Question

Does anyone know if there is a builtin function for reading from the console likewise to the printfn function?
The only method I’ve seen so far is using System.Console.Read() but it doesn’t feel as functional as using a construct like printfn is.

Answer 1

It is indeed a shame that there is no such built-in function. However, as Brian mentioned in a comment on Benjol’s answer, it is possible to build a scanf function yourself. Here’s a quick sketch of how one might define a sscanf variant, although only %s placeholders are implemented:

open System
open System.Text
open System.Text.RegularExpressions
open Microsoft.FSharp.Reflection

let sscanf (pf:PrintfFormat<_,_,_,_,'t>) s : 't =
  let formatStr = pf.Value
  let constants = formatStr.Split([|"%s"|], StringSplitOptions.None)
  let regex = Regex("^" + String.Join("(.*?)", constants |> Array.map Regex.Escape) + "$")
  let matches = 
    regex.Match(s).Groups 
    |> Seq.cast<Group> 
    |> Seq.skip 1
    |> Seq.map (fun g -> g.Value |> box)
  FSharpValue.MakeTuple(matches |> Seq.toArray, typeof<'t>) :?> 't


let (a,b) = sscanf "(%s, %s)" "(A, B)"
let (x,y,z) = sscanf "%s-%s-%s" "test-this-string"