Ancestors

Toot

Written by Olical on 2025-01-21 at 14:00

Fennel functions created with the lambda keyword throw a runtime error if given a nil argument unless the name is prefixed by ? - super useful!

(lambda [x ?y z]
  (print (- x (* (or ?y 1) z))))

In this case, x and z are required, y can be nil.

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Descendants

Written by Olical on 2025-01-21 at 14:02

The tail! marker gives you compile time checking that you haven't broken a tail call!

(fn process-all [data i]
  (case (process (. data i))
    :done (print "Process completed.")
    :next (process-all data (+ i 1))
    :skip (do (tail! (process-all data (+ i 2)))
;;             ^^^^^ Compile error: Must be in tail position
              (print "Skipped" (+ i 1)))))

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