  The result is returned as three lists
 158    (even the docstring), suitable for interpolation into a backquoted list
 159    using `@,'.  If ALLOW-DOCSTRING-P is nil, docstrings aren't allowed at
 160    all."
 161   (let ((doc nil) (decls nil))
 162     (do ((forms body (cdr forms))) (nil)
 163       (let ((form (and forms (car forms))))
 164         (cond ((and allow-docstring-p (not doc) (stringp form) (cdr forms))
 165                (setf doc form))
 166               ((and (consp form)
 167                     (eq (car form) 'declare))
 168                (setf decls (append decls (cdr form))))
 169               (t (return (values (and doc (list doc))
 170                                  (and decls (list (cons 'declare decls)))
 171                                  forms))))))))
 172
 173 (export 'with-parsed-body)
 174 (defmacro with-parsed-body
 175     ((bodyvar declvar &optional (docvar (gensym) docp)) form &body body)
 176   "Parse FORM into a body, declarations and (maybe) a docstring; bind BODYVAR
 177    to the body, DECLVAR to the declarations, and DOCVAR to (a list
 178    containing) the docstring, and evaluate BODY."
 179   `(multiple-value-bind
 180        (,docvar ,declvar ,bodyvar)
 181        (parse-body ,form :allow-docstring-p ,docp)
 182      ,@(if docp nil `((declare (ignore ,docvar))))
 183      ,@body))
 184
 185 (export 'fixnump)
 186 #-cmu
 187 (progn
 188   (declaim (inline fixnump))
 189   (defun fixnump (object)
 190     "Answer non-nil if OBJECT is a fixnum, or nil if it isn't."
 191     (typep object 'fixnum)))
 192
 193 ;;;--------------------------------------------------------------------------
 194 ;;; Generating symbols.
 195
 196 (export 'with-gensyms)
 197 (defmacro with-gensyms (syms &body body)
 198   "Everyone's favourite macro helper."
 199   `(let (,@(mapcar (lambda (sym) `(,sym (gensym ,(symbol-name sym))))
 200                    (listify syms)))
 201      ,@body))
 202
 203 (export 'let*/gensyms)
 204 (defmacro let*/gensyms (binds &body body)
 205   "A macro helper.  BINDS is a list of binding pairs (VAR VALUE), where VALUE
 206    defaults to VAR.  The result is that BODY is evaluated in a context where
 207    each VAR is bound to a gensym, and in the final expansion, each of those
 208    gensyms will be bound to the corresponding VALUE."
 209   (labels ((more (binds)
 210              (let ((tmp (gensym "TMP")) (bind (car binds)))
 211                `((let ((,tmp ,(cadr bind))
 212                        (,(car bind) (gensym ,(symbol-name (car bind)))))
 213                    `(let ((,,(car bind) ,,tmp))
 214                       ,,@(if (cdr binds)
 215                              (more (cdr binds))
 216                              body)))))))
 217     (if (null binds)
 218         `(progn ,@body)
 219         (car (more (mapcar #'pairify (listify binds)))))))
 220
 221 ;;;--------------------------------------------------------------------------
 222 ;;; Capturing places as symbols.
 223
 224 (defmacro %place-ref (getform setform newtmp)
 225   "Grim helper macro for with-places."
 226   (declare (ignore setform newtmp))
 227   getform)
 228
 229 (define-setf-expander %place-ref (getform setform newtmp)
 230   "Grim helper macro for with-places."
 231   (values nil nil newtmp setform getform))
 232
 233 (export 'with-places)
 234 (defmacro with-places (clauses &body body &environment env)
 235   "Define symbols which refer to `setf'-able places.
 236
 237    The syntax is similar to `let'.  The CLAUSES are a list of (NAME PLACE)
 238    pairs.  Each NAME is defined as a symbol-macro referring to the
 239    corresponding PLACE: a mention of the NAME within the BODY forms extracts
 240    the current value(s) of the PLACE, while a `setf' (or `setq', because
 241    symbol macros are strange like that) of a NAME updates the value(s) in the
 242    PLACE.  The returned values are those of the BODY, evaluated as an
 243    implicit `progn'."
 244
 245   (let ((temp-binds nil)
 246         (macro-binds nil))
 247     (dolist (clause clauses)
 248       (destructuring-bind (name place) clause
 249         (multiple-value-bind (valtmps valforms newtmps setform getform)
 250             (get-setf-expansion place env)
 251           (setf temp-binds
 252                 (nconc (nreverse (mapcar #'list valtmps valforms))
 253                        temp-binds))
 254           (push `(,name (%place-ref ,getform ,setform ,newtmps))
 255                 macro-binds))))
 256     `(let (,@(nreverse temp-binds))
 257        (symbol-macrolet (,@(nreverse macro-binds))
 258          ,@body))))
 259
 260 (export 'with-places/gensyms)
 261 (defmacro with-places/gensyms (clauses &body body)
 262   "A kind of a cross between `with-places' and `let*/gensyms'.
