def find_symbol(sym, ctx)
      ctx.each do |h|
        if val = resolve_in(h, sym)
          return val
        end
      end

      nil
    end
def find_symbol(sym, ctx)
      ctx.each do |h|
        if val = resolve_in(h, sym)
          return val
        end
      end

      nil
    end
search for a symbol introduced in the lexical context