Author Archives: bhyde

tidy up the output of lisp macros

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For some reason it makes my teeth hurt to have my macros generate code that I wouldn’t have written by hand.  For example it’s not hard to get code like this out of a macro expansion.

(let ()
  (progn
    (if (fp x)
      (progn 
         (f1 x)
         (f2 x)))))

v.s. what I might like:

(when (fp x)
   (f1 x)
   (f2 x))

I probably ought to just relax and ignore it, but instead I often revise macros so the code they generate is nicer to look at.   So that:

`(let ,vars ,@body)

becomes

(if vars
    `(let ,vars ,@body)
    `(progn ,@body))

This is silly!   Now I have ugly macros instead of ugly output.   I’m just moving the ugly bits around.

So I’ve started doing this:

(tidy-expression `(let ,vars ,@body))

where tidy-expression is something like this:

(defun tidy-expression (x)
  (match x
    (`(or ,a (or ,@b)) `(or ,a ,@b))
    (`(progn ,a (progn ,@b)) `(progn ,a ,@b))
    (`(progn ,x) x)
    (`(and ,a (and ,@b)) `(and ,a ,@b))
    (`(if ,a (progn ,@b)) `(when ,a ,@b))
    (`(if ,a (progn ,@b) (progn ,@c)) `(cond (,a ,@b) (t ,@c)))
    (`(if ,a (progn ,@b) ,c) `(cond (,a ,@b) (t ,c)))
    (`(if ,a ,b (progn ,@c)) `(cond (,a ,b) (t ,@c)))
    (`(let ,vs (progn ,@body)) (tidy-expression `(let ,vs ,@body)))
    (`(let nil ,@body) (tidy-expression `(progn ,@body)))
    (_ x)))

It’s another chapter in my crush on optima.

I write these tidy up functions as necessary.

That example only chews on the top of the form.   If you wanted something to clean up the first example you’d need to write tidy-expression-all.

(tidy-expression-all
 '(progn
   (if (fp x)
       (progn 
         (f1 x)
         (f2 x)))))
-->
(when (fp x) (f1 x) (f2 x))

This all reminds me of Warren Teitelman’s programmer’s assistant in Interlisp.  It reminds me of some of the things that flycheck in Emacs does for other programming languages.   It reminds me that I’ve been wondering what would a lint for Common Lisp would look like.

I bet somebody already wrote a generalized tidy expression and I just don’t know were to look.

Inviting Disaster

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James Chiles’ “Inviting Disaster: Lessons from the Edge of Technology” is a fun read, except that it’s a spoiler for the books that tells the story of just one of these disasters.  The best part of the book, and the part you never get in books like this and certainly not in the books about a single debacle, is a section where he tells a few stories about people doing the right things to avoid the horrible outcome.

I particularly liked learning that Nobel had so much trouble getting with workers smuggling matches into the factory that finally he started making them strip naked each morning and walk thru a pool up to their neck.

It disappoints in some ways: there are no financial disasters and no software disasters.  There are no examples of failures of collective action or public good management, i.e. levee failures.  Or for that matter catastrophes caused by a the false sense of security that comes from gradual processes.

Since it’s mostly stories it is not a very useful book if you want to learn what makes dangerous systems and what to do about it.  Normal Accidents remains a good starting point for that.  But stories are fun, and very useful.  Everybody ought to read a few of the books on this shelf in the Library.

Oh, and don’t try to extinguish a fire by flooding the cargo hold with steam when it’s loaded with fertilizer.

Lint for your shell scripts!

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ShellCheck will critique your shell scripts, i.e. it’s a static checker for Bash etc.  You can try it online at shellcheck.net.  You can also install it on your own machines.

If you combine it with emac’s flycheck it is particularly delightful!

I had trouble installing it locally.  I believe this recipe works.  It’s written in Haskell, so first your install Haskell’s package manager cabal.  I used brew cabal-install.  Then do cabal update.  At that point you clone shellcheck from github (git clone https://github.com/koalaman/shellcheck.git) and cd into the resulting directory cd shellcheck and run cabal install. Sometime later ~/.cabal/bin/shellcheck appears, and you can set flycheck-sh-shellcheck-executable so flycheck can find it.

Wolfram Alpha

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Watching these into to Wolfram Alpha videos (for example) give me a certain arousal that I have experienced only a handful of times.  The first time was when I discovered the APL prompt hidden inside the Dartmouth Basic CLI on the Teletype in high school.  Then there was Focal on the PDP-12 which let you draw charts on the machine’s CRT.  Latter there was discovering that I could run Mathematica at MIT over the Arpanet from CMU.  And, of course, the Lisp Machine.  I don’t know what it is about these systems that gets me excited.  R, Prolog, Erlang, Emacs all got close but never managed to trigger this curious arousal for me.

Wolfram Alpha is a lovely example of what is now possible.  The Lisp Machine was so very similar, particularly with its UI, to what that demos is showing.  But what’s new is the amount of data and algorithms we can now bring to bear.  Where are the engineering stations that treat the entire web’s as a reasonably well-organized dataset?  That is/was the RDF fantasy.  It’s nice to see it starting to pop-up up.

Of course it’s unlikely that I’d invest a lot in climbing the learning curve of a system like this, given that it’s proprietary.

