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/* Copyright (C) 1995,1996,1998,1999,2000,2001 Free Software Foundation, Inc.
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
*
* This library 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
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this library; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*/
#include "libguile/_scm.h"
#include "libguile/eval.h"
#include "libguile/alist.h"
#include "libguile/fluids.h"
#include "libguile/ports.h"
#include "libguile/smob.h"
#include "libguile/dynwind.h"
/* {Dynamic wind}
Things that can be on the wind list:
(enter-proc . leave-proc) dynamic-wind
(tag . jmpbuf) catch
(tag . lazy-catch) lazy-catch
tag is either a symbol or a boolean
((fluid ...) . (value ...)) with-fluids
*/
SCM_DEFINE (scm_dynamic_wind, "dynamic-wind", 3, 0, 0,
(SCM in_guard, SCM thunk, SCM out_guard),
"All three arguments must be 0-argument procedures.\n"
"@var{in_guard} is called, then @var{thunk}, then\n"
"@var{out_guard}.\n"
"\n"
"If, any time during the execution of @var{thunk}, the\n"
"continuation of the @code{dynamic_wind} expression is escaped\n"
"non-locally, @var{out_guard} is called. If the continuation of\n"
"the dynamic-wind is re-entered, @var{in_guard} is called. Thus\n"
"@var{in_guard} and @var{out_guard} may be called any number of\n"
"times.\n"
"@lisp\n"
"(define x 'normal-binding)\n"
"@result{} x\n"
"(define a-cont (call-with-current-continuation\n"
" (lambda (escape)\n"
" (let ((old-x x))\n"
" (dynamic-wind\n"
" ;; in-guard:\n"
" ;;\n"
" (lambda () (set! x 'special-binding))\n"
"\n"
" ;; thunk\n"
" ;;\n"
" (lambda () (display x) (newline)\n"
" (call-with-current-continuation escape)\n"
" (display x) (newline)\n"
" x)\n"
"\n"
" ;; out-guard:\n"
" ;;\n"
" (lambda () (set! x old-x)))))))\n"
"\n"
";; Prints:\n"
"special-binding\n"
";; Evaluates to:\n"
"@result{} a-cont\n"
"x\n"
"@result{} normal-binding\n"
"(a-cont #f)\n"
";; Prints:\n"
"special-binding\n"
";; Evaluates to:\n"
"@result{} a-cont ;; the value of the (define a-cont...)\n"
"x\n"
"@result{} normal-binding\n"
"a-cont\n"
"@result{} special-binding\n"
"@end lisp")
#define FUNC_NAME s_scm_dynamic_wind
{
SCM ans;
SCM_ASSERT (SCM_NFALSEP (scm_thunk_p (out_guard)),
out_guard,
SCM_ARG3, FUNC_NAME);
scm_call_0 (in_guard);
scm_dynwinds = scm_acons (in_guard, out_guard, scm_dynwinds);
ans = scm_call_0 (thunk);
scm_dynwinds = SCM_CDR (scm_dynwinds);
scm_call_0 (out_guard);
return ans;
}
#undef FUNC_NAME
/* The implementation of a C-callable dynamic-wind,
* scm_internal_dynamic_wind, requires packaging of C pointers in a
* smob. Objects of this type are pushed onto the dynwind chain.
*/
#define SCM_GUARDSP(obj) SCM_TYP16_PREDICATE (tc16_guards, obj)
#define SCM_BEFORE_GUARD(obj) ((scm_t_guard) SCM_CELL_WORD (obj, 1))
#define SCM_AFTER_GUARD(obj) ((scm_t_guard) SCM_CELL_WORD (obj, 2))
#define SCM_GUARD_DATA(obj) ((void *) SCM_CELL_WORD (obj, 3))
static scm_t_bits tc16_guards;
static int
guards_print (SCM exp, SCM port, scm_print_state *pstate SCM_UNUSED)
{
scm_puts ("#<guards ", port);
scm_intprint (SCM_UNPACK (SCM_CDR (exp)), 16, port);
scm_putc ('>', port);
return 1;
}
SCM
scm_internal_dynamic_wind (scm_t_guard before,
scm_t_inner inner,
scm_t_guard after,
void *inner_data,
void *guard_data)
{
SCM guards, ans;
before (guard_data);
SCM_NEWSMOB3 (guards, tc16_guards, (scm_t_bits) before,
(scm_t_bits) after, (scm_t_bits) guard_data);
scm_dynwinds = scm_acons (guards, SCM_BOOL_F, scm_dynwinds);
ans = inner (inner_data);
scm_dynwinds = SCM_CDR (scm_dynwinds);
after (guard_data);
return ans;
}
#ifdef GUILE_DEBUG
SCM_DEFINE (scm_wind_chain, "wind-chain", 0, 0, 0,
(),
"Return the current wind chain. The wind chain contains all\n"
"information required by @code{dynamic-wind} to call its\n"
"argument thunks when entering/exiting its scope.")
