On Mon, Jul 02, 2001 at 08:17:58PM -0500 or so it is rumoured hereabouts,
Jeff Dike thought:
> [EMAIL PROTECTED] said:
> > Now that's interesting. So how do I tokenise the strings?
>
> OK, let's say you have an interpreted language, and a program being
> interpreted has this in an inner loop:
> foo;
> bar;
> baz;
>
> If you represent pieces of this program with strings, you'll end up with an
> array like [ "foo", "bar", "baz" ] for that loop body.
>
> The interpreter will need to do something like this for each iteration of that
> loop:
> if(!strcmp(instruction, "foo")) do_foo();
> else if(!strcmp(instruction, "bar")) do_bar();
> else if(!strcmp(instruction, "baz")) do_baz();
> else if(!strcmp(instruction, "hoo")) do_hoo();
> else if(!strcmp(instruction, "ha")) do_ha();
>
> which will be slow.
>
> So, what's normally done instead is that when the program is read in, a
> conversion like this happens:
> "foo;" -> FOO_INSTR
> "bar;" -> BAR_INSTR
> "baz;" -> BAZ_INSTR
So, I can do something like:
#define FORCE_SWITCH "--force"
#define CONFIG_SWITCH "-C"
and so on?
> where *_INSTR are #defined constants or enum constants.
>
> So, now the inner loop is represented as this array :
> [ FOO_INSTR, BAR_INSTR, BAZ_INSTR]
>
> And the interpreter can be implemented using a switch:
>
> switch(instruction){
> case FOO_INSTR:
> do_foo();
> break;
> case BAR_INSTR:
> do_bar();
> break;
and
case FORCE_SWTICH:
force=1;
break;
case CONFIG_SWITCH:
strcpy(config_file_name, argv[2]);
break;
> which will be a lot faster.
>
> Jeff
Conor
--
Conor Daly <[EMAIL PROTECTED]>
Domestic Sysadmin :-)
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