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+(* 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 four 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 ([cmd] is assumed to be the command name):
+
+-   [cmd -flag           ](a unit option)
+-   [cmd -int 1          ](an int option with argument [1])
+-   [cmd -string foobar  ](a string option with argument ["foobar"])
+-   [cmd -float 12.34    ](a float option with argument [12.34])
+-   [cmd 1 2 3           ](three anonymous arguments: ["1"], ["2"], and ["3"])
+-   [cmd 1 2 -flag 3 -string bar 4]
+-   [                    ](four anonymous arguments, a unit option, and
+-   [                    ] a string option with argument ["bar"])
+*)
+
+type spec =
+    String of (string -> unit)
+  | Int of (int -> unit)
+  | Unit of (unit -> unit)
+  | Float of (float -> 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. *)
+
+exception Bad of string
+        (* Functions in [speclist] or [anonfun] can raise [Bad] with
+           an error message to reject invalid arguments. *)