#define FUNC_NAME s_scm_wind_chain
{
return scm_dynwinds;
}
#undef FUNC_NAME
#endif
void
scm_swap_bindings (SCM vars, SCM vals)
{
SCM tmp;
while (SCM_NIMP (vals))
{
tmp = SCM_VARIABLE_REF (SCM_CAR (vars));
SCM_VARIABLE_SET (SCM_CAR (vars), SCM_CAR (vals));
SCM_SETCAR (vals, tmp);
vars = SCM_CDR (vars);
vals = SCM_CDR (vals);
}
}
void
scm_dowinds (SCM to, long delta)
{
tail:
if (SCM_EQ_P (to, scm_dynwinds));
else if (delta < 0)
{
SCM wind_elt;
SCM wind_key;
scm_dowinds (SCM_CDR (to), 1 + delta);
wind_elt = SCM_CAR (to);
#if 0
if (SCM_INUMP (wind_elt))
{
scm_cross_dynwind_binding_scope (wind_elt, 0);
}
else
#endif
{
wind_key = SCM_CAR (wind_elt);
/* key = #t | symbol | thunk | list of variables | list of fluids */
if (SCM_NIMP (wind_key))
{
if (SCM_CONSP (wind_key))
{
if (SCM_VARIABLEP (SCM_CAR (wind_key)))
scm_swap_bindings (wind_key, SCM_CDR (wind_elt));
else if (SCM_FLUIDP (SCM_CAR (wind_key)))
scm_swap_fluids (wind_key, SCM_CDR (wind_elt));
}
else if (SCM_GUARDSP (wind_key))
SCM_BEFORE_GUARD (wind_key) (SCM_GUARD_DATA (wind_key));
else if (SCM_TYP3 (wind_key) == scm_tc3_closure)
scm_call_0 (wind_key);
}
}
scm_dynwinds = to;
}
else
{
SCM from;
SCM wind_elt;
SCM wind_key;
from = SCM_CDR (SCM_CAR (scm_dynwinds));
wind_elt = SCM_CAR (scm_dynwinds);
scm_dynwinds = SCM_CDR (scm_dynwinds);
#if 0
if (SCM_INUMP (wind_elt))
{
scm_cross_dynwind_binding_scope (wind_elt, 0);
}
else
#endif
{
wind_key = SCM_CAR (wind_elt);
if (SCM_NIMP (wind_key))
{
if (SCM_CONSP (wind_key))
{
if (SCM_VARIABLEP (SCM_CAR (wind_key)))
scm_swap_bindings (wind_key, SCM_CDR (wind_elt));
else if (SCM_FLUIDP (SCM_CAR (wind_key)))
scm_swap_fluids_reverse (wind_key, SCM_CDR (wind_elt));
}
else if (SCM_GUARDSP (wind_key))
SCM_AFTER_GUARD (wind_key) (SCM_GUARD_DATA (wind_key));
else if (SCM_TYP3 (wind_key) == scm_tc3_closure)
scm_call_0 (from);
}
}
delta--;
goto tail; /* scm_dowinds(to, delta-1); */
}
}
void
scm_init_dynwind ()
{
tc16_guards = scm_make_smob_type ("guards", 0);
scm_set_smob_print (tc16_guards, guards_print);
#include "libguile/dynwind.x"
}
/*
Local Variables:
c-file-style: "gnu"
End:
*/
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