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From: martin@kuling.UUCP (Erik Martin)
Newsgroups: net.ai,net.lang.lisp
Subject: Re: Common LISP style standards.
Message-ID: <945@kuling.UUCP>
Date: Sat, 17-May-86 20:52:32 EDT
Article-I.D.: kuling.945
Posted: Sat May 17 20:52:32 1986
Date-Received: Sat, 24-May-86 00:07:45 EDT
References: <2784@jhunix.UUCP>
Reply-To: martin@kuling.UUCP (Per-Erik Martin)
Distribution: net
Organization: The Royal Inst. of Techn., Stockholm
Lines: 63
Xref: linus net.ai:3240 net.lang.lisp:745

In article <2784@jhunix.UUCP> ins_amrh@jhunix.UUCP writes:
>
>	- How do you keep track of the side effects of destructive functions
>	  such as sort, nconc, replaca, mapcan, delete-if, etc?
Don't use them. I use destruction only when I need circular objects or
when I need to speed up a program. In the latter case I write it strictly
functional first and then substitute 'remove' with 'delete' and so on. This
should not affect the semantics of the program if it is 'correctly' written 
from the beginning. But it's really a task for the compiler so You shouldn't
need to think about it.

>	- When should you use macros vs. functions?
I only use macros when i need a new syntax or a 'unusuall' evaluation
of the arguments. (like FEXPR in Franz and MacLisp.)

>	- How do you reference global variables?  Usually you enclose it
>	  in "*"s, but how do you differentiate between your own vars and
>	  Common LISP vars such as *standard-input*, *print-level*, etc?
Allways "*"s. No differentiation.

>	- Documentation ideas?
An 'owerview' description in the file header, more detailed on top of each
function. Very few comments inline, use long function and variable names
instead. Documentation strings in global variables and top level (user)
functions.

>	- When to use DOLIST vs MAPCAR?
Quite obvious. Use DOLIST when you want to scan through a list, i.e. just 
look at it. At the end of the list it returns NIL or the optional return form.
You can also return something with en explicit RETURN. Use MAPCAR when you
want to build a *new* list with a function applied to each element.

>	- DO vs LOOP?
Write what you mean. If you mean 'repeat until dooms day' (whithout any
variables bound) then use LOOP. 

>	- Indentation/format ideas?  Or do you always write it like the
>	  pretty-printer would print it?
A lot of white space in the code. The rest is very personal and hard to set
up rules for. Nice editors usually have good ideas about how it should look
like.

>	- NULL vs ENDP, FIRST vs CAR, etc.  Some would say "FIRST" is
>	  more mnemonic, but does that mean you need to use
>	  (first (rest (first X))) instead of (cadar X) ??
Again, write what you mean. If you mean 'is this the end of the list
we are just working with?' then use ENDP, if you mean 'is this NIL (an empty
list)?', use NULL, and if you mean 'is this false?' use NOT.
Write FIRST if you mean the first element of a list, SECOND for the second,
THIRD for the third...and compinations of these when appropriate. At some 
limit this gets very messy though, and C*R is better. But in that case you
perhaps should write your own accessor functions. When working with cons'es 
I always use CAR and CDR.


My general rule is : Write what you mean and leave the task of efficiency
to the implementation and compiler.


					Per-Erik Martin
-- 
Per-Erik Martin,  Uppsala University, Sweden
UUCP: martin@kuling.UUCP  (...!{seismo,mcvax}!enea!kuling!martin)