[REBOL] Re: footer on Joel's email
From: joel:neely:fedex at: 18-Mar-2002 8:05
Hi, Charles,
OK, here are my deep dark secrets...
Charles wrote:
> Oh. The mystery commented portion is Perl... that makes sense,
> now. Hmm...
>
The point of the sig is to allow someone to discover my email
address without placing it in clear text, thus making it just
a little harder for spamvultures to harvest it from the plain
text of the email message. The email address (string) is
reversed, with the . and @ replaced with other characters.
That way a spamvulturebot that is looking for strings that
contain dots and at-signs would not pick up that line as an
encoded email address.
Here's an explanation of the sig, line by line:
; sub REBOL {}; sub head ($) {@_[0]}
Semicolon is the REBOL comment prefix (thru end of line);
this line contains Perl code to define:
- a null function named REBOL (to ignore the header);
- a function named "head" that returns its argument (this
will be explained below).
Since the REBOL interpreter is supposed to ignore everything
above the header I didn't actually need the semicolon. I left
it there as a hint, since I *do* need comment-escaped code
later on. An experienced REBOL programmer would know that it
wasn't needed, so that would draw attention to the question,
"Why did he make that a comment?" and provide a clue about the
use of language-specific commenting.
REBOL []
The REBOL header, to engage the REBOL interpreter. I needed
the null function "REBOL" in Perl to make this line legal in
both languages. The argument is an empty block to REBOL, but
is an anonymous array reference to Perl (which will silently
ignore it, due to the definition of the null function).
# despam: func [e] [replace replace/all e ":" "." "#" "@"]
This one is a tad obscure! ;-) I need functions to fix the
./: and @/# substitutions in both languages. Each of these
functions needs to be hidden from the other language (in the
simplest/shortest way possible). The octothorp/hash/pound
is the single-line comment prefix in Perl, just as ; is to
REBOL, *but* in REBOL it marks the beginning of an ISSUE!
data value (in this case, a zero-length one! ;-)
>> print #1234
1234
>> print #
>> type? #
== issue!
>> length? #
== 0
REBOL silently ignores expressions or simple values which
appear "between expressions" (i.e., without being used to
set a word's value, as function arguments, etc...) as long
as they have no side-effects. Thus I can begin the line
with a comment marker to make Perl ignore this line, but
it looks to REBOL like an extra trivial value that can be
ignored.
The rest of the line simply defines the DESPAM function to
REBOL as handling the punctuation (de)substitution.
; sub despam {my ($e) = @_; $e =~ tr/:#/.@/; return "\n$e"}
This is the Perlish version of the previous line. The
semicolon hides this line from REBOL. Semicolons are
used in Perl to separate statements/expressions, so this
just looks to Perl like an empty expression followed by
a function definition. There's one additional trick in
this function; the REBOL native PRINT puts a newline at
the end of what's displayed to the console. Perl doesn't
do that; it let's the script decide when/where to put in
line breaks. Therefore, the Perl "despam" function has
to put a newline at the *beginning* of its result (since
the result will be reversed before printing ;-).
print head reverse despam "moc:xedef#yleen:leoj" ;
Now I have all the functions I need in both Perl and REBOL;
both languages have "print" and "reverse" functions, and I've
defined "head" for Perl. The gimmick is that REBOL returns
a reversed series at its tail, but Perl returns a reversed
string at its beginning. Therefore I needed "head" for
REBOL, but the Perl version didn't need to do anything.
Lots of work for a five-line sig, but it was fun to get all of
the puzzle pieces lined up just right...
-jn-
--
; Joel Neely joeldotneelyatfedexdotcom
REBOL [] do [ do func [s] [ foreach [a b] s [prin b] ] sort/skip
do function [s] [t] [ t: "" foreach [a b] s [repend t [b a]] t ] {
| e s m!zauafBpcvekexEohthjJakwLrngohOqrlryRnsctdtiub} 2 ]
