setf v defparameter

[Old-RPGer]

Page 27 introduced setf (smaller) & (bigger). Page 28 (start-over)
reverts to defparameter. What's the virtue of using setf v
defparameter?

[Conrad]

Hi Old-RPGer:

Actually, defparameter is introduced on page 22. You use defparameter
to define new "global" variables (can also be done with defvar) and
use setf to set existing variables.

There's a lot of history as to why these two operations are treated
separately in Common Lisp. The basic gist of it is that it's useful to
know if you're accidentally redefining variables. See the discussions
of defvar and "generic setters" in the book for more detail (though my
book doesn't cover 100% of the esoteric details of this issue.)

[Dan Brooking]

So basically there would not be anything wrong semantically with using defparameter instead of setf?  It's just a design choice to use setf to explicitly state what your intentions are with the command?

[Purity Control]

HI Dan,

These two links should give you all the juicy details.

http://www.lispworks.com/documentation/HyperSpec/Body/m_defpar.htm

http://www.lispworks.com/documentation/HyperSpec/Body/m_setf_.htm

That will explain the semantic issues for you. 

What I would say though is that the vast majority of code is written seldom and read lots so intentions mean a lot. Its nice to be kind to anyone who may have to read your code (including yourself). :-)

Hope that helps.