CODEWITHSUNDEEP
clojurelazy-sequences
user4813927
user4813927

Reputation:

Making a function lazy in clojure

I have this function which seems to work fine on limited collections, but not on infinite ones. Is there a way to construct a lazy-seq in it to get it run with infinite coll's, like: (take 3 (m inc (range))) => (1 2 3)?

(defn m [f c] (reduce #(conj % (f %2)) [] c))

Upvotes: 0

Views: 261

Answers (2)

Nils Blum-Oeste
Nils Blum-Oeste

Reputation: 5598

reduce will keep taking elements from a sequence until nil gets returned. As such, reduce will never return on infinite sequences.

As pointed out in the comments, reduced can be used to force the termination of reduce, thanks!

Upvotes: 1

user5187212
user5187212

Reputation: 426

This seems to be a use case for map

(map f c)

or (when it had to be a vector)

(mapv f c)

EDIT: A possible re-implementation of map:

(defn new-map [f coll]
  (if (seq coll)
    (lazy-seq
      (cons (f (first coll)) 
            (new-map f (rest coll))))))

Upvotes: 2

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