// Symbol Code.
//
// File:        symbol.cc
// Author:      {your name} <{your e-mail address}>
// Assignment:  7, 9

#include "symbol.h"
#include "obtype.h"
#include "preserve.h"
#include "gc.h"

class symbol_type : public object_type
{

public:

    symbol_type () : object_type ("SYMBOL") {}
	// Construct object type with simple free and
	// used lists and the name "SYMBOL".

    virtual void initialize();
	// Initialize T, :TEST, TOP_LEVEL, etc.
    virtual void mark();
	// Mark symbols.
    friend symbol * make_symbol (char * name);
};

object_type * SYMBOL_TYPE =
    (object_type *) new symbol_type;

// Create a symbol with a give name.
//
symbol * make_symbol (char * name)
{
    // ***** Write symbol allocator here for *****
    // ***** assignment 7, and modify for    *****
    // ***** assignment 9 gc                *****

    static symbol dummy;

    dummy.init_object (SYMBOL_TYPE);
    return &dummy;
}

object * NIL;
object * T;
object * TEST;
object * TOP_LEVEL;
object * TRACE;
object * STEP;

// Initialize NIL, T, ....
//
void symbol_type::initialize()
{
    T = make_symbol ("T");
    set_symbol_value (unchecked_must_be_symbol(T), T);

    TEST = make_symbol (":TEST");
    set_symbol_value
	(unchecked_must_be_symbol(TEST), TEST);

    TRACE = make_symbol ("*TRACE*");
    set_symbol_value
	(unchecked_must_be_symbol(TRACE), NIL);

    STEP = make_symbol ("*STEP*");
    set_symbol_value
	(unchecked_must_be_symbol(STEP), NIL);

    TOP_LEVEL = make_symbol ("TOP-LEVEL");
}

// Print symbol.
//
ostream& symbol::print (ostream& s)
{
    return s << name;
}

// Scavenge symbol.
//
void symbol::scavenge()
{
    // ***** Put gc code here for assignment 9 ***** 
}

// Mark symbols.
//
void symbol_type::mark()
{
    // ***** Put gc code here for assignment 9 ***** 
}

// A function to help LISP interpreter initialization by
// preserving all symbols defined during program
// initialization before main is called.  Preserve is
// called for all existing symbols.
//
void preserve_all_existing_symbols()
{
    for ( object * ob = SYMBOL_TYPE->used_list;
	  ob != NULL;
	  ob = ob->link
	)
	preserve (ob);
}