yield

static VALUE
proc_call(int argc, VALUE *argv, VALUE procval)
{
    rb_proc_t *proc;
    rb_block_t *blockptr = 0;
    rb_iseq_t *iseq;
    GetProcPtr(procval, proc);

    iseq = proc->block.iseq;
    if (BUILTIN_TYPE(iseq) == T_NODE || iseq->arg_block != -1) {
        if (rb_block_given_p()) {
            rb_proc_t *proc;
            VALUE procval;
            procval = rb_block_proc();
            GetProcPtr(procval, proc);
            blockptr = &proc->block;
        }
    }

    return rb_vm_invoke_proc(GET_THREAD(), proc, proc->block.self,
                             argc, argv, blockptr);
}