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 <s-expression>)
| (help <string> <s-expression>)
|
Each elements of list are match against the rules. If one
of these matches, args-parse proceeds as follows:
- The matched argument elements of
list are removed from the list.
- The
<s-expression> associated to the matching rule
is evaluated in an environment where the rule variables are bound.
- 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 fmt | bigloo 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, the pseudo-variable
else is bound to the first unmatched argument and the pseudo-variable
rest is bound to all the unmatched arguments.
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))))
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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
|