Module Command.Spec

module Spec: sig .. end

composable command-line specifications

command parameters

type 'a param

specification of an individual parameter to the command's main function

val const : 'a -> 'a param

a hard-coded parameter

val map : 'a param -> f:('a -> 'b) -> 'b param

parameter transformation

various internal values

val help : string Core_kernel.Std.Lazy.t param

the help text for the command

val path : string list param

the subcommand path of the command

val args : string list param

the arguments passed to the command

command specifications

type ('main_in, 'main_out) t

composable command-line specifications

Ultimately one forms a base command by combining a spec of type ('main, unit) t with a main function of type 'main; see the basic function below. Combinators in this library incrementally build up the type of main according to what command-line parameters it expects, so the resulting type of main is something like:

arg1 -> ... -> argN -> unit

It may help to think of ('a, 'b) t as a function space 'a -> 'b embellished with information about:

how to parse command line
what the command does and how to call it
how to auto-complete a partial command line

One can view a value of type ('main_in, 'main_out) t as function that transforms a main function from type 'main_in to 'main_out, typically by supplying some arguments. E.g. a value of type Spec.t might have type:

       (arg1 -> ... -> argN -> 'r, 'r) Spec.t

Such a value can transform a main function of type arg1 -> ... -> argN -> 'r by supplying it argument values of type arg1, ..., argn, leaving a main function whose type is 'r. In the end, Command.basic takes a completed spec where 'r = unit, and hence whose type looks like:

        (arg1 -> ... -> argN -> unit, unit) Spec.t

A value of this type can fully apply a main function of type arg1 -> ... -> argN -> unit to all its arguments.

The view of ('main_in, main_out) Spec.t as a function from 'main_in to 'main_out is directly reflected by the step function, whose type is:

        val step : ('m1 -> 'm2) -> ('m1, 'm2) t

spec1 ++ spec2 ++ ... ++ specN composes spec1 through specN.

For example, if spec_a and spec_b have types:

        spec_a: (a1 -> ... -> aN -> 'ra, 'ra) Spec.t
        spec_b: (b1 -> ... -> bM -> 'rb, 'rb) Spec.t

then spec_a ++ spec_b has the following type:

        (a1 -> ... -> aN -> b1 -> ... -> bM -> 'rb, 'rb) Spec.t

So, spec_a ++ spec_b transforms a main function it by first supplying spec_a's arguments of type a1, ..., aN, and then supplying spec_b's arguments of type b1, ..., bm.

One can understand ++ as function composition by thinking of the type of specs as concrete function types, representing the transformation of a main function:

        spec_a: \/ra. (a1 -> ... -> aN -> 'ra) -> 'ra
        spec_b: \/rb. (b1 -> ... -> bM -> 'rb) -> 'rb

Under this interpretation, the composition of spec_a and spec_b has type:

        spec_a ++ spec_b : \/rc. (a1 -> ... -> aN -> b1 -> ... -> bM -> 'rc) -> 'rc

And the implementation is just function composition:

        sa ++ sb = fun main -> sb (sa main)

val empty : ('m, 'm) t

the empty command-line spec

val (++) : ('m1, 'm2) t ->
       ('m2, 'm3) t -> ('m1, 'm3) t

command-line spec composition

val (+>) : ('m1, 'a -> 'm2) t ->
       'a param -> ('m1, 'm2) t

add a rightmost parameter onto the type of main

val (+<) : ('m1, 'm2) t ->
       'a param -> ('a -> 'm1, 'm2) t

add a leftmost parameter onto the type of main

this function should only be used as a workaround in situations where the order of composition is at odds with the order of anonymous arguments due to factoring out some common spec

val step : ('m1 -> 'm2) -> ('m1, 'm2) t

combinator for patching up how parameters are obtained or presented

Here are a couple examples of some of its many uses

introducing labeled arguments

step (fun m v -> m ~foo:v)
               +> flag "-foo" no_arg : (foo:bool -> 'm, 'm) t

prompting for missing values

step (fun m user -> match user with
                 | Some user -> m user
                 | None -> print_string "enter username: "; m (read_line ()))
               +> flag "-user" (optional string) ~doc:"USER to frobnicate"
               : (string -> 'm, 'm) t

A use of step might look something like:

        step (fun main -> let ... in main x1 ... xN) : (arg1 -> ... -> argN -> 'r, 'r) t

Thus, step allows one to write arbitrary code to decide how to transform a main function. As a simple example:

        step (fun main -> main 13.) : (float -> 'r, 'r) t

This spec is identical to const 13.; it transforms a main function by supplying it with a single float argument, 13.. As another example:

        step (fun m v -> m ~foo:v) : (foo:'foo -> 'r, 'foo -> 'r) t

This spec transforms a main function that requires a labeled argument into a main function that requires the argument unlabeled, making it easily composable with other spec combinators.

