Should be easy to implement one. Something like this:
class (Monad m) => MonadIntern e m | e -> m where
intern :: e -> m e
instance (Ord e) => MonadIntern e (State (M.Map e e)) where
intern = modify . insertWith (\old new -> old))
2009/9/5 Günther Schmidt
Hi all,
I'm reading in a data of 216k records into a map of Key, Values Pairs, the values being strings.
As it happens out of 216k String values there really are only about 6.6k distinct string values, so I could save a lot of RAM if I was able to "insert" only actually *new* string values into the map and use references to (string) values that already are in memory instead.
Is there a container that would, if I wanted to insert an element, return a pair of either the previously inserted, equal value and the container unchanged, or the new, previously unknown value and the new container amended by that element?
Günther
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