Spec (core.Core__Command.Spec)

include Param.S with type a t := a param

type +'a t

Command.Param is intended to be used with the %map_open syntax defined in ppx_let, like so:


          let command =
            Command.basic' ~summary:"..."
              [%map_open
                let count  = anon ("COUNT" %: int)
                and port   = flag "port" (optional int) ~doc:"N listen on this port"
                and person = person_param
                in
                (* ... command-line validation code, if any, goes here ... *)
                fun () ->
                  (* the body of the command *)
                  do_stuff count port person
              ]

One can also use %map_open to define composite command line parameters, like person_param in the previous snippet:


          type person = { name : string; age : int }

          let person_param : person Command.Param.t =
            [%map_open
              let name = flag "name" (required string) ~doc:"X name of the person"
              and age  = flag "age"  (required int)    ~doc:"N how many years old"
              in
              {name; age}
            ]

The right hand sides of %map_open definitions have Command.Param in scope.

Alternatively, you can say:


          let open Foo.Let_syntax in
          [%map_open
            let x ...
          ]

if Foo follows the same conventions as Command.Param.

See example/command/main.ml for more examples.

include Core__.Import.Applicative.S with type a t := a t

type 'a t

val return : 'a ‑> 'a t

val apply : ('a ‑> 'b) t ‑> 'a t ‑> 'b t

val map : 'a t ‑> f:('a ‑> 'b) ‑> 'b t

val map2 : 'a t ‑> 'b t ‑> f:('a ‑> 'b ‑> 'c) ‑> 'c t

val map3 : 'a t ‑> 'b t ‑> 'c t ‑> f:('a ‑> 'b ‑> 'c ‑> 'd) ‑> 'd t

val all : 'a t list ‑> 'a list t

val all_ignore : unit t list ‑> unit t

val both : 'a t ‑> 'b t ‑> ('a * 'b) t

module Applicative_infix : sig ... end

include module type of Applicative_infix

val (<*>) : ('a ‑> 'b) t ‑> 'a t ‑> 'b t

same as apply

val (<*) : 'a t ‑> unit t ‑> 'a t

val (*>) : unit t ‑> 'a t ‑> 'a t

various internal values

val help : string Core__.Import.Lazy.t t

the help text for the command

val path : string list t

the subcommand path of the command

val args : string list t

the arguments passed to the command

val flag : ?aliases:string list ‑> ?full_flag_required:unit ‑> string ‑> 'a Flag.t ‑> doc:string ‑> 'a t

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.

All flags must have a dash at the beginning of the name. If name is not prefixed by "-", it will be normalized to "-" ^ name.

Unless full_flag_required is used, one doesn't have to pass name exactly on the command line, but only an unambiguous prefix of name (i.e., a prefix which is not a prefix of any other flag's name).

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.

NOTE: "-" by itself is an invalid flag name and will be rejected.

val anon : 'a Anons.t ‑> 'a t

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

val choose_one : 'a option t list ‑> if_nothing_chosen:[ `Default_to of 'a | `Raise ] ‑> 'a t

choose_one clauses ~if_nothing_chosen expresses a sum type. It raises if more than one of clauses is Some _. When if_nothing_chosen = `Raise, it also raises if none of clauses is Some _.

val const : 'a ‑> 'a param

Superceded by return, preserved for backwards compatibility

val pair : 'a param ‑> 'b param ‑> ('a * 'b) param

Superceded by both, preserved for backwards compatibility

command specifications

type (-'main_in, +'main_out) t

composable command-line specifications

Ultimately one forms a basic command by combining a spec of type ('main, unit -> 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 -> 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 -> unit, and hence whose type looks like:


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

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

The final unit argument allows the implementation to distinguish between the phases of (1) parsing the command line and (2) running the body of the command. Exceptions raised in phase (1) lead to a help message being displayed alongside the exception. Exceptions raised in phase (2) are displayed without any command line help.

