Debugger strangeness

[Jos Backus]

lizzy:~% cat r
class Foo
def initialize(s)
@s = s
end

def bar
@s
end
end

f = Foo.new("string")
p f.bar
lizzy:~% ruby -rdebug r
Debug.rb
Emacs support available.

r:1:class Foo
(rdb:1) help
Debugger help v.-0.002b
Commands
b[reak] [file:|class:]<line|method>
b[reak] [class.]<line|method>
set breakpoint to some position
...
(rdb:1) b Foo.bar
r:1:uninitialized constant Foo
(rdb:1) b Foo:bar
Set breakpoint 1 at Foo:bar
(rdb:1) c
"string"
lizzy:~% # Breakpoint didn't work

How is this supposed to work?