Paul Rubin wrote:
> Ken Tilton <[EMAIL PROTECTED]> writes:
>
>>>Man that whole thing is messy. I can't for the life of me understand
>>>why it's so important to use a macro for that. Even in Lisp, I'd
>>>probably set up the reverse thingie as an auxiliary function.
>>
>>And when you got to skill 42 and you discovered you needed a new
>>optional argument to the reversal method you would throw up your hands
>>and register for bartending school rather than go edit the other 41.
>
>
> I don't see the problem. Python uses keyword args sort of like
> Lisp's, and the called function (if it asks) receives a dictionary
> containing any keyword args not bound explicitly in the arg list.
> So you can invent new args whenever you want.
I am not making this up. I just decided to change the signature to the
reversal function(s). I had been clever, trying to pass in just what I
deemed necessary from a transformation (TF) data structure that needed
reversing, now I recall -- because I needed something else from the TF
-- I should never try to be smart, just pass in the whole frickin TF (duh).
So this:
(defmethod tf-reverse (id (eql ',sub-id)) resx (drv-opnds tf drv))
,@reverser)
becomes this:
(defmethod tf-reverse ((id (eql ',sub-id)) tf drv
&aux (opnds (drv-opnds tf drv)))
(loop for resx in (results drv)
,@reverser))
I pass in drv (a derivation, a part of a transformation) because (I
forgot) reversal code has to reverse each derivation of a TF separately.
In the new macroexpansion I preserve the bindings RESX and OPNDS
expected by the 41 (not really, but it could be) existing uses of the
defskill macro, and then <gasp> move an iteration across possible
multiple results (RESXs) of a TF into the generate tf-reverse method
(and the poor body of code has no idea I did that).
At this point if I had to redo these manually we can forget bartending
school, I'd be going straight to the Betty Ford clinic .
btw, you called the defskill messy (repeated below) "messy". The only
text not specific to absolute value is D-E-F-S-K-I-L-L. Expanding that
into "tidy" separate methods adds 25% of dead weight boilerplate. In 4-5
separate toplevel definitions instead of one. How is that less messy?
ken
(defskill absolute-value
(title "Absolute Value")
(annotations
"Take the absolute value of #signed-value#."
"The vertical bars around #signed-value# mean 'the absolute value
of' #signed-value#."
"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 #signed-value# 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
#signed-value#?"
"Some examples: #str|+42|=42#, #str|-42|=42#, and #str|0|=0#."
"To get the absolute value of a number such as #signed-value#, we
simply drop any minus sign.")
(reverse
(ensure-cloning resx
(make-instance 'mx-number
:value (loop with op1 = (car opnds)
with log = (max 1 (ceiling (log (abs (value op1)) 10)))
for n = (* (signum (value op1))
(+ 2 (random (expt 10 log))))
when (/= n (value op1))
return n)
:representation (representation resx)))))
--
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
--
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