catch

/*
 *  call-seq:
 *     catch(symbol) {| | block }  > obj
 *  
 *  +catch+ executes its block. If a +throw+ is
 *  executed, Ruby searches up its stack for a +catch+ block
 *  with a tag corresponding to the +throw+'s
 *  _symbol_. If found, that block is terminated, and
 *  +catch+ returns the value given to +throw+. If
 *  +throw+ is not called, the block terminates normally, and
 *  the value of +catch+ is the value of the last expression
 *  evaluated. +catch+ expressions may be nested, and the
 *  +throw+ call need not be in lexical scope.
 *     
 *     def routine(n)
 *       puts n
 *       throw :done if n <= 0
 *       routine(n-1)
 *     end
 *     
 *     
 *     catch(:done) { routine(3) }
 *     
 *  <em>produces:</em>
 *     
 *     3
 *     2
 *     1
 *     0
 */

static VALUE
rb_f_catch(dmy, tag)
    VALUE dmy, tag;
{
    int state;
    VALUE val = Qnil;           /* OK */

    tag = ID2SYM(rb_to_id(tag));
    PUSH_TAG(tag);
    if ((state = EXEC_TAG()) == 0) {
        val = rb_yield_0(tag, 0, 0, 0, Qfalse);
    }
    else if (state == TAG_THROW && tag == prot_tag->dst) {
        val = prot_tag->retval;
        state = 0;
    }
    POP_TAG();
    if (state) JUMP_TAG(state);

    return val;
}