merits of Lisp vs Python

[Ken Tilton]

Ken Tilton wrote:
> 
> 
> Paul Rubin wrote:
> 
>> Ken Tilton <kentilton at gmail.com> writes:
>>
>>> Have you read On Lisp by Paul Graham? It is on-line. Just the preface
>>> will do, I think, maybe also Chapter One where he raves on macros. Do
>>> you think he is mistaken? Confused? Lying? Mutant?
>>
>>
>>
>> I remember Paul Graham's piece about macros that made him sound like
>> someone who went nuts with them, as is certainly possible to do.
> 
> 
> But you could have just flipped thru the rest of the pages to see if he 
> /had/ gone nuts with them!
> 
>>  In
>> my experience, good coders write for clarity and that includes in
>> their use of Lisp macros.  All in all Lisp's macro system is something
>> like the C preprocessor.  Yes, you can obfuscate things horribly with
>> it, but you can also use it to make things clearer, and that's what
>> good programmers do.
> 
> 
> One has to be from the US and of a certain age to remember this, but 
> this old line from a commercial for high-octane gasoline says it for me: 
> power to be used, not abused.

Here is a bit of concrete I just tossed off:

(defmacro defskill (id &body skill-info)
   `(progn
      ,@(loop with sub-id = id
          for (q . q-def) in skill-info
          collecting
            (ecase q
               ((title annotations hints)
                `(defmethod ,(intern (conc$ 'skill- q)) ((tf-id (eql 
',sub-id)))
                      , at q-def))))))

It lets me code this:

(defskill absolute-value
     (title "Absolute Value")
   (annotations
    "Take the absolute value of #op#."
    "The vertical bars around #op# mean 'the absolute value of' #op#."
    "Absolute value of #strn# is the 'distance' of #strn# from zero."
    "Absolute value is always zero or positive: #str|n|=n#, and 
#str|-n|=n#.")
   (hints
    "What do those vertical bars around #op# mean?"
    "Have you learned about 'absolute value'?"
    "Absolute value can be thought of as the 'distance' of a value from 
zero on the number line, and distance is always positive."
    "The rule is:#str|-n|=|n|##str=n#.  Can you apply that to #op#?"
    "Some examples: #str|+42|=42#, #str|-42|=42#, and #str|0|=0#."
    "To get the absolute value of a number such as #op#, we simply drop 
any minus sign."))


...and get this:

(PROGN
  (DEFMETHOD SKILL-TITLE ((TF-ID (EQL 'ABSOLUTE-VALUE)))
     "Absolute Value")
  (DEFMETHOD SKILL-ANNOTATIONS ((TF-ID (EQL 'ABSOLUTE-VALUE)))
      "Take the absolute value of #op#." "The vertical bars around #op# 
mean 'the absolute value of' #op#."
      "Absolute value of #strn# is the 'distance' of #strn# from zero." 
"Absolute value is always zero or positive: #strn=n#, and #str-n=n#.")
   (DEFMETHOD SKILL-HINTS ((TF-ID (EQL 'ABSOLUTE-VALUE)))
      "What do those vertical bars around #op# mean?" "Have you learned 
about 'absolute value'?"
      "Absolute value can be thought of as the 'distance' of a value 
from zero on the number line, and distance is always positive."
      "The rule is:#str-n=n##str=n#.  Can you apply that to #op#?" "Some 
examples: #str+42=42#, #str-42=42#, and #str0=0#."
      "To get the absolute value of a number such as #op#, we simply 
drop any minus sign."))

The above is how my upcoming death-defying interactive Algebra 
tutor-in-a-drum ("You'll laugh! You'll cry!") will know how to coax some 
  befuddled teen through |-42| -> 42 if they get stuck. And a hundred 
other subskills (so there will be a hundred of these definitions).

If I hire someone they will look at defskill and not fall to the ground 
frothing at the mouth. They likely will not even macroexpand it because 
it is self-explanatory. If they wonder if there are other options they 
can alt-. to the source. The language has been extended, but I followed 
a pattern familiar to Lispniks. Zero confusion results.

If I decide not to use generic method dispatch to "look up" the hints I 
just have to change the macro and then write a DEFUN (no dispatch on 
type) to, say, look up the symbol in a hash table.

hth,ken

ps. I won't mention the other benefit, which is that I want educators to 
edit these if they have a better idea on how to tutor absolute value. I 
am not mentioning it because I am as impatient with superfluous syntax 
as a non-programmer would be. k

pps. How would Python do this? Is it possible to avoid committing to an 
implementation mechanism? Compare and contrast. k

-- 
Algebra: http://www.tilton-technology.com/LispNycAlgebra1.htm

"Well, I've wrestled with reality for thirty-five
years, Doctor, and I'm happy to state I finally
won out over it." -- Elwood P. Dowd

"I'll say I'm losing my grip, and it feels terrific."
    -- Smiling husband to scowling wife, New Yorker cartoon