fresh, freshen break referential transparency

[GoogleCodeExporter]

See following transcript:

prompt> let b = [fresh 'a', fresh 'a']

prompt> b

['x1043,'x1044] : [Symbol]
prompt> b

['x1043,'x1044] : [Symbol]
prompt> freshen b                     

(['x1049,'x1050],[('x1043,'x1049),('x1044,'x1050)]) : 
([Symbol],[(Symbol,Symbol)])

Same input results in different values --> referential transparency broken. 
This is not acceptable in a pure language. At least (fresh, freshen) should 
live in the IO monad.

Original issue reported on code.google.com by ggr...@gmail.com on 7 Dec 2010 at 12:10