 263
 264    This is a hairy helper for writing `setf'-like macros.  The CLAUSES are a
 265    list of (NAME [PLACE]) pairs, where the PLACE defaults to NAME, and a
 266    bare NAME may be written in place of the singleton list (NAME).  The
 267    PLACEs are evaluated.
 268
 269    The BODY forms are evaluated as an implicit `progn', with each NAME bound
 270    to a gensym, to produce a Lisp form, called the `kernel'.  The result of
 271    the `with-places/gensyms' macro is then itself a Lisp form, called the
 272    `result'.
 273
 274    The effect of evaluating the `result' form is to evaluate the `kernel'
 275    form with each of the gensyms stands for the value(s) stored in the
 276    corresponding PLACE; a `setf' (or `setq') of one of the gensyms updates
 277    the value(s) in the corresponding PLACE.  The values returned by the
 278    `result' form are the values returned by the `kernel'."
 279
 280   (let* ((clauses (mapcar #'pairify clauses))
 281          (names (mapcar #'car clauses))
 282          (places (mapcar #'cadr clauses))
 283          (gensyms (mapcar (lambda (name) (gensym (symbol-name name)))
 284                           names)))
 285     ``(with-places (,,@(mapcar (lambda (gensym place)
 286                                  ``(,',gensym ,,place))
 287                                gensyms places))
 288         ,(let (,@(mapcar (lambda (name gensym)
 289                            `(,name ',gensym))
 290                          names gensyms))
 291            ,@body))))
 292
 293 ;;;--------------------------------------------------------------------------
 294 ;;; Some simple yet useful control structures.
 295
 296 (export 'nlet)
 297 (defmacro nlet (name binds &body body)
 298   "Scheme's named let."
 299   (multiple-value-bind (vars vals)
 300       (loop for bind in binds
 301             for (var val) = (pairify bind nil)
 302             collect var into vars
 303             collect val into vals
 304             finally (return (values vars vals)))
 305     `(labels ((,name ,vars
 306                 ,@body))
 307        (,name ,@vals))))
 308
 309 (export 'while)
 310 (defmacro while (cond &body body)
 311   "If COND is false, evaluate to nil; otherwise evaluate BODY and try again."
 312   `(loop (unless ,cond (return)) (progn ,@body)))
 313
 314 (export 'until)
 315 (defmacro until (cond &body body)
 316   "If COND is true, evaluate to nil; otherwise evaluate BODY and try again."
 317   `(loop (when ,cond (return)) (progn ,@body)))
 318
 319 (compile-time-defun do-case2-like (kind vform clauses)
 320   "Helper function for `case2' and `ecase2'."
 321   (with-gensyms (scrutinee argument)
 322     `(multiple-value-bind (,scrutinee ,argument) ,vform
 323        (declare (ignorable ,argument))
 324        (,kind ,scrutinee
 325          ,@(mapcar (lambda (clause)
 326                      (destructuring-bind
 327                          (cases (&optional varx vary) &rest forms)
 328                          clause
 329                        `(,cases
 330                          ,@(if varx
 331                                (list `(let ((,(or vary varx) ,argument)
 332                                             ,@(and vary
 333                                                    `((,varx ,scrutinee))))
 334                                         ,@forms))
 335                                forms))))
 336                    clauses)))))
 337
 338 (export 'caase2)
 339 (defmacro case2 (vform &body clauses)
 340   "VFORM is a form which evaluates to two values, SCRUTINEE and ARGUMENT.
 341    The CLAUSES have the form (CASES ([[SCRUVAR] ARGVAR]) FORMS...), where a
 342    standard `case' clause has the form (CASES FORMS...).  The `case2' form
 343    evaluates the VFORM, and compares the SCRUTINEE to the various CASES, in
 344    order, just like `case'.  If there is a match, then the corresponding
 345    FORMs are evaluated with ARGVAR bound to the ARGUMENT and SCRUVAR bound to
 346    the SCRUTINEE (where specified).  Note the bizarre defaulting behaviour:
 347    ARGVAR is less optional than SCRUVAR."
 348   (do-case2-like 'case vform clauses))
 349
 350 (export 'ecase2)
 351 (defmacro ecase2 (vform &body clauses)
 352   "Like `case2', but signals an error if no clause matches the SCRUTINEE."
 353   (do-case2-like 'ecase vform clauses))
 354
 355 (export 'setf-default)
 356 (defmacro setf-default (&rest specs)
 357   "Like setf, but only sets places which are currently nil.
