> I can easily understand how + can be built but am having trouble with
> building ? (zero or one).
If there is a regular expression e for the empty word, one can define ? as
a? = e | a
If there is a regular expression o that never matches one can define e as
e = o*
If there are character classes one can define o as
o = []
Apart from that, I have no idea..
Sebastian
_______________________________________________
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe
