A small mod now allows this:
Shell::system("ls","-lasp");
Shell::system("ls");
Shell::system ("ls","-lasp","*.flx");
What's the big deal?
An apparent variable number of arguments!
Really?
Heck NO, Felix doesn't support that. No, what we have is:
gen system[T with Streamable[T,string]] (args:T) : int =
{
var lst = Empty[string];
for arg in args do
lst = lst + arg;
done
return system args;
}
So we're using an iterator method (implicit in the for loop) to access
an arbitrary Streamable (any data structure with an iterator method).
Lists are Steamable, and we're making one, but the return statement
calls
// list of string argument
gen system (args:list[string]) : int =>
args.create_system_command.system
;
because it is more specialised. That quotes the arguments
and in turn calls:
// string argument
gen system (cmd:string) = {
if Env::getenv "FLX_SHELL_ECHO" != "" do
eprintln$ "[system] " + cmd;
done
return basic_system cmd;
}
Note "string" is a Streamable too: it's a stream of chars.
So watch out! But this one is more specialised. And it calls
//$ basic command with line quoting.
gen basic_system (cmd: string) :int =>
cmd.quote_line_for_system.raw_system
;
which in turn calls:
//$ System command is ISO C and C++ standard.
gen raw_system: string -> int = "::std::system($1.c_str())"
requires Cxx_headers::cstdlib
;
i will note in passing 'bash' is a piece of crap and the third call
in the original text won't work because quoted wildcards aren't
expanded. $ENV_IRON_MENT variables are expanded in double
quotes. If we use \ quoting instead of quote marks, * wildcards
are expanded which is no good if we're trying to pass a regex
containing a *. The bottom line is that "transparent" shell calling
is impossible by definition because we cannot distinguish between
wildcards to be expanded and those which are not.
HOWEVER the real point is yet to be made! How do we get the
variable length arguments?
The answer is:
("hello", "world")
is a tuple of strings which is an array of length 2 which is a Streamable.
As you know Felix doesn't have dynamic typing (as such), but this
is very scripting language like.. something about quacking like
ducks comes to mind ..
--
john skaller
skal...@users.sourceforge.net
http://felix-lang.org
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