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Lippert's Comma Challenge Revisited

Stumbled upon this challenge and tried my hand: http://themechanicalbride.blogspot.com/2009/04/f-solution-to-eric-lippert-challenge.html The original challenge calls for a string result, so there's no issue with converting the sequence to a list from the outset since we need to enumerate it completely anyway; had it insisted on returning a sequence my answer would be different. > commaize ["ABC"; "DEF"; "G"; "H"];; val it : string = "ABC, DEF, G and H"

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    let commaize s =
        let rec insert_commas list = 
            match List.length list with
            | 0 -> []
            | 1 -> list
            | 2 -> list.Head :: " and " :: list.Tail
            | _ -> list.Head :: ", " :: insert_commas list.Tail

        String.concat "" (Seq.toList s |> insert_commas )

val commaize : s:seq<string> -> string

Full name: Script.commaize

val s : seq<string>

val insert_commas : (string list -> string list)

Multiple items
val list : string list

--------------------
type 'T list = List<'T>

Full name: Microsoft.FSharp.Collections.list<_>

Multiple items
module List

from Microsoft.FSharp.Collections

--------------------
type List<'T> =
  | ( [] )
  | ( :: ) of Head: 'T * Tail: 'T list
  interface IEnumerable
  interface IEnumerable<'T>
  member Head : 'T
  member IsEmpty : bool
  member Item : index:int -> 'T with get
  member Length : int
  member Tail : 'T list
  static member Cons : head:'T * tail:'T list -> 'T list
  static member Empty : 'T list

Full name: Microsoft.FSharp.Collections.List<_>

val length : list:'T list -> int

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

property List.Head: string

property List.Tail: string list

module String

from Microsoft.FSharp.Core

val concat : sep:string -> strings:seq<string> -> string

Full name: Microsoft.FSharp.Core.String.concat

module Seq

from Microsoft.FSharp.Collections

val toList : source:seq<'T> -> 'T list

Full name: Microsoft.FSharp.Collections.Seq.toList

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More information

Link:	http://fssnip.net/t6
Posted:	9 years ago
Author:	Hugh Gleaves
Tags:	challenge , lippert , comma , string , concatenate