Using F# to parse command line options with Mono.Options

README

Sample code on how to parse command line options with Mono.Options.

Mono.Options can be downloaded and compiled from:
https://github.com/mono/mono/tree/master/mcs/class/Mono.Options/Mono.Options

command_line.fs

#light

open System
open Mono.Options

type Options() =
    let mutable m_help    = false
    let mutable m_volume  = null
    let mutable m_fix     = false
    let mutable m_logSize = 0
    
    member this.Help with get()       = m_help
                     and  set newHelp = m_fix <- newHelp
    
    member this.Volume with get()         = m_volume
                       and  set newVolume = m_volume <- newVolume
    
    member this.Fix with get()      = m_fix
                    and  set newFix = m_fix <- newFix
    
    member this.LogSize with get()          = m_logSize
                        and  set newLogSize = m_logSize <- newLogSize

[<EntryPoint>]
let main (args: string[]) =
    Console.WriteLine("Checks a disk and displays a status report.\n")

    let options = new Options()

    let optionSet = new OptionSet()
    optionSet.Add("help",  "Show help message for usage",
        fun v -> options.Help <- true) |> ignore
    optionSet.Add("volume=", "REQUIRED Specifies the drive letter.",
        fun v -> options.Volume <- v) |> ignore
    optionSet.Add("f|F",  "Fixes error on the disk",
        fun v -> options.Fix <- true) |> ignore
    optionSet.Add("l=", "Changes the log file size to the specified number of kilobytes",
        fun v -> options.LogSize <- int v) |> ignore
    optionSet.Parse(args) |> ignore
    
    if options.Help || options.Volume = null then
        Console.WriteLine("Usage message:\n")
        optionSet.WriteOptionDescriptions(Console.Error)
        
        Environment.Exit(-1)
    else
        Console.WriteLine("Received options:\n")
        Console.WriteLine("- volume = {0}", options.Volume)
        Console.WriteLine("- fix = {0}", options.Fix)
        Console.WriteLine("- logSize = {0}", options.LogSize)
    
    0

second_command_line.fs

#light

open System
open Mono.Options

type Arguments() =
    let optionSet = new OptionSet()

    let mutable m_help    = false
    let mutable m_volume  = null
    let mutable m_fix     = false
    let mutable m_logSize = 0

    member this.Help with get()       = m_help
                     and  set newHelp = m_fix <- newHelp

    member this.Volume with get()         = m_volume
                       and  set newVolume = m_volume <- newVolume

    member this.Fix with get()      = m_fix
                    and  set newFix = m_fix <- newFix

    member this.LogSize with get()          = m_logSize
                        and  set newLogSize = m_logSize <- newLogSize

    static member New =
        new Arguments()

    member this.With (option, description, action) =
        optionSet.Add(option, description, fun value -> action this value) |> ignore
        this

    member this.From (args) =
        optionSet.Parse(args) |> ignore
        this

    member this.WriteOptionDescriptions(output) =
        optionSet.WriteOptionDescriptions(output)

[<EntryPointAttribute>]
let main (args) =
    Console.WriteLine("Checks a disk and displays a status report.\n")

    let arguments = Arguments.New
                        .With("help", "Show help message for usage",
                            fun this value -> this.Help <- true)
                        .With("volume=", "REQUIRED Specifies the drive letter.",
                            fun this value -> this.Volume <- value)
                        .With("f|F",  "Fixes error on the disk",
                            fun this value -> this.Fix <- true)
                        .With("l=", "Changes the log file size to the specified number of kilobytes",
                            fun this value -> this.LogSize <- int value)
                        .From(args)

    if arguments.Help || arguments.Volume = null then
        Console.WriteLine("Usage message:\n")
        arguments.WriteOptionDescriptions(Console.Error)

        Environment.Exit(-1)
    else
        Console.WriteLine("Received options:\n")
        Console.WriteLine("- volume = {0}", arguments.Volume)
        Console.WriteLine("- fix = {0}", arguments.Fix)
        Console.WriteLine("- logSize = {0}", arguments.LogSize)

    0

Thanks for this. I was tearing my hair out trying to figure out the syntax for F#.

I simplified it a bit further I think, by using local mutable variables. No need for defining a type to hold the variables. Short syntax example:

let help = ref false
let optionSet = new OptionSet()
optionSet.Add("h|help", "Show help message for usage", fun v -> help := true) |> ignore
optionSet.Parse(argv)
if !help then 
    optionSet.WriteOptionDescriptions (System.Console.Out)
else ...