// Catch Code.
//
// File:        catch.cc
// Author:      course
// Version:     2

#include "lisp.h"

// Pointer to top of catch_area stack.  NULL is stack
// empty.  Initialized to NULL.
//
catch_area * catch_area::current;

void catch_area::initialize()
{
    current = NULL;
}


// Save everything in catch_area.  Push this catch_area
// into the catch_area stack, and return the address of
// the jmp_buf in this catch area for use by setjmp.
//
jmp_buf_pointer catch_area::save (object * tag)
{
    catch_save		= catch_area::current;
    preserve_save	= preserve_stack::current;
    environment_save	= environment;
    this->tag		= tag;
    value		= NULL;

    catch_area::current	= this;

    return (this->jmp_save);
}

// Restore everything in this catch_area and return the
// value of the area.
//
object * catch_area::restore ()
{
    catch_area::current	= catch_save;
    preserve_stack::current	= preserve_save;
    environment		= environment_save;

    return (value);
}

// Throw a value to a tag.  A search is made of the
// catch stack for a catch area with the same tag,
// and the first one found is restored.  If none are
// found, error is called.
//
void lisp_throw (object * tag, object * value)
{
    for ( catch_area * area = catch_area::current;
	  area != NULL;
	  area = area->catch_save
	)
    {
	if (tag == area->tag)
	{
	    area->value = value;
	    longjmp (area->jmp_save, 1);
	}
    }

    error ( "Throw cannot find catch with tag: ", tag);
}