 358
 359    The arguments are an alternating list of PLACEs and DEFAULTs.  If a PLACE
 360    is nil, the DEFAULT is evaluated and stored in the PLACE; otherwise the
 361    default is /not/ stored.  The result is the (new) value of the last
 362    PLACE."
 363   `(progn ,@(do ((list nil)
 364                  (specs specs (cddr specs)))
 365                 ((endp specs) (nreverse list))
 366               (unless (cdr specs)
 367                 (error "Odd number of arguments for `setf-default'."))
 368               (push (with-places/gensyms ((place (car specs)))
 369                       `(or ,place (setf ,place ,(cadr specs))))
 370                     list))))
 371
 372 ;;;--------------------------------------------------------------------------
 373 ;;; Update-in-place macros built using with-places.
 374
 375 (export 'update-place)
 376 (defmacro update-place (op place &rest args)
 377   "Update PLACE with (OP PLACE . ARGS), returning the new value."
 378   (with-places/gensyms (place)
 379     `(setf ,place (,op ,place ,@args))))
 380
 381 (export 'update-place-after)
 382 (defmacro update-place-after (op place &rest args)
 383   "Update PLACE with (OP PLACE . ARGS), returning the old value."
 384   (with-places/gensyms (place)
 385     (with-gensyms (x)
 386       `(let ((,x ,place))
 387          (setf ,place (,op ,x ,@args))
 388          ,x))))
 389
 390 (export 'incf-after)
 391 (defmacro incf-after (place &optional (by 1))
 392   "Increment PLACE by BY, returning the old value."
 393   `(update-place-after + ,place ,by))
 394
 395 (export 'decf-after)
 396 (defmacro decf-after (place &optional (by 1))
 397   "Decrement PLACE by BY, returning the old value."
 398   `(update-place-after - ,place ,by))
 399
 400 ;;;--------------------------------------------------------------------------
 401 ;;; Locatives.
 402
 403 (export 'locp)
 404 (defstruct (loc (:predicate locp) (:constructor make-loc (reader writer)))
 405   "Locative data type.  See `locf' and `ref'."
 406   (reader (slot-uninitialized) :type function :read-only t)
 407   (writer (slot-uninitialized) :type function :read-only t))
 408
 409 (export 'locf)
 410 (defmacro locf (place &environment env)
 411   "Slightly cheesy locatives.  (locf PLACE) returns an object which, using
 412    the `ref' function, can be used to read or set the value of PLACE.  It's
 413    cheesy because it uses closures rather than actually taking the address of
 414    something.  Also, unlike Zetalisp, we don't overload `car' to do our dirty
 415    work."
 416   (multiple-value-bind
 417       (valtmps valforms newtmps setform getform)
 418       (get-setf-expansion place env)
 419     `(let* (,@(mapcar #'list valtmps valforms))
 420        (make-loc (lambda () ,getform)
 421                  (lambda (,@newtmps) ,setform)))))
 422
 423 (export 'ref)
 424 (declaim (inline ref (setf ref)))
 425 (defun ref (loc)
 426   "Fetch the value referred to by a locative."
 427   (funcall (loc-reader loc)))
 428 (defun (setf ref) (new loc)
 429   "Store a new value in the place referred to by a locative."
 430   (funcall (loc-writer loc) new))
 431
 432 (export 'with-locatives)
 433 (defmacro with-locatives (locs &body body)
 434   "LOCS is a list of items of the form (SYM [LOC-EXPR]), where SYM is a
 435    symbol and LOC-EXPR evaluates to a locative.  If LOC-EXPR is omitted, it
 436    defaults to SYM.  As an abbreviation for a common case, LOCS may be a
 437    symbol instead of a list.  The BODY is evaluated in an environment where
 438    each SYM is a symbol macro which expands to (ref LOC-EXPR) -- or, in fact,
 439    something similar which doesn't break if LOC-EXPR has side-effects.  Thus,
 440    references, including `setf' forms, fetch or modify the thing referred to
 441    by the LOC-EXPR.  Useful for covering over where something uses a
 442    locative."
 443   (setf locs (mapcar #'pairify (listify locs)))
 444   (let ((tt (mapcar (lambda (l) (declare (ignore l)) (gensym)) locs))
 445         (ll (mapcar #'cadr locs))
 446         (ss (mapcar #'car locs)))
 447     `(let (,@(mapcar (lambda (tmp loc) `(,tmp ,loc)) tt ll))
 448        (symbol-macrolet (,@(mapcar (lambda (sym tmp)
 449                                      `(,sym (ref ,tmp))) ss tt))
 450          ,@body))))
 451
 452 ;;;----- That's all, folks --------------------------------------------------