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

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:

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

module Arg_type : module type of Arg_type with type 'a Arg_type.t = 'a Arg_type.t

include module type of Arg_type.Export

val string : string Arg_type.t

val int : int Arg_type.t

Beware that an anonymous argument of type int cannot be specified as negative, as it is ambiguous whether -1 is a negative number or a flag. (The same applies to float, time_span, etc.) You can use the special built-in "-anon" flag to force a string starting with a hyphen to be interpreted as an anonymous argument rather than as a flag, or you can just make it a parameter to a flag to avoid the issue.

val char : char Arg_type.t

val float : float Arg_type.t

val bool : bool Arg_type.t

val date : Core__.Import.Date.t Arg_type.t

val percent : Core__.Import.Percent.t Arg_type.t

val time : Core__.Import_time.Time.t Arg_type.t

val time_ofday : Core__.Import_time.Time.Ofday.Zoned.t Arg_type.t

requires a time zone

val time_ofday_unzoned : Core__.Import_time.Time.Ofday.t Arg_type.t

for when zone is implied

val time_zone : Core__.Import_time.Time.Zone.t Arg_type.t

val time_span : Core__.Import_time.Time.Span.t Arg_type.t

val file : string Arg_type.t

uses bash autocompletion

val host_and_port : Core__.Import.Host_and_port.t Arg_type.t

val ip_address : Unix.inet_addr Arg_type.t

val sexp : Core__.Import.Sexp.t Arg_type.t

val sexp_conv : (Core__.Import.Sexp.t ‑> 'a) ‑> 'a Arg_type.t

type 'a flag = 'a Flag.t

a flag specification

include module type of Flag with type a Flag.t := a flag

flag specifications

type 'a t

val required : 'a Arg_type.t ‑> 'a t

required flags must be passed exactly once

val optional : 'a Arg_type.t ‑> 'a option t

optional flags may be passed at most once

val optional_with_default : 'a ‑> 'a Arg_type.t ‑> 'a t

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

val listed : 'a Arg_type.t ‑> 'a list t

listed flags may be passed zero or more times

val one_or_more : 'a Arg_type.t ‑> ('a * 'a list) t

one_or_more flags must be passed one or more times

val no_arg : bool t

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__.Import.Univ_map.With_default.Key.t ‑> value:'a ‑> bool t

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__.Import.never_returns) ‑> unit t

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 t

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.

A standard choice of flag name to use with escape is "--".

val map_flag : 'a flag ‑> f:('a ‑> 'b) ‑> 'b flag

map_flag flag ~f transforms the parsed result of flag by applying f

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

flags_of_args_exn args creates a spec from Caml.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 Caml.Arg and Command. In the Arg module, flag handling functions embedded in Caml.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 Caml.Arg.t values appear in flags.

type 'a anons = 'a Anons.t

a specification of some number of anonymous arguments

include module type of Anons with type a Anons.t := a anons

anonymous argument specifications

type +'a t

a specification of some number of anonymous arguments

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

(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 t ‑> 'a list t

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 non_empty_sequence_as_pair : 'a t ‑> ('a * 'a list) t

non_empty_sequence_as_pair anons and non_empty_sequence_as_list anons are like sequence anons except that an exception will be raised if there is not at least one anonymous argument given.

val non_empty_sequence_as_list : 'a t ‑> 'a list t

val maybe : 'a t ‑> 'a option t

(maybe anons) indicates that some anonymous arguments are optional

val maybe_with_default : 'a ‑> 'a t ‑> 'a t

(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 t ‑> 'b t ‑> ('a * 'b) t

val t3 : 'a t ‑> 'b t ‑> 'c t ‑> ('a * 'b * 'c) t

val t4 : 'a t ‑> 'b t ‑> 'c t ‑> 'd t ‑> ('a * 'b * 'c * 'd) t

Module Core__Command.Spec

older interface for command-line specifications

command parameters

various internal values

command specifications

flag specifications

anonymous argument specifications