Update: Article in Slate, and a classic on Wolfram’s ego and many other flaws.

,@ v.s. ,.

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I’m surprised that I didn’t know about the ,. construct in Common Lisp’s backquote syntax.  It is equivalent to ,@ except that it licenses the implementation to destructively modified the tail of the list being inlined.

cl-user> (defparameter *x* '(1 2 3))
*x*
cl-user> *x*
(1 2 3)
cl-user> `(a b ,@*x* c d)
(a b 1 2 3 c d)
cl-user> *x*
(1 2 3)
cl-user> `(a b ,.*x* c d)
(a b 1 2 3 c d)
cl-user> *x*
(1 2 3 c d)
cl-user>

Think Fast

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I enjoyed watching this interview (~ a hour) with Daniel Kahneman.  His book, “Thinking, Fast and Slow” is delightful and very meaty.  Obviously it’s organizing principle is to partition the way we make decisions into the two classes mentioned in the title.

The interview suffers a bit because they keep insisting on using the term heuristic (as in short cut for figuring something out) to describe both kinds of thinking.

For example say we are asked how much something is worth.  We might quickly recall some number mentioned recently and interpolate an answer from that number – this trick is sometimes called anchoring.  Or we might query Amazon and use that number.  Both are heuristics but the first is often described as a near instantaneous scheme that people use, so quick that they are largely unaware of it.

At first I was confused by the discussion since the list of fast heuristics was short.  I have a long list.  Accumulated over the years, of fast thinking tricks people use.  For example there is consistency: i.e. when faced with a choice we will default to taking the same choice as last time.  I have a list is because so much of popular psychology (and marketing) involves tricking people into making mistakes based on one of these.  You can then making fun of (or profit off) them.

But in pretty quickly it becomes clear that Kahneman’s view is more nuanced than that.

The fun thing he says about that list is that he has grown affectionate for a universal rule of fast thinking, i.e. that when faced with any puzzle we seek to reframe it, very fast, into another puzzle that we already have solved.

Frame that as advice:  Don’t try to answer the question, instead answer a different nearby question.  One your familiar with.

This lazy problem solving heuristics works fine both fast and slow.  You can engage in satisficing slowly, savoring the process.  Go ahead, spin up a long story based on evolution, free markets, the history of the last century, or what ever your into.   Nothing obviously wrong with that.  It is often fun, entertaining, and interesting.  Sadly it’s often lazy too.

Cost of Cars

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This chart shows the Urban Consumer Price Index for cars divided by the total CPI since 1980.  Thirty years of falling car prices ended with the great recession.  Fire up your insta-theories(tm).

 

Update: I think I understand this now.  Growth in the medical sector dominates the total CPI.   If you divide any other segment of the CPI by the total CPI you will get a chart that’s similar to this one, i.e. one that shows that below trend growth for that segment.  Nothing can compete with medical for such growth.

 

Deceptive Status Signals

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This essay on deceptive status signals (aka DSS) is delightful for the
collection of tricks people use to look higher status than they really
are.

  • Pulled over for using a cell phone, but it turns out to be a toy.
  • Filling your grocery cart with high-priced goods, and then abandoning it.
  • Driving with the windows closed, signalling that you have air condition.
  • Shirts with no backs.
  • Expired credit cards
  • Packaging for luxury goods
  • Carrying Fast Food packaging
  • Wearing just the cap of a pen in your pocket
  • TV antenna, but no TV
  • Using infant formula
  • Houses with brick fronts, but otherwise made of mud.

If your into it the jargon in this essay is fun. “A related
DSS strategy is the display of a cheap item that is complementary to a
prestigious consumer good.” helps explains the TV antenna, luxury good packaging, …

So, I wonder: could I hack the stream of Ads
appearing in my browser to create a deceptive status signal.

Social Marketing: Shame & Peer pressure edition

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I think the first time I noticed social  marketing was a few decades ago when a phone company started offering friends and family discount plans.  These, from the point of view of the firm, were clever because the locked the customer into a plan, since switching would need explaining to your friends and family why you were abandoning them.

Another famed example of social marketing was the viral marketing used by Hotmail.  Customer emails were infected with advertising in the hope that their correspondents would thing the customer was providing a product endorsement.

So here’s a new one.  Verison’s Fios division has an Ad running with the tag line “Is it you?”.  Pairs of customers ask this of each other with the implication that one of them is failing to provide a high quality relationship because she hasn’t signed up for Fios.  Shame on her!

Immersion Cooling

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I fell into one of those Internet rabbit holes.  Immersion cooling for servers with liquid that boils in contact with the hot spots.  3M makes some materials used for fire suppression and cooling that are good for this.  Here is a DIY example with a board laid on the bottom of a fish tank.   Here’s is a forum posting about a bit coin miner that uses this technique.  This video gets into some of the details about how to get better boiling.  Lots of interesting heat transfer problems.  In time will change entirely how electronics is packaged.   For example I bet people are working on using this stuff in laptops.  That last one is from a guy at 3M who has a facebook page about their research.  Here’s a video where the actual chip is exposed and you can see the hot spots on the chip.  Searching on Google for immersion cooling videos will turn up more examples.

These systems use one of variants of 3M’s Novec.  It costs a few hundred dollars per gallon.