[Ironruby-core] Problem with ironruby on mono

[ras]

Hi all,
I've successfully compiled (with rake compile mono=1) IronRuby 
under Linux with Mono but whe I try to execute some code I get 
a strange behaviour, for example:

$ mono rbx.exe
0.1
Copyright (c) Microsoft Corporation. All rights reserved.
>>> a = 1
=> 1
>>> puts a
unknown: undefined local variable or method `a' for main:Object (NoMethodError)
>>> b = a + 1
unknown: undefined local variable or method `a' for main:Object (NoMethodError)
>>> a.class
unknown: undefined local variable or method `a' for main:Object (NoMethodError)
>>> 

and so on...
where's the problem?

some info:
$ mono -V
Mono JIT compiler version 1.9 (/trunk/ r95320)
Copyright (C) 2002-2007 Novell, Inc and Contributors. www.mono-project.com
        TLS:           __thread
        GC:            Included Boehm (with typed GC)
        SIGSEGV:       altstack
        Notifications: epoll
        Architecture:  x86
        Disabled:      none

$ mono rbx.exe -V
IronRuby 0.1 on .NET 2.0.0.0



TIA,
   ras