[E-Lang] Immutable map operations

[hal@finney.org]

MarkM writes:
> One day a maintenance programmer changes Alice so that the 'list' passed to 
> BlobMaker is mutable.  If an unmutated mutable list responds to the set of 
> messages actually being used just as an immutable list would, everything, 
> including Mallet, continues to work perfectly the next day, and so the bug 
> isn't easily caught.  However, Mallet's been accidentally given the 
> opportunity to corrupt the blob.

Isn't it risky to rely for security on the fact that an object will only
respond to messages with particular names?  It seems like this kind of
problem could arise in other contexts.  I remember one of my concerns
with the MintMaker code was that Assays and Purses responded to some of
the same messages and in some contexts you could substitute one for the
other, causing surprising results.  Is this a serious problem, or can
it be easily avoided?

Hal