charJe/cache-while

THIS PROJECT HAS MOVED

Cache-While

Cache any part of your program based on the values of expressions.

Macro: (cache-while place eqs-values &body body)

place is any setf-able place. That is where the cache will live.

eqs-values is a list of pairs where the first element is an equivalence function (not evaluated) and the second element is an expression (evaluated).

For each place use in a particular call to cache-while, only the most recent result is cache. The cached result is the evaluation of body.

body is re-evaluated if any of the evaluated values in eqs-values is different than the most recent.

Caching based on time

cache-while invalidates the cache when any of the values change. If one of those values is based on time, then you have a timed invalidation.

Invalidate cache every 5 minutes or if value changes. cache is where the cache is to be stored

(cache-while cache
    ((eq value)
     (= (floor (/ (nth-value 1 (get-decoded-time))
                  5))))
  ;; some expensive calculation
  )

Storing cache in session

For web programming you might want each user to have a unique cache.

(cache-while (session-value :cache)
    ((string= (get-parameter "search")))
  ;; something you want to do only when the search GET argument changes
  ;; probably query the database or something
  )