as-transducer: convenience function to make a full transducer from a reducing-step function which accepts three arguments: the transforming function (xf), the reduced value, and the step value from the reduction.

as-transducer.clj

(defn as-transducer [f]
  "Convert function f into a transducer function.

  This is merely a more convenient way to write an efficient reducing-step
  function without the transducer signature.

  The function should have the signature `(f transformer opaque-collection value)`
  and return either `opaque-collection` or the return value of
  `(transformer opaque-collection value)` to return new `opaque-collection`
  things with `value` \"added\" to it. It can also box its return value with
  `reduced` to terminate reduction early."
  (fn [xf]
    (fn
      ([] (xf))
      ([r] (xf r))
      ([r v] (f xf r v)))))