How To Change List of Chars To String?

Question

In F# I want to transform a list of chars into a string. Consider the following code:

let lChars = ['a';'b';'c'] 

If I simply do lChars.ToString, I get "['a';'b';'c']". I'm trying to get "abc". I realize I could probably do a List.reduce to get the effect I'm looking for but it seems like there should be some primitive built into the library to do this.

To give a little context to this, I'm doing some manipulation on individual characters in a string and when I'm done, I want to display the resulting string.

I've tried googling this and no joy that way. Do I need to just bite the bullet and build a List.reduce expression to do this transformation or is there some more elegant way to do this?

Answer 1

Have you tried

System.String.Concat(Array.ofList(lChars)) 

Answer 2

How many ways can you build a string in F#? Here's another handful:

let chars = ['H';'e';'l';'l';'o';',';' ';'w';'o';'r';'l';'d';'!']  //Using an array builder let hw1 = new string [|for c in chars -> c|]  //StringBuilder-Lisp-like approach open System.Text let hw2 =      string (List.fold (fun (sb:StringBuilder) (c:char) -> sb.Append(c))                        (new StringBuilder())                        chars)  //Continuation passing style let hw3 =     let rec aux L k =         match L with         | [] -> k ""         | h::t -> aux t (fun rest -> k (string h + rest) )     aux chars id 

Edit: timings may be interesting? I turned hw1..3 into functions and fed them a list of 500000 random characters:

• hw1: 51ms
• hw2: 16ms
• hw3: er... long enough to grow a beard? I think it just ate all of my memory.