libguile/promises.c

   1 /* Copyright (C) 1995,1996,1997,1998,1999,2000,2001,2002,2003,2004,2005,2006,2007,2008,2009
   2  * Free Software Foundation, Inc.
   3  *
   4  * This library is free software; you can redistribute it and/or
   5  * modify it under the terms of the GNU Lesser General Public License
   6  * as published by the Free Software Foundation; either version 3 of
   7  * the License, or (at your option) any later version.
   8  *
   9  * This library is distributed in the hope that it will be useful, but
  10  * WITHOUT ANY WARRANTY; without even the implied warranty of
  11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12  * Lesser General Public License for more details.
  13  *
  14  * You should have received a copy of the GNU Lesser General Public
  15  * License along with this library; if not, write to the Free Software
  16  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
  17  * 02110-1301 USA
  18  */
  19
  20 \f
  21
  22 #ifdef HAVE_CONFIG_H
  23 #  include <config.h>
  24 #endif
  25
  26 #include <alloca.h>
  27
  28 #include "libguile/__scm.h"
  29
  30 #include "libguile/_scm.h"
  31 #include "libguile/alist.h"
  32 #include "libguile/async.h"
  33 #include "libguile/continuations.h"
  34 #include "libguile/debug.h"
  35 #include "libguile/deprecation.h"
  36 #include "libguile/dynwind.h"
  37 #include "libguile/eq.h"
  38 #include "libguile/eval.h"
  39 #include "libguile/feature.h"
  40 #include "libguile/fluids.h"
  41 #include "libguile/goops.h"
  42 #include "libguile/hash.h"
  43 #include "libguile/hashtab.h"
  44 #include "libguile/lang.h"
  45 #include "libguile/list.h"
  46 #include "libguile/macros.h"
  47 #include "libguile/memoize.h"
  48 #include "libguile/modules.h"
  49 #include "libguile/ports.h"
  50 #include "libguile/print.h"
  51 #include "libguile/procprop.h"
  52 #include "libguile/programs.h"
  53 #include "libguile/root.h"
  54 #include "libguile/smob.h"
  55 #include "libguile/srcprop.h"
  56 #include "libguile/stackchk.h"
  57 #include "libguile/strings.h"
  58 #include "libguile/threads.h"
  59 #include "libguile/throw.h"
  60 #include "libguile/validate.h"
  61 #include "libguile/values.h"
  62 #include "libguile/promises.h"
  63
  64
  65 \f
  66
  67
  68 scm_t_bits scm_tc16_promise;
  69
  70 SCM_DEFINE (scm_make_promise, "make-promise", 1, 0, 0,
  71             (SCM thunk),
  72             "Create a new promise object.\n\n"
  73             "@code{make-promise} is a procedural form of @code{delay}.\n"
  74             "These two expressions are equivalent:\n"
  75             "@lisp\n"
  76             "(delay @var{exp})\n"
  77             "(make-promise (lambda () @var{exp}))\n"
  78             "@end lisp\n")
  79 #define FUNC_NAME s_scm_make_promise
  80 {
  81   SCM_VALIDATE_THUNK (1, thunk);
  82   SCM_RETURN_NEWSMOB2 (scm_tc16_promise,
  83                        SCM_UNPACK (thunk),
  84                        scm_make_recursive_mutex ());
  85 }
  86 #undef FUNC_NAME
  87
  88 static int
  89 promise_print (SCM exp, SCM port, scm_print_state *pstate)
  90 {
  91   int writingp = SCM_WRITINGP (pstate);
  92   scm_puts ("#<promise ", port);
  93   SCM_SET_WRITINGP (pstate, 1);
  94   scm_iprin1 (SCM_PROMISE_DATA (exp), port, pstate);
  95   SCM_SET_WRITINGP (pstate, writingp);
  96   scm_putc ('>', port);
  97   return !0;
  98 }
  99
 100 SCM_DEFINE (scm_force, "force", 1, 0, 0,
 101             (SCM promise),
 102             "If the promise @var{x} has not been computed yet, compute and\n"
 103             "return @var{x}, otherwise just return the previously computed\n"
 104             "value.")
 105 #define FUNC_NAME s_scm_force
 106 {
 107   SCM_VALIDATE_SMOB (1, promise, promise);
 108   scm_lock_mutex (SCM_PROMISE_MUTEX (promise));
 109   if (!SCM_PROMISE_COMPUTED_P (promise))
 110     {
 111       SCM ans = scm_call_0 (SCM_PROMISE_DATA (promise));
 112       if (!SCM_PROMISE_COMPUTED_P (promise))
 113         {
 114           SCM_SET_PROMISE_DATA (promise, ans);
 115           SCM_SET_PROMISE_COMPUTED (promise);
 116         }
 117     }
 118   scm_unlock_mutex (SCM_PROMISE_MUTEX (promise));
 119   return SCM_PROMISE_DATA (promise);
 120 }
 121 #undef FUNC_NAME
 122
 123
 124 SCM_DEFINE (scm_promise_p, "promise?", 1, 0, 0,
 125             (SCM obj),
 126             "Return true if @var{obj} is a promise, i.e. a delayed computation\n"
 127             "(@pxref{Delayed evaluation,,,r5rs.info,The Revised^5 Report on Scheme}).")
 128 #define FUNC_NAME s_scm_promise_p
 129 {
 130   return scm_from_bool (SCM_TYP16_PREDICATE (scm_tc16_promise, obj));
 131 }
 132 #undef FUNC_NAME
 133
 134 void
 135 scm_init_promises ()
 136 {
 137   scm_tc16_promise = scm_make_smob_type ("promise", 0);
 138   scm_set_smob_print (scm_tc16_promise, promise_print);
 139
 140 #include "libguile/promises.x"
 141
 142   scm_add_feature ("delay");
 143 }
 144
 145 /*
 146   Local Variables:
 147   c-file-style: "gnu"
 148   End:
 149 */
 150