Something I found interesting when playing with the example code is that, while folding in parallel certainly speeds up the execution for realized sequences, it

Something I found interesting when playing with the example code is that, while folding in parallel certainly speeds up the execution for realized sequences, it may not make sense to realize a sequence that you're only going to use for one operation: user=> (require '[clojure.core.reducers :as r]) user=> (def s (range 9999999)) user=> (time (r/fold + (r/map inc (r/filter even? s)))) "Elapsed time: 450.318641 msecs" 25000000000000 user=> (time (r/fold + (r/map inc (r/filter even? (vec s))))) "Elapsed time: 463.632907 msecs" 25000000000000 Note the `(vec s)` instead of just `s` in the second timed run above user=> (def sv (vec s)) user=> (time (r/fold + (r/map inc (r/filter even? sv)))) "Elapsed time: 156.731683 msecs" 25000000000000 Far from a ~3x speedup (in these contrived examples), realizing the sequence in-line yields approximately the same performance as if it was operated on lazily. Something to keep in mind if you're trying to optimize your Clojure. This is still the best resource I've read on reducers/transducers :) [edit: code formatting]