Clojure: Idiomatic Way to Insert a Char in a String

Question

I have a string in Clojure and a character I want to put in between the nth and (n+1)st character. For example: Lets say the string is "aple" and I want to insert another "p" between the "p" and the "l".

  (prn 
     (some-function "aple" "p" 1 2)) 

  ;; prints "apple" 
  ;; ie "aple" -> "ap" "p" "le" and the concatenated back together.

I'm finding this somewhat challenging, so I figure I am missing information about some useful function(s) Can someone please help me write the "some-function" above that takes a string, another string, a start position and an end position and inserts the second string into the first between the start position and the end position? Thanks in advance!

Answer 1

More efficient than using seq functions:

(defn str-insert
  "Insert c in string s at index i."
  [s c i]
  (str (subs s 0 i) c (subs s i)))

From the REPL:

user=> (str-insert "aple" "p" 1)
"apple"

NB. This function doesn't actually care about the type of c, or its length in the case of a string; (str-insert "aple" \p 1) and (str-insert "ale" "pp" 1) work also (in general, (str c) will be used, which is the empty string if c is nil and (.toString c) otherwise).

Since the question asks for an idiomatic way to perform the task at hand, I will also note that I find it preferable (in terms of "semantic fit" in addition to the performance advantage) to use string-oriented functions when dealing with strings specifically; this includes subs and functions from clojure.string. See the design notes at the top of the source of clojure.string for a discussion of idiomatic string handling.