Docopt.fs is a F# port of docopt

let ``Docopt.fs`` = docopt |> ``F#`` in

---

Isn't it awesome how CommandLineParser and PowerArgs generate help messages based on your code?!

Hell no! You know what's awesome? It's when the option parser is generated based on the beautiful help message that you write yourself! This way you don't need to write this stupid repeatable parser-code, and instead can write only the help message—the way you want it.

Docopt.fs helps you create most beautiful command-line interfaces easily:

open Docopt

let doc = """
Naval Fate.

Usage:
  naval_fate.exe ship new <name>...
  naval_fate.exe ship <name> move <x> <y> [--speed=<kn>]
  naval_fate.exe ship shoot <x> <y>
  naval_fate.exe mine (set|remove) <x> <y> [--moored | --drifting]
  naval_fate.exe (-h | --help)
  naval_fate.exe --version

Options:
  -h --help     Show this screen.
  --version     Show version.
  --speed=<kn>  Speed in knots [default: 10].
  --moored      Moored (anchored) mine.
  --drifting    Drifting mine.
"""

[<EntryPoint>]
let main argv =
  let docopt = new Docopt(doc)
  try
    let dict = docopt.Parse(argv)
    printfn "Success:\n%A" dict
    0
  with ArgvException(message) ->
    printfn "Error: %s" message
    -42

Beat that! The option parser is generated based on the docstring above that is passed to the Docopt.Parse method. Docopt.Parse parses the usage pattern (doc in this example) and option descriptions (lines starting with dash -) and ensures that the program invocation matches the usage pattern. It parses options, arguments and commands based on that. The basic idea is that a good help message has all necessary information in it to make a parser.

Differences from reference python implementation

• This port should be fully Docopt language compatible with the python reference implementation.
• Currently, if --help or --version is matched, nothing is done by the library and the user must write the help message or the version himself.
• The returned dictionary maps strings to Docopt.Arguments.Result, a discriminated union wrapping the results.
• If a key is not registered in the dictionary, its value is always Result.None instead of throwing a KeyNotFoundException to allow better pattern matching.
• The parsing is done thanks to the parser combinator library FParsec instead of regular expressions.

Compiling

TODO

Installation

TODO

Testing

After compiling, you can run the TestCases.exe binary in bin/Tests/TestCases.exe. If no window appears, it’s all good!

API

Docopt.fsi

type Docopt.HelpCallback = string -> bool

A simple callback function used by the Docopt.Docopt described below.

new Docopt.Docopt : doc      : string
                  * ?argv    : string array
                  * ?help    : HelpCallback
                  * ?version : obj
                  -> Docopt

The main constructor takes 1 required and 3 optional arguments:

• doc is a string that contains a help message that will be parsed to create the option parser. The syntax of such a help message is given in next sections. For a quick example, you can refer to the first example of this document.

• argv is an optional string array which defaults to System.Environment.GetCommandLineArgs().[1..], the program’s original arguments vector.

• help is an optional HelpCallback help. By default, it just prints the help message (supplied as doc) and exits. If the user-supplied function returns true the program is exited when the function returns; else if the function returns false the -h or --help options can be handled like any other. The argument given to the function is the Usage: part of doc.
  For example, if you want Docopt to ignore these options, you can just do:

  let docopt = Docopt(doc, help=fun _ -> false) in

• version is an optional obj which defaults to a basic System.Object whose ToString() member returns an error. The type of version defines how the version is retrieved:

  • null: Docopt will ignore --version and treat it like a normal option akin to -h and --help above.
  • Lazy<obj>: Docopt will get the version string by invoking version.Value.ToString() on the given lazy value, print it to stdout and exit with exit 0.
  • obj: Docopt will get the version string by invoking version.ToString() on the given object, print it to stdout and exit with exit 0.

This constructor can throw an exception of type UsageException defined as:

exception UsageException of string

if there is a syntax error in the usage patterns. The message carried by the exception describes precisely the error.

member Docopt.Parse : ?argv : string array 
                    * ?args : Arguments.Dictionary 
                    -> Arguments.Dictionary 

The parse method parses the argument vector and stores the results in a Docopt.Arguments.Dictionary instance. It takes 2 optional arguments:

• argv is an optional string array representing the argument vector to be parsed. By default the parsing will be done on the argv Docopt got during its construction.

• args is an optional Docopt.Arguments.Dictionary. It defaults to an empty newly constructed dictionary. The parser will store the results in this, so results will add with existing values.

