Don't know how to create ISeq from: Java.lang.Long

Question

Doing some practice on recursion and map implementation to knock some rust off Clojure. I'm using lists only here so how am I trying to mix seq and non-seqable stuff?

(defn mapset
  ([operator operand] (mapset operator operand '()))
  ([operator operand finished-set]
   (if (empty? operand)
     '(finished-set)
     (mapset operator (rest operand) (into finished-set (operator (first operand)))))))

REPL:

namespace.name> (mapset + '(1 3 4 6 5))
Execution error (IllegalArgumentException) at tester.core/mapset (core.clj:38).
Don't know how to create ISeq from: java.lang.Long

Answer 1

Some errors:

• replace '(finished-set) with finished-set
• into adds elements from one collection to another, I think you're looking for conj (that's the source of IllegalArgumentException)
• and if you'll use conj, you have to use [] as initial finished-set, because conj adds element to beginning of the list, but at the end of the vector

Your function, with minimal changes:

(defn mapset
  ([operator operand] (mapset operator operand []))
  ([operator operand finished-set]
   (if (empty? operand)
     finished-set
     (mapset operator (rest operand) (conj finished-set (operator (first operand)))))))

Tests:

(mapset inc '(1 3 4 6 5))
; => [2 4 5 7 6]

(mapset dec '(1 3 4 6 5))
; => [0 2 3 5 4]

You can also write it with only two arguments, using cons:

(defn mapset [operator operand]
  (if (empty? operand) 
    '()
    (cons (operator (first operand))
          (mapset operator (rest operand)))))

Note that neither version is lazy, that would require adding lazy-seq.