Cognitive Computing A research blog by Ashwin Ram, PhD

Date: 28 Jan 86 06:22:59 EST (Tue)
From: ram@yale-ring
Subject: Of growing code and diminishing hacks...
Sender: ram%yale-ring%arpa.yale@edu.mit.lcs.mc
To: t-discussion@arpa.yale, scheme@arpa.mit-mc

This is a tale of a sorry quest
To master pure code at the T guru’s behest
I enrolled in a class that appealing did seem
For it promised to teach fine things like T3 and Scheme

The first day went fine; we learned of cells
And symbols and lists and functions as well
Lisp I had mastered and excited was I
For to master T3 my hackstincts did cry

I sailed through the first week with no problems at all
And I even said “closure” instead of “function call”
Then said the master that ready were we
To start real hacking instead of simple theory

Will you, said he, write me a function please
That in lists would associate values with keys
I went home and turned on my trusty Apollo
And wrote a function whose definition follows:

    (cdr (assq key a-list))

A one-liner I thought, fool that I was
Just two simple calls without a COND clause
But when I tried this function to run
CDR didn’t think that NIL was much fun

So I tried again like the good King of yore
And of code I easily generated some more:

    (cond ((assq key a-list) => cdr))

It got longer but purer, and it wasn’t too bad
But then COND ran out and that was quite sad

Well, that isn’t hard to fix, I was told
Just write some more code, my son, be bold
Being young, not even a moment did I pause
I stifled my instincts and added a clause

    (cond ((assq key a-list) => cdr)
          (else nil))

Sometimes this worked and sometimes it broke
I debugged and prayed and even had a stroke
Many a guru tried valiantly to help
But undefined datums their efforts did squelch.

I returneth once more to the great sage of T
For no way out of the dilemma I could see
He said it was easy — more lines must I fill
with code, for FALSE was no longer NIL.

    (let ((val (assq key a-list)))
       (cond (val (cdr val))
             (else nil)))

You’d think by now I might be nearing the end
Of my ballad which seems bad things to portend
You’d think that we could all go home scot-free
But COND eschewed VAL; it wanted #T

So I went back to the master and appealed once again
I said, pardon me, but now I’m really insane
He said, no you’re not really going out of your head
Instead of just VAL, you must use NOT NULL instead

    (let ((val (assq key a-list)))
       (cond ((not (null? val)) (cdr val))
             (else nil)))

My song is over and I’m going home to bed
With this ineffable feeling that I’ve been misled
And just in case my point you have missed
Somehow I preferred (cdr (assq key a-list))

Here’s my latest geek poem: cognitivecomputing.wordpress.com/2010/10/11/a-is-for-apple—the-new-millennial-edition/