/* 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:
*/