A SHORT BALLAD DEDICATED TO THE GROWTH OF PROGRAMS

[newdep]

...an old one...



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





    A SHORT BALLAD DEDICATED TO THE GROWTH OF PROGRAMS

    ==================================================

                      by

                  Ashwin Ram

   

    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))

   

                        :-)    

    ==================================================