The return value is a Docopt.Arguments.Dictionary with options, arguments and commands as keys, spelled exactly like in your help message. Informations that were described but not matched will not be in the dictionary (options with [default:...] arguments will still be registered); however accessing them will yield Docopt.Result.None instead of throwing an exception. For instance, if you invoke the top example as:

naval_fate.exe ship Guardian move 100 150 --speed=15

the returned dictionary will be:

Docopt.Arguments.Dictionary [("ship", Flag);
                             ("<name>", Argument "Guardian");
                             ("move", Flag);
                             ("<x>", Argument "100");
                             ("<y>", Argument "150");
                             ("--speed", Argument "15")]

This function can throw an exception of type ArgvException defined as:

exception ArgvException of string

if argv does not satisfy the AST created at construction. The message carried by the exception describes what the error is.

member Docopt.Usage : string

This property contains all the usage parts fused into one string for convenience. Might be slow, as each use calls System.String.Join.

member Docopt.UsageParser : UsageParser

This property allows you to get the UsageParser generated from doc.

Help message format

Help message consists of 2 parts:

• Usage pattern, e.g.:

  Usage: my_program.py [-hso FILE] [--quiet | --verbose] [INPUT ...]
  

• Option descriptions, e.g.:

  -h --help    show this
  -s --sorted  sorted output
  -o FILE      specify output file [default: ./test.txt]
  --quiet      print less text
  --verbose    print more text
  

Their format is described below; other text is ignored.

Usage patterns syntax

This list describes each lexeme in the usage pattern grammar, and exposes the lexeme’s syntax using standard EBNF extended with range ("a"..."z") syntax at the end.
Usage pattern is a substring of doc that starts with usage: (case insensitive) and ends with a visibly empty line. Minimum example:

"""Usage: my_program.exe

"""

The first word after usage: is interpreted as your program’s name. You can specify your program's name several times to signify several exclusive patterns:

"""Usage: my_program.exe FILE
          my_program.exe COUNT FILE

"""

Each pattern can consist of the following elements:

• <lower-case argument> or UPPER-CASE-ARGUMENTS

  Positional arguments. Both form can be used to specify an argument, there is no difference between the two.

  lower_arg_char  = ? any Unicode code point except ">" ? ;
  lower_arg       = "<" , lower_arg_char , { lower_arg_char } , ">" ;
  upper_letter    = ? Unicode category Lu ? ;
  decimal_digit   = ? Unicode category Nd ? ;
  upper_arg_start = upper_letter | decimal_digit ;
  upper_arg_cont  = upper_arg_start | "-" ;
  upper_arg       = upper_arg_start , { upper_arg_cont } ;
  argument        = lower_arg | upper_arg ;

• -o or --option

  Options are typically optional (though this is up to you), and can be either boolean (present/absent), as in --flag, or expect a trailing argument (see next section).

  Short-style options, as in -f, are also allowed. Synonyms between different spellings of the same option (e.g. -v and --verbose) can be established in the option descriptions (see below). Short-style options can also be stacked, as in -rfA. When options are stacked, -rfA is effectively equivalent to (-r | -f | -A)... to the argument parser.

  short_option_char = "a"..."z" | "A"..."Z" | "0"..."9" | "?" ;
  short_option      = "-" , short_option_char , { short_option_char } ;
  long_option_char  = short_option_char | "-" ;
  long_option       = "-" , "-" , long_option_char , { long_option_char } ;

• -aARG or -a ARG or --argument=ARG or --argument ARG

  You can add a trailing argument to a long option. Arguments can be separated from the option name by an = or a single space, and can be specified as <arg> or ARG (consistency of style is recommended, but it is not enforced) .

  You can also add a trailing argument to a short option. In this case, arguments can be separated from the option name or joined to it. As with long options, either style can be used but consistency of style is recommended.

  long_option_arg  = ( "=" | " " ) , argument ;
  short_option_arg = [ " " ] , argument ;
  option           = long_option , [ long_option_arg ]
                   | short_option , [ short_option_arg ]
                   ;

• [] (brackets)

  Patterns inside brackets are optional. [pattern] is exactly equivalent to ε | pattern, with ε the epsilon parser (does absolutely nothing but is always successful).

  brackets = "[" , whitespace , pattern , "]" ;

• () (parens)

  Patterns inside parens are required (the same as patterns not in () are required). Parens are useful if you need to group some elements in subpatterns, either for use with | or ....

  parens = "(" , whitespace , pattern , ")" ;

• | (pipe)

  A pipe | separates mutually exclusive elements in a pattern. The different patterns described by each usage line are also mutually exclusive.

  pipe = pattern , "|" , whitespace , pattern ;

• ... (ellipsis)

  An ellipsis can trail any element or group to make it repeatable once or more. Repeatable elements will be accumulated into a list of occurrences.

  ellipsis = pattern , "..." ;

• [options] (case sensitive)

  The string [options] is a shortcut to match any options specified in your option descriptions.

  options = "[options]" ;

• [-] and [--]

  Single hyphen - is used by convention to specify using stdin as input instead of reading a file.
  Double hyphen -- is typically used to manually separate leading options from trailing positional arguments.

