/*

   eval.c

   This software is free software; you can redistribute it and/or
   modify it under the terms of the GNU Library General Public
   License as published by the Free Software Foundation; either
   version 2 of the License, or (at your option) any later version.

   This software 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
   Library General Public License for more details.

   You should have received a copy of the GNU Library General Public
   License along with this software; if not, write to the Free
   Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.

   Original copyright notice follows:

   Copyright, 1993, Brent Benson.  All Rights Reserved.
   0.4 & 0.5 Revisions Copyright 1994, Joseph N. Wilson.  All Rights Reserved.

   Permission to use, copy, and modify this software and its
   documentation is hereby granted only under the following terms and
   conditions.  Both the above copyright notice and this permission
   notice must appear in all copies of the software, derivative works
   or modified version, and both notices must appear in supporting
   documentation.  Users of this software agree to the terms and
   conditions set forth in this notice.

 */

#include "eval.h"

#include "alloc.h"
#include "apply.h"
#include "env.h"
#include "error.h"
#include "list.h"
#include "print.h"
#include "syntax.h"

struct eval_stack *eval_stack = 0;

/* local function prototypes */
Object eval_combination (Object obj, int do_apply);

/* function definitions */

Object
eval (Object obj)
{
    Object val;

#ifdef SMALL_OBJECTS
    if (INTEGERP (obj) || IMMEDP (obj)) {
	return (obj);
    }
#endif

#ifdef SMALL_OBJECTS
    switch (POINTERTYPE (obj))
#else
    switch (TYPE (obj))
#endif
    {
    case True:
    case False:
    case Integer:
#ifdef BIG_INTEGERS
    case BigInteger:
#endif
    case Ratio:
    case SingleFloat:
    case DoubleFloat:
    case ByteString:
    case SimpleObjectVector:
    case Keyword:
    case Character:
    case EndOfFile:
    case EmptyList:		/* is this right? */
    case ForeignPtr:		/* <pcb> */
	return (obj);
    case Values:
	if (obj == unspecified_object) {
	    return obj;
	} else {
	    return error ("Trying to eval a values object (this is a bug)",
			  obj,
			  NULL);
	}
    case Symbol:
	val = symbol_value (obj);
	if (!val) {
	    return error ("unbound variable", obj, NULL);
	}
	return (val);
    case Pair:
	return (eval_combination (obj, 0));
    default:
	return error ("eval: do not know how to eval object", obj, NULL);
    }
}

jmp_buf *the_eval_context = NULL;
static Object the_eval_obj = NULL;

extern struct frame *the_env;
extern Object standard_error_stream;
extern Object unwind_protect_symbol;

Object
tail_eval (Object obj)
{

#ifdef OPTIMIZE_TAIL_CALLS
    if (trace_functions) {
	warning ("in tail eval context, parent context",
		 eval_stack->context,
		 eval_stack->next->context,
		 0);
    }
    if (PAIRP (obj)) {
	the_eval_obj = obj;
	if (the_eval_context == NULL) {
	    error ("tail_eval called without a prior eval in progress.", NULL);
	}
	longjmp (*the_eval_context, 1);
    }
#endif
    /* if it's not a <pair>, then call good old eval. */
    return eval (obj);
}

/* <pcb> moved apply here to permit safe tail recursion. */

Object
apply (Object fun, Object args)
{
    return eval_combination (cons (fun, args), 1);
}

Object
eval_combination (Object obj, int do_apply)
{
    Object op;
    syntax_fun sf;
    Object fun, args, ret;
    struct frame *old_env;
    struct eval_stack *old_stack;
    jmp_buf *old_context;
    jmp_buf this_context;
    int is_tail_call = 0;
    Object tail_required_values;
    Object tail_rest_values;

    ResultValueStack = cons (default_result_value (), ResultValueStack);

    old_env = the_env;
    old_stack = eval_stack;

    /* save a place for tail_eval to longjmp to later. */
    old_context = the_eval_context;
    the_eval_context = &this_context;
    if (setjmp (this_context) != 0) {
	obj = the_eval_obj;

	eval_stack = old_stack;	/* restore the state of the "eval" stack. */

	is_tail_call = 1;	/* a tail call occurred. */
	do_apply = 0;		/* tail_eval called from apply. */
    }
    if (do_apply) {
	fun = CAR (obj);
	args = CDR (obj);
	push_eval_stack (fun);
	ret = apply_internal (fun, args);
	pop_eval_stack ();
    } else {
	op = CAR (obj);
	sf = syntax_function (op);
	if (sf) {
	    push_eval_stack (op);
	    ret = (*sf) (obj);
	    pop_eval_stack ();
	} else {
	    fun = eval (CAR (obj));
	    push_eval_stack (fun);
	    args = map (eval, CDR (obj));
	    ret = apply_internal (fun, args);
	    pop_eval_stack ();
	}
    }

    /* restore previous frame's context. */
    the_eval_context = old_context;

    /* here we restore the environment since is not restored via tail calls. */
    if (is_tail_call)
	the_env = old_env;

    tail_required_values = CAR (CAR (ResultValueStack));
    tail_rest_values = CDR (CAR (ResultValueStack));
    ResultValueStack = CDR (ResultValueStack);

    ret = construct_return_values (ret,
				   tail_required_values,
				   tail_rest_values);
    return ret;
}

void
pop_eval_stack (void)
{
    eval_stack = eval_stack->next;
}

void
push_eval_stack (Object obj)
{
    struct eval_stack *tmp =
    (struct eval_stack *) checking_malloc (sizeof (struct eval_stack));

    tmp->next = eval_stack;
    tmp->context = obj;
    tmp->frame = the_env;
    eval_stack = tmp;
}

Object
print_stack (void)
{
    struct eval_stack *entry;
    int i;

    for (i = 0, entry = eval_stack->next;
	 entry != NULL;
	 entry = entry->next, i++) {
	fprintf (stderr, "#%d ", i);
	print_object (standard_error_stream, entry->context, 1);
	fprintf (stderr, "\n");
    }
    return unspecified_object;
}