In a language such as Haskell where you can identify impure functions by their type signatures, you know which ones you can memoize and which you can't. Perl's not quite as easy.

You might be looking for data flow analysis, which is not as easy as it sounds. (For example, proving terminating conditions in the general case is a hard problem.) You can make certain approximations, though.

In reply to Re^3: Good metrics for Memoization by chromatic
in thread Good metrics for Memoization by Trizor

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