[[tags: egg]]

== easy-args

[[toc:]]

=== Description

Handle command-line arguments as parameter objects.

=== Author

[[Evan Hanson]]

=== Documentation

{{easy-args}} provides a simple way to handle command-line arguments as
parameter objects.

It is intended to be easy to use for small binaries and one-off
scripts. For more complete option handling and usage message utilities,
see [[/eggref/4/args|args]], [[/eggref/4/getopt-long|getopt-long]],
[[/eggref/4/srfi-37|srfi-37]], or [[/eggref/4/usage|usage]].

==== define-arguments

<syntax>(define-arguments (name [value [guard]]) ...)</syntax>

{{define-arguments}} creates parameter objects for the given command
line option names and sets them according to the application's
{{command-line-arguments}} parameter.

For each specified argument, {{name}} should be an identifier and will
be bound to the newly-created parameter object. {{value}}, if given,
must be a boolean, string, number or symbol and will be the default value
of the parameter object. If no {{value}} is given, {{#f}} is used. If
a procedure {{guard}} is given, it is used as the parameter object's
conversion procedure.

This form reads Chicken's {{command-line-arguments}} parameter internally,
setting any matching parameter objects to the specified values and
removing handled arguments from the list. Matched boolean arguments
are set to {{#t}}; other arguments are set to the value following the
matched argument's flag.

{{name}}, when prefixed by a single dash ("-"), is used as the argument's
command-line flag. If {{name}} contains asterisks ("*"), they are stripped
from the flag.

{{define-arguments}} renames the original {{command-line-arguments}}
object to {{command-line-arguments*}}. Its return value is undefined.

=== Examples

<enscript highlight="scheme">
(use easy-args extras)

(define-arguments
  (all-caps)
  (prompt "Your name? ")
  (exclamations 1))

(display (prompt))

(let ((message (string-join `("Hello," ,(read-line)))))
  (if (all-caps)
    (display (string-upcase message))
    (display message)))

(print (make-string (exclamations) #\!))
</enscript>

With the file above as {{greeter.scm}}:

  $ csc greeter.scm
  
  $ ./greeter
  Your name? [Henrietta]
  Hello, Henrietta!
  
  $ ./greeter -all-caps
  Your name? [Henrietta]
  HELLO, HENRIETTA!
  
  $ ./greeter -prompt "Name: " -exclamations 3
  Name: [Henrietta]
  Hello, Henrietta!!!

=== History

* 0.4 Allow symbols, stash original c-l-a
* 0.3 Fix scoping for newer chickens
* 0.2 Rewrite as single form
* 0.1 Initial release

=== License

  Copyright (c) 2011, Evan Hanson All rights reserved.
  
  Redistribution and use in source and binary forms, with or without
  modification, are permitted provided that the following conditions
  are met:
  
  * Redistributions of source code must retain the above copyright
  notice, this list of conditions and the following disclaimer.  *
  Redistributions in binary form must reproduce the above copyright
  notice, this list of conditions and the following disclaimer in the
  documentation and/or other materials provided with the distribution.
  * Neither the name of the author nor the names of its contributors
  may be used to endorse or promote products derived from this software
  without specific prior written permission.
  
  THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER AND CONTRIBUTORS
  "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
  A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
  HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
  LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.