libguile/promises.c

   1 /* Copyright (C) 1995,1996,1997,1998,1999,2000,2001,2002,2003,2004,2005,2006,2007,2008,2009,2010,2011
   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/list.h"
  45 #include "libguile/macros.h"
  46 #include "libguile/memoize.h"
  47 #include "libguile/modules.h"
  48 #include "libguile/ports.h"
  49 #include "libguile/print.h"
  50 #include "libguile/procprop.h"
  51 #include "libguile/programs.h"
  52 #include "libguile/root.h"
  53 #include "libguile/smob.h"
  54 #include "libguile/srcprop.h"
  55 #include "libguile/stackchk.h"
  56 #include "libguile/strings.h"
  57 #include "libguile/threads.h"
  58 #include "libguile/throw.h"
  59 #include "libguile/validate.h"
  60 #include "libguile/values.h"
  61 #include "libguile/promises.h"
  62
  63
  64 \f
  65
  66
  67 scm_t_bits scm_tc16_promise;
  68
  69 SCM_DEFINE (scm_make_promise, "make-promise", 1, 0, 0,
  70             (SCM thunk),
  71             "Create a new promise object.\n\n"
  72             "@code{make-promise} is a procedural form of @code{delay}.\n"
  73             "These two expressions are equivalent:\n"
  74             "@lisp\n"
  75             "(delay @var{exp})\n"
  76             "(make-promise (lambda () @var{exp}))\n"
  77             "@end lisp\n")
  78 #define FUNC_NAME s_scm_make_promise
  79 {
  80   SCM_VALIDATE_THUNK (1, thunk);
  81   SCM_RETURN_NEWSMOB2 (scm_tc16_promise,
  82                        SCM_UNPACK (thunk),
  83                        SCM_UNPACK (scm_make_recursive_mutex ()));
  84 }
  85 #undef FUNC_NAME
  86
  87 static int
  88 promise_print (SCM exp, SCM port, scm_print_state *pstate)
  89 {
  90   int writingp = SCM_WRITINGP (pstate);
  91   scm_puts_unlocked ("#<promise ", port);
  92   SCM_SET_WRITINGP (pstate, 1);
  93   scm_iprin1 (SCM_PROMISE_DATA (exp), port, pstate);
  94   SCM_SET_WRITINGP (pstate, writingp);
  95   scm_putc_unlocked ('>', port);
  96   return !0;
  97 }
  98
  99 SCM_DEFINE (scm_force, "force", 1, 0, 0,
 100             (SCM promise),
 101             "If @var{promise} has not been computed yet, compute and\n"
 102             "return @var{promise}, otherwise just return the previously computed\n"
 103             "value.")
 104 #define FUNC_NAME s_scm_force
 105 {
 106   SCM_VALIDATE_SMOB (1, promise, promise);
 107   scm_lock_mutex (SCM_PROMISE_MUTEX (promise));
 108   if (!SCM_PROMISE_COMPUTED_P (promise))
 109     {
 110       SCM ans = scm_call_0 (SCM_PROMISE_DATA (promise));
 111       if (!SCM_PROMISE_COMPUTED_P (promise))
 112         {
 113           SCM_SET_PROMISE_DATA (promise, ans);
 114           SCM_SET_PROMISE_COMPUTED (promise);
 115         }
 116     }
 117   scm_unlock_mutex (SCM_PROMISE_MUTEX (promise));
 118   return SCM_PROMISE_DATA (promise);
 119 }
 120 #undef FUNC_NAME
 121
 122
 123 SCM_DEFINE (scm_promise_p, "promise?", 1, 0, 0,
 124             (SCM obj),
 125             "Return true if @var{obj} is a promise, i.e. a delayed computation\n"
 126             "(@pxref{Delayed evaluation,,,r5rs.info,The Revised^5 Report on Scheme}).")
 127 #define FUNC_NAME s_scm_promise_p
 128 {
 129   return scm_from_bool (SCM_TYP16_PREDICATE (scm_tc16_promise, obj));
 130 }
 131 #undef FUNC_NAME
 132
 133 void
 134 scm_init_promises ()
 135 {
 136   scm_tc16_promise = scm_make_smob_type ("promise", 0);
 137   scm_set_smob_print (scm_tc16_promise, promise_print);
 138
 139 #include "libguile/promises.x"
 140
 141   scm_add_feature ("delay");
 142 }
 143
 144 /*
 145   Local Variables:
 146   c-file-style: "gnu"
 147   End:
 148 */
 149