Re: Labels and operators

[Markus Mottl <mottl@miss.wu-wien.ac.at>]

On Mon, 19 Jun 2000, John Prevost wrote:
> A friend of mine recently said "if ML had regexp stuff that was as
> convenient as Perl, I'd switch to it for everything", and mentioned =~
> as something he specifically wanted.  So, as I was walking home
> tonight, I thought "hey, I bet I could make some little operators for
> the PCRE library and show him!"

The "=~"-operator itself, as it is normally used in Perl for matching,
is fairly easy to replicate:

  let (=~) str pat = Pcre.pmatch ~pat str

  let _ =
    print_endline (if read_line () =~ "foo" then "has foo!" else "no foo!")

> But, it also occurred to me that you want to use the nice labelled
> optional argument stuff, and I wasn't sure you could do that with
> operators.  Here's what I've discovered.

Well, sometimes we are really struck by the only "two-dimensional" way
in which we can write our sources (top-down + left-right). If we could
write into the depth, there would be an elegant solution for adding
arguments to infix operators...

> The only solution I can think of is something like:
[snip]
> # "foo" =~ re "f";;
> - : bool = true
> # "foo" =~ re "f" ~pos:1;;
> - : bool = false
> 
> Which, well, works, but seems kind of nasty.

I normally try to avoid new operators, but if I wanted to have a somewhat
"powered up" version of "=~", your version here would look fine to me -
just read every piece aloud:

  "foo"      =~                re              "f"       ~pos:1
  "foo" - is matched by - regular expression - "f" - at position one

This is pretty close to the human way of expressing things. (Larry Wall,
the linguist, would be proud of you! ;-)

> since the labelled args could not in any way shape or form be thought
> to go with either expr1 or expr2.  This would lead to things like:
> 
> # "foo" =~ ~pos:1 "f";;
> - : bool = false
> 
> being possible.  Don't know whether it's a great idea, though.

I prefer your first version: "subject", "verb" and "object" are close
together, the additional modifiers only follow afterwards. To my
knowledge, most natural languages would order expressions like this.

Best regards,
Markus Mottl

-- 
Markus Mottl, mottl@miss.wu-wien.ac.at, http://miss.wu-wien.ac.at/~mottl