val wrap : (run:('m1 -> 'r1) -> main:'m2 -> 'r2) ->
       ('m1, 'r1) t -> ('m2, 'r2) t

combinator for defining a class of commands with common behavior

Here are two examples of command classes defined using wrap

print top-level exceptions to stderr

wrap (fun ~run ~main ->
                 Exn.handle_uncaught ~exit:true (fun () -> run main)
               ) : ('m, unit) t -> ('m, unit) t

iterate over lines from stdin

wrap (fun ~run ~main ->
                 In_channel.iter_lines stdin ~f:(fun line -> run (main line))
               ) : ('m, unit) t -> (string -> 'm, unit) t

argument types

module Arg_type: sig .. end

val string : string Arg_type.t

val int : int Arg_type.t

val float : float Arg_type.t

val bool : bool Arg_type.t

val date : Date.t Arg_type.t

val time_span : Span.t Arg_type.t

val file : string Arg_type.t

flag specifications

type 'a flag

a flag specification

val flag : ?aliases:string list ->
       string -> 'a flag -> doc:string -> 'a param

flag name spec ~doc specifies a command that, among other things, takes a flag named name on its command line. doc indicates the meaning of the flag.

NOTE: the doc for a flag which takes an argument should be of the form arg_name ^ " " ^ description where arg_name describes the argument and description describes the meaning of the flag.

NOTE: flag names (including aliases) containing underscores will be rejected. Use dashes instead.

val required : 'a Arg_type.t -> 'a flag

required flags must be passed exactly once

val optional : 'a Arg_type.t -> 'a option flag

optional flags may be passed at most once

val optional_with_default : 'a -> 'a Arg_type.t -> 'a flag

optional_with_default flags may be passed at most once, and default to a given value

val listed : 'a Arg_type.t -> 'a list flag

listed flags may be passed zero or more times

val no_arg : bool flag

no_arg flags may be passed at most once. The boolean returned is true iff the flag is passed on the command line

val no_arg_register : key:'a Core_kernel.Std.Univ_map.With_default.Key.t ->
       value:'a -> bool flag

no_arg_register ~key ~value is like no_arg, but associates value with key in the in the auto-completion environment

val no_arg_abort : exit:(unit -> Core_kernel.Std.never_returns) -> unit flag

no_arg_abort ~exit is like no_arg, but aborts command-line parsing by calling exit. This flag type is useful for "help"-style flags that just print something and exit.

val escape : string list option flag

escape flags may be passed at most once. They cause the command line parser to abort and pass through all remaining command line arguments as the value of the flag.

val flags_of_args_exn : Core_kernel.Std.Arg.t list -> ('a, 'a) t

flags_of_args_exn args creates a spec from Arg.ts, for compatibility with ocaml's base libraries. Fails if it encounters an arg that cannot be converted.

NOTE: There is a difference in side effect ordering between Arg and Command. In the Arg module, flag handling functions embedded in Arg.t values will be run in the order that flags are passed on the command line. In the Command module, using flags_of_args_exn flags, they are evaluated in the order that the Arg.t values appear in flags.

anonymous argument specifications

type 'a anons

a specification of some number of anonymous arguments

val anon : 'a anons -> 'a param

anon spec specifies a command that, among other things, takes the anonymous arguments specified by spec.

val (%:) : string -> 'a Arg_type.t -> 'a anons

(name %: typ) specifies a required anonymous argument of type typ.

The name must not be surrounded by whitespace, if it is, an exn will be raised.

If the name is surrounded by a special character pair (<>, {}, [] or (),) name will remain as-is, otherwise, name will be uppercased.

In the situation where name is only prefixed or only suffixed by one of the special character pairs, or different pairs are used, (e.g. "<ARG]") an exn will be raised.

The (possibly transformed) name is mentioned in the generated help for the command.

val sequence : 'a anons -> 'a list anons

sequence anons specifies a sequence of anonymous arguments. An exception will be raised if anons matches anything other than a fixed number of anonymous arguments

val maybe : 'a anons -> 'a option anons

(maybe anons) indicates that some anonymous arguments are optional

val maybe_with_default : 'a -> 'a anons -> 'a anons

(maybe_with_default default anons) indicates an optional anonymous argument with a default value

t2, t3, and t4 each concatenate multiple anonymous argument specs into a single one. The purpose of these combinators is to allow for optional sequences of anonymous arguments. Consider a command with usage:

        main.exe FOO [BAR BAZ]

where the second and third anonymous arguments must either both be there or both not be there. This can be expressed as:

        t2 ("FOO" %: foo) (maybe (t2 ("BAR" %: bar) ("BAZ" %: baz)))]

Sequences of 5 or more anonymous arguments can be built up using nested tuples:

        maybe (t3 a b (t3 c d e))

val t2 : 'a anons ->
       'b anons -> ('a * 'b) anons

val t3 : 'a anons ->
       'b anons ->
       'c anons -> ('a * 'b * 'c) anons

val t4 : 'a anons ->
       'b anons ->
       'c anons ->
       'd anons -> ('a * 'b * 'c * 'd) anons