Parallel Map pmap

Applies a function to each element of a list in parallel using the thread pool and returns a new list with the results.

Syntax

(pmap function list)

Examples

Basic parallel mapping

↪ (pmap (fn [x] (+ x 1)) [1 2 3])
[2 3 4]

↪ (pmap (fn [x] (* x 2)) [1 2 3])
[2 4 6]

Performance comparison with map

;; Heavy sequential work benefits from parallelization
↪ (set work (fn [x] (fold + 0 (til 10000))))

↪ (timeit (map work (til 1000)))
105.99

↪ (timeit (pmap work (til 1000)))
7.05

Notes

• The function is applied to each element in parallel using multiple threads
• Works with any type of list or vector
• Returns a new list without modifying the original
• Best for CPU-intensive tasks where parallel overhead is justified
• For small/fast tasks, sequential map may be faster due to lower overhead
• Thread pool size is determined by system CPU count