  Both of these are treated as commands, and so are perfectly legal in usage patterns. They are typically optional elements, but can be required if you drop the [].

  single_hyphen = [ "[" ] , "-" , [ "]" ] ;
  double_hyphen = [ "[" ] , "--" , [ "]" ] ;

• commands

  Anything not recognised as something described above is a command (or subcommand).

  command = ? any group of characters surrounded by whitespace ? ;

This gives us the following BNF describing a full usage pattern:

whitespace   = " " | ? tabulation ? ;
newline      = ? newline or eof ? ;
pattern_base = argument
             | option
             | brackets
             | parens
             | pipe
             | ellipsis
             | options
             | single_hyphen
             | double_hyphen
             | command
             ;
pattern      = pattern_base , whitespace ;
program_name = command ;
usage_part   = ? case-insensitive "usage:" ? ;
usage_line   = [ usage_part ] , program_name , { pattern } ;
usage        = { usage_line , newline } ;
grammar      = usage .

If your pattern allows to match argument-less option (a flag) several times:

"""
Usage: my_program.exe [-v | -vv | -vvv]
"""

then number of occurrences of the option will be counted. I.e. args.["-v"] will be Flags(2) if program was invoked as my_program.exe -vv. Same works for commands.

If your usage patterns allows to match same-named option with argument or positional argument several times, the matched arguments will be collected into a list:

"""
Usage: my_program.py <file> <file> --path=<path>...
"""

I.e. invoked with my_program.exe file1 file2 --path=./here --path=./there the returned dictionary will be:

Docopt.Arguments.Dictionary [("<file>", Arguments ["file1";"file2"]);
                             ("--path", Arguments ["./here";"./there"])]

Option descriptions format

Option descriptions consist of a list of options that you put below your usage patterns.

It is necessary to list option descriptions in order to specify:

• synonymous short and long options,
• if an option has an argument,
• if option's argument has a default value.

The rules are as follows:

• Every line in doc that starts with - or -- (not counting spaces) is treated as an option description, e.g.:

  Options:
    --verbose   # GOOD
    -o FILE     # GOOD
  Other: --bad  # BAD, line does not start with dash "-"
  

• To specify that option has an argument, put a word describing that argument after space (or equals "=" sign) as shown below. Follow either or UPPERCASE convention for options' arguments. You can use comma if you want to separate options. In the example below, both lines are valid, however you are recommended to stick to a single style.:

  -o FILE --output=FILE       # without comma, with "=" sign
  -i <file>, --input <file>   # with comma, without "=" sing
  

  Here is a BNF for this:

  option_desc_short = whitespace , [ short_option ] ;
  option_desc_long  = whitespace , [ long_option ] ;
  option_desc_both  = option_desc_short , [ "," ] , " " , long_option ;
  option_desc       = option_desc_short
                    | option_desc_long
                    | option_desc_both
                    ;
  option_desc_line  = option_part , ( "  " , ? text ? | whitespace ) , newline ;

  You should get the DFA for unambigous (and easier) parsing.

• Use two spaces to separate options with their informal description:

  --verbose More text.   # BAD, will be treated as if verbose option had
                         # an argument "More", so use 2 spaces instead
  -q        Quit.        # GOOD
  -o FILE   Output file. # GOOD
  --stdout  Use stdout.  # GOOD, 2 spaces
  

• If you want to set a default value for an option with an argument, put it into the option-description, in form [default: <my-default-value>]:

  --coefficient=K  The K coefficient [default: 2.95]
  --output=FILE    Output file [default: test.txt]
  --directory=DIR  Some directory [default: ./]
  

---

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Changelog

The first stable release will be v1.0. Until then, use with caution as things might change drastically.

• 0.1.0 - 29/01/2016 First release. All reference language agnostic tests pass.

Notes

Pull requests welcome!
If you see a typo, or something wrong in the documentation, feel free to submit one too!

What’s next

• Option to exit automatically on help or version
• [--] token
• options_first parameter
• Active patterns for result dictionary
• Code cleanup
• Comments
• Type provider?
• Typed arguments?