[plt-scheme] hash-ref 'manipulating' mutable hash-tables?

Hi,

"Caveats concerning concurrent modification: A mutable hash table can
be manipulated with hash-ref,"
--  http://docs.plt-scheme.org/reference/hashtables.html

Is this right? How does hash-ref change a hash table?  (do mutable
ht's do some sort of 'query optimisation' that I'm not aware of? if
so; does this make them faster but less safe than immutable ht's?)


Cheers,

Stephen

--
Stephen De Gabrielle
s.degabrielle at cs.ucl.ac.uk
Telephone +44 (0)20 7679 0693 (x30693)
Mobile 079 851 890 45
Project: Making Sense of Information (MaSI)
Work:http://www.uclic.ucl.ac.uk/annb/MaSI.html
Home:http://www.degabrielle.name/stephen


UCL Interaction Centre
MPEB 8th floor
University College London
Gower Street
London WC1E 6BT