An exception has occurred:
    No method 'call' on an instance of Fixnum. (NoMethodError)

Backtrace:
        Kernel(Fixnum)#method_missing at kernel/delta/kernel.rb:13
                    Object#with_block at bp.rb:2
                      main.__script__ at bp.rb:5
    CompiledMethod#activate_as_script at kernel/common/compiled_method.rb:230
             CompiledMethod#as_script at kernel/common/compiled_method.rb:223
                  Compile.single_load at kernel/common/compile.rb:264
          Compile.load_from_extension at kernel/common/compile.rb:309
                    Object#__script__ at kernel/loader.rb:257

> cat bp.rb
def with_block(&prc)
  prc.call(1) # If you inspect prc here, it is a Proc, but..
end

with_block do |z|
  STDERR.puts z
end