Path: utzoo!mnetor!uunet!lll-winken!lll-lcc!ames!elroy!devvax!lwall
From: lwall@devvax.JPL.NASA.GOV (Larry Wall)
Newsgroups: comp.sources.d
Subject: Re: How are YOU using perl?
Message-ID: <1876@devvax.JPL.NASA.GOV>
Date: 22 Apr 88 19:11:00 GMT
References: <235@ateng.UUCP> <42400006@uicsrd.csrd.uiuc.edu>
Reply-To: lwall@devvax.JPL.NASA.GOV (Larry Wall)
Organization: Jet Propulsion Laboratory, Pasadena, CA.
Lines: 68

In article <42400006@uicsrd.csrd.uiuc.edu> mcdaniel@uicsrd.csrd.uiuc.edu writes:
:
: 1) there is no way to declare local names.  To avoid name collisions
: in "sub"s I was prefixing names with the "sub" name, which lead to
: lines like
: 
: 	for ($SWAP_i = 0; $SWAP_i < $#lru_buffers; $SWAP_i++)

I agree, that's painful.  Currently I'd use pushes and pops to make local
variables, but I'm planning to make a "local" operator of some sort.
For now:

	sub FOO {
	    push(@STK,$i,$j,$k);
	    ...
	    ($k,$j,$i) = (pop(@STK), pop(@STK), pop(@STK));
	}

But someday soon:

	sub FOO {
	    local($i,$j,$k);
	    ...
	}

All it does internally, of course, is to push $i, $j and $k on a stack,
and restore them automatically upon exiting the block in which they are pushed.
The local operator would probably be an lvalue, so you could say

	sub FOO {
	    local($x, $y, $z) = @_;	# name formal parms
	    local($i, $j, $k);		# push locals
	    ...
	}

Can you think of a better way to do this?

: 2) If I make a typo in a variable name, I get no compiler- or run-time
: notice except for wrong answers.  Icon has a partial solution: an
: option makes all new variables start with a special <undefined> value,
: which causes a run-time error if used before setting.  This gets many
: of the cases, but you can still sometimes use a typo-ed name on the
: LHS of an assignment without warning.  Only declarations can catch
: those.

It will be fairly easy to add a similar option to perl.  In fact, it'll take
about 10 minutes.

How about a warning on variables that are only mentioned once, either as
lvalue or rvalue?  Probably tied to the same option.  How about -w for "warn"?

: For a short program, all the identifiers are there in front of you,
: and it's easier to see and avoid such problems.  Furthermore, perl's
: typelessness (which I like) and lack of declarations help---you can
: get off the ground without all the overhead of typing (in either
: meaning of the word).  But after 175 lines of perl, I decided that
: putting up with C (despite mucking about with <string.h> and sscanf
: and malloc and pointers and . . .) was easier.
: 
: However, I *will* use perl in shorter applications.

Perl isn't intended for long applications.  You'll note that I write long
applications in C also.

On the other hand, I don't want to place arbitrary restrictions on long scripts
just because I'm mean and nasty.

Larry Wall
lwall@jpl-devvax.Jpl.Nasa.Gov