The Surprisingly Tense History of the Schwartzian Transform

Alpine Perl Workshop 2016 • brian d foy

The Surprisingly Tense History of the

Schwartzian Transform

The Perl Review • www.theperlreview.com

http://bit.ly/2bHNNx4

Randal Schwartz

Just another

hacker.

• troff• emacs•Lisp•Perl•Smalltalk•…

Tom Christiansen

• Languages geek • Csh god• Perl evangelist

The Surprisingly Tense History of the Schwartzian Transform The Technique

Its ExpressionThe Arguments

Its NameThe Reckoning

decoratesort

undecorate

computeassociate

sortmap

Richard Stallman

• Editor editor• GNU• Free Software

TECO - Text Editor and CorrectorEmacs - Editing MACroS EINE - E. Is Not Emacs

ZWEI - Z. Was EINE InitiallyGNU Emacs

The Surprisingly Tense History of the Schwartzian Transform Lisp

(defun schwartzian-transform (list costly-function predicate) (mapcar #'cdr

(stable-sort (mapcar (lambda (x) (cons (funcall costly-function x) x))

list) predicate :key #'car)))

(require :sb-posix)(schwartzian-transform (directory "/etc/*") (lambda (x) (sb-posix:stat-mtime (sb-posix:stat x))) #'<=)

http://codereview.stackexchange.com/a/138436/13050

The Surprisingly Tense History of the Schwartzian Transform December 16, 1994

#!/usr/bin/perlrequire 5; # new features, new bugs!print

map { $_->[0] }sort { $a->[1] cmp $b->[1] }map { [$_, /(\S+)$/] }<>;

Randal Schwartz in comp.unix.shells

The Surprisingly Tense History of the Schwartzian Transform Unfamiliar

ComplexUndocumentedHard to learn

Too cleverNew

Different

The Surprisingly Tense History of the Schwartzian Transform OMFG

AwesomeNew featuresLists of listsPower tools

Not documented

Easy to learn

Power tools

The Surprisingly Tense History of the Schwartzian Transform FMTEYEWTK

I'm not ragging on Randal, merely teasing a bit. He's just trying to be clever, and that's what he does. I'm just submitting a sample chapter for his perusal for inclusion the mythical Alpaca Book :-)

Tom Christiansen

Far More Than Everything You've Ever Wanted to Know About Sorting, http://www.perl.com/doc/FMTEYEWTK/sort.html

The Surprisingly Tense History of the Schwartzian Transform August 30, 1995

Or for possibly more efficiency, ensure that the calls only happen once per record, rather than approximately NlogN times, with the Schwartztransformation:-)

@keys = map { $_->[0] }sort { $a->[1] <=> $b->[1] or $a cmp $b }map { [ $_, datexform($foo{$_}) ] } keys %foo;

Bennett Todd in comp.lang.perl.misc

https://groups.google.com/forum/?hl=en#!topic/comp.lang.perl.misc/fLo0RNV8oW8

The Surprisingly Tense History of the Schwartzian Transform January 1996

http://www.stonehenge.com/merlyn/UnixReview/col06.html

Randal explains map-sort-map in Unix ReviewI'm going to talk about some sorts of sorts, and hopefully you'll sort everything out by the time you're finished reading. (And no, despite the similarity to my name, I will not talk about ``random sorts''.)

The Surprisingly Tense History of the Schwartzian Transform April 1996

Tom labels a benchmark "Schwartzian XFrom" in comp.lang.perl.misc for “Read directory in timestamp order?”

https://groups.google.com/d/msg/comp.lang.perl.misc/pw-Hl4byLnc/yzejRnku3RoJ

The Surprisingly Tense History of the Schwartzian Transform July 1996

https://groups.google.com/d/msg/comp.lang.perl.misc/6NEeX4XJx54/nmpMmReMIbcJ

Colin Howarth in comp.lang.perl.misc

"Schwartzian transform of %$self ... help?"

The Surprisingly Tense History of the Schwartzian Transform October 1996

Tom posts a draft of perllol with "Schwartzian Transform"

The Surprisingly Tense History of the Schwartzian Transform December 1996

https://groups.google.com/d/msg/comp.lang.perl.misc/fPx42DB2jd8/cC_6osV70mMJ

Tom in comp.lang.perl.misc

I'm still pissed at Randal for having posted it, especially the way he did.

I hereby propose that the aforementioned Lispism, yclept “Schwartzian Transform", be recast in a less Teutonic albeit darker light; to wit, "Black Transform", as this spelling more accurately connotes its sinister subtleties. :-)

Tom later in the same thread

The Surprisingly Tense History of the Schwartzian Transform December 1996

I wonder if this chunk of code will haunt us forever.

Eric Arnold in comp.lang.perl.misc

https://groups.google.com/d/msg/comp.lang.perl.misc/fPx42DB2jd8/CTRmyWyJW6MJ

The Surprisingly Tense History of the Schwartzian Transform 1999

The Surprisingly Tense History of the Schwartzian Transform Orcish Manuever

@sorted = sort {( $times{$a} ||= -M $a ) <=>( $times{$b} ||= -M $b )

} @old_array;

Perl 4 compatible version

The Surprisingly Tense History of the Schwartzian Transform 2000

The Surprisingly Tense History of the Schwartzian Transform Python 2.4, 3

sorted = sorted(string_list, key=…)

string_list.sort(key=lambda …)

map(lambda x: x[1], sorted( map(lambda x: (f(x), x), old_list)))

new_list = zip(* sorted( zip(map(f, old_list), old_list)))[1]

The Surprisingly Tense History of the Schwartzian Transform Python 2

tmp2 = [ (int(s[10:15]), s) for s in L ] tmp2.sort()Isorted = [ x[1] for x in tmp2 ]

sorted([5, 2, 4, 1, 3], cmp=…)

The Surprisingly Tense History of the Schwartzian Transform Ruby

[1,1.1,1.2,10].sort_by {|n| n.to_s}

•Innsbruck - CC BY 2.0 by Reisender1701 (Flickr) https://goo.gl/PuILnA

•Randal Schwartz - CC BY-SA 3.0 by Chris Marquardt https://commons.wikimedia.org/wiki/File:Randal_Schwartz_headshot_by_Chris_Marquardt.png

•Tom Christiansen - CC BY-SA 3.0 by Tim Bray https://en.wikipedia.org/wiki/File:Tom_Christiansen_in_2008.jpg

•Richard Stallman - CC BY-SA 3.0 by Thesupermat https://commons.wikimedia.org/wiki/File:Richard_Stallman_-_Fête_de_l%27Humanité_2014_-_010.jpg

The Surprisingly Tense History of the Schwartzian Transform

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