Random string generator

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open System
let ranStr n = 
    let r = Random()
    let chars = Array.concat([[|'a' .. 'z'|];[|'A' .. 'Z'|];[|'0' .. '9'|]])
    let sz = Array.length chars in
    String(Array.init n (fun _ -> chars.[r.Next sz]))

// > ranStr 100_000_000;;
// Real: 00:00:01.555, CPU: 00:00:01.575, GC gen0: 1, gen1: 1

namespace System

val ranStr : n:int -> String

Full name: Script.ranStr

val n : int

val r : Random

Multiple items
type Random =
  new : unit -> Random + 1 overload
  member Next : unit -> int + 2 overloads
  member NextBytes : buffer:byte[] -> unit
  member NextDouble : unit -> float

Full name: System.Random

--------------------
Random() : unit
Random(Seed: int) : unit

val chars : char []

type Array =
  member Clone : unit -> obj
  member CopyTo : array:Array * index:int -> unit + 1 overload
  member GetEnumerator : unit -> IEnumerator
  member GetLength : dimension:int -> int
  member GetLongLength : dimension:int -> int64
  member GetLowerBound : dimension:int -> int
  member GetUpperBound : dimension:int -> int
  member GetValue : [<ParamArray>] indices:int[] -> obj + 7 overloads
  member Initialize : unit -> unit
  member IsFixedSize : bool
  ...

Full name: System.Array

val concat : arrays:seq<'T []> -> 'T []

Full name: Microsoft.FSharp.Collections.Array.concat

val sz : int

val length : array:'T [] -> int

Full name: Microsoft.FSharp.Collections.Array.length

Multiple items
type String =
  new : value:char -> string + 7 overloads
  member Chars : int -> char
  member Clone : unit -> obj
  member CompareTo : value:obj -> int + 1 overload
  member Contains : value:string -> bool
  member CopyTo : sourceIndex:int * destination:char[] * destinationIndex:int * count:int -> unit
  member EndsWith : value:string -> bool + 2 overloads
  member Equals : obj:obj -> bool + 2 overloads
  member GetEnumerator : unit -> CharEnumerator
  member GetHashCode : unit -> int
  ...

Full name: System.String

--------------------
String(value: nativeptr<char>) : unit
String(value: nativeptr<sbyte>) : unit
String(value: char []) : unit
String(c: char, count: int) : unit
String(value: nativeptr<char>, startIndex: int, length: int) : unit
String(value: nativeptr<sbyte>, startIndex: int, length: int) : unit
String(value: char [], startIndex: int, length: int) : unit
String(value: nativeptr<sbyte>, startIndex: int, length: int, enc: Text.Encoding) : unit

val init : count:int -> initializer:(int -> 'T) -> 'T []

Full name: Microsoft.FSharp.Collections.Array.init

Random.Next() : int
Random.Next(maxValue: int) : int
Random.Next(minValue: int, maxValue: int) : int