One of the neat things about Clojure (maybe all functional languages) is
that functions can be defined either extensionally or intensionally. How
can one create a Clojure structure that mixes these two types of
definition?
That is, I would like to define a function f that saves its result the
first time it is called against any particular argument so that if and
when f is later called against the same argument, it does a look-up via
a hash map rather than repeating a possibly expensive computation. I
think I see how to do this with a ref to a mutable map (where, given an
argument k, f would first try to find (f k) in the map but, if k is not
currently a key of the map, the function would compute the value v = (f
k) and then, in addition to returning v, add the entry <k v> to the map
as a side effect. But this seems ugly. Is there some way to do what I
want here without making explicit use of refs?
Lazy-seqs don't give me what I want because the arguments to be given to
f don't occur in any kind of predictable sequence.
--Larry
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