14. Bigloo -- Command Line Parsing

14. Bigloo -- Command Line Parsing

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Home: Bigloo
A ``practical Scheme compiler''
User manual for version 2.6c
March 2004

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Chapters

  Acknowledgements
1. Table of contents
2. Overview of Bigloo
3. Modules
4. Core Language
5. Standard Library
6. Pattern Matching
7. Object System
8. Threads
9. Regular parsing
10. Lalr(1) parsing
11. Errors and Assertions
12. Eval and code interpretation
13. Macro expansion
14. Command Line Parsing
15. Explicit typing
16. The C interface
17. The Java interface
18. Bigloo Libraries
19. Extending the Runtime System
20. SRFIs
21. DSSSL support
22. Compiler description
23. User Extensions
24. Bigloo Development Environment
25. Global Index
26. Library Index
  Bibliography

Bigloo supports command line argument parsing. That is, when an application is spawn from an Unix shell, the main function is called and its argument is bound to the list of the command line arguments, See Module declaration. The args-parse form may be used to parse these.

args-parse list rules [null-rule] [else-rule] ...bigloo syntax
The argument list is a list of strings. Rules is defined by the following grammar:

<rule>      ==> (section <string>)
              | ((<option> <help>) <s-expression>)
              | ((<option>) <s-expression>)
              | ((<flag> <var> <var> ...) <s-expression>)
              | ((<flag> <var> <var> ... <help>) <s-expression>)
<null-rule> ==> (() <s-expression>)
<else-rule> ==> (else <s-expression>)
<option>    ==> <flag>
              | <string><var>
<flag>      ==> <string>
              | (<string>+)
<var>       ==> an identifier leaded by the ? character
<help>      ==> (help <string>)
              | (help <string> <string>)
Each elements of list are match against the rules. If one of these matches, args-parse proceeds as follows:

  1. The matched argument elements of list are removed from the list.
  2. The <s-expression> associated to the matching rule is evaluated in an environment where the rule variables are bound.
  3. The argument parsing is resumed with the rest of list.

In addition to parsing the command line arguments, args-parse enables help message printing.

args-parse-usage fmtbigloo procedure
This is a procedure of one argument, an boolean. Args-parse-usage constructs an help message from all the option described in a args-parse form. Args-parse-usage is only defined in the <s-expression> of an args-parse form.

At last, if no rule matches an argument and if the args-parse form contains an else rule, this is evaluated. In the <s-expression> part of that rule, a pseudo-variable else is bound to the unmatched argument.

Here is an example of argument parsing deploying all the possible rules:

(module args-example
   (main main))

(define (main argv)
   (args-parse (cdr argv)
      (section "Help")
      (("?")
       (args-parse-usage #f))
      ((("-h" "--help") (help "?,-h,--help" "This help message"))
       (args-parse-usage #f))
      (section "Misc")
      ((("-v" "--version") (help "Version number"))
       (print *version*))
      (("-o" ?file (help "The output file"))
       (set! *dest* file))
      (("--input=?file" (help "The input file"))
       (set! *input* file))
      (else
       (print "Illegal argument `" else "'. Usage:")
       (args-parse-usage #f))))
Invoking the compiled args-example module could produce:

> bigloo.new args.scm
args.scm:
> a.out toto        
Illegal argument `toto'. Usage:

Help:
   ?,-h,--help    --  This help message

Misc:
   -v,--version   --  Version number
   -o <file>      --  The output file
   --input=<file> --  The input file



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Last update Tue Mar 16 17:05:46 2004