Write a recursive ml function that uses pattern matching

Question

Problem

Write a recursive ML function that uses pattern matching with name/type

optconcat : char option list -> string

that inputs a list of char options, and returns a single string consisting of all characters on the list concatenated together while ignoring any instances of NONE. For example,

- optconcat([SOME #"b",NONE,SOME #"o",SOME #"o",NONE]);

val it = "boo" : string

- optconcat([NONE,NONE]);

val it = "" : string

The response should include a reference list. Double-space, using Times New Roman 12 pnt font, one-inch margins, and APA style of writing and citations.