(* Parsing of command line arguments. *) (* This module provides a general mechanism for extracting options and   arguments from the command line to the program. *)(* Syntax of command lines.    A keyword is a character string starting with a [-].    An option is a keyword alone or followed by an argument.    There are 4 types of keywords: Unit, String, Int, and Float.    Unit keywords do not take an argument.    String, Int, and Float keywords take the following word on the command line    as an argument.    Arguments not preceded by a keyword are called anonymous arguments.     Examples ([foo] is assumed to be the command name): -   [foo -flag           ](a unit option)-   [foo -int 1          ](an int option with argument [1])-   [foo -string foobar  ](a string option with argument ["foobar"])-   [foo -real 12.34    ](a real option with argument [12.34])-   [foo 1 2 3           ](three anonymous arguments: ["1"], ["2"], and ["3"])-   [foo 1 2 -flag 3 -string bar 4]-   [                    ](four anonymous arguments, a unit option, and-   [                    ] a string option with argument ["bar"])*) datatype spec =    String  of (string -> unit)  | Int     of (int -> unit)  | Unit    of (unit -> unit)  | Real    of (real -> unit); (*    The concrete type describing the behavior associated with a keyword.*) val parse : (string * spec) list -> (string -> unit) -> unit;(*    [parse speclist anonfun]    parses the command line, calling the functions in [speclist]    whenever appropriate, and [anonfun] on anonymous arguments.    The functions are called in the same order as they appear on the command    line.    The strings in the [(string * spec) list] are keywords and must    start with a [-], else they are ignored.    For the user to be able to specify anonymous arguments starting with a    [-], include for example [("--", String anonfun)] in [speclist].*) exception Bad of string (*    Functions in [speclist] or [anonfun] can raise [Bad message]    to reject invalid arguments.*)