F#, Split String and .Net methods

Question

I'm new to F#. I'm using VS2008 shell and F# interactive. I try to split a string using "System.String.Split" but then I get the error: "Split is not a static method"

code example:

let Count text =
    let words = System.String.Split [' '] text
    let nWords = words.Length
    (nWords)

How do I use the String methods like split in F# ?

Solution 1

You call them as instance methods:

let Count (text : string) =
  let words = text.Split [|' '|]
  let nWords = words.Length
  (nWords)

(Note you need to use [| |] because Split takes an array not a list; or, as per Joel Mueller's comment, because Split takes a params array, you can just pass in the delimiters as separate arguments (e.g. text.Split(' ', '\n')).)

Solution 2

The function String.split is now defined in the F# Power Pack. You must add

#r "FSharp.PowerPack.dll";; 
#r "FSharp.PowerPack.Compatibility.dll";; 

See the errata for Expert F#: http://www.expert-fsharp.com/Updates/Expert-FSharp-Errata-Jan-27-2009.pdf

Get FSharp.PowerPack.dll here: http://fsharppowerpack.codeplex.com/

Comments

[Joel Mueller]

Split takes a params array, which means you can pass in an array, or you can simply pass in one or more character literals, without an array. text.Split ' ' or text.Split ' ', '\n' (with or without parens) are perfectly valid.

[kvb]

@Joel - Your second example doesn't work; it creates a tuple with '\n' as the second half. It does work when called as text.Split(' ', '\n'), though.

[Joel Mueller]

@kvb - You're right, I misread the output in FSI. I was surprised when it seemed to work.