Re: Backquotes and commas and ",@"

[Steinar Bang <sb@dod.no>]

>>>>> Andreas Schwab <schwab@linux-m68k.org>:
> Steinar Bang <sb@dod.no> writes:

>> This means that the gnus-sync-lesync-pre-save-group-entry function
>> returns a list.

> More specifically, it returns an alist of key/value pairs.

Right!  That makes sense.

>> - Then the list will have an element that is a two element list,

> It's a cons whose car is the key and cdr is the value.

Right!  And a cons cell isn't a two element list.  A two element list
would have been two cons cells, with the car of each cell holding the
elements.

>> consisting of the symbol '_id and the first element of the nentry
>> argument to the function (I don't understand why you have to have
>> the "." there, though...?)

> Because you want the cdr to be the value of the key, not the cadr.

And refreshing my lisp knowledge:
 - cdr is the second slot of a cons cell, ie. the one pointing to the
   next cons cell of the list
 - cadr is the car of the cdr ie. (cadr '(1 2)) is 2.  However '(1 2)
   creates a two element list (ie. two cons cells with the car of the
   first cons cell being 1 and the car of the second cons cell being 2).
   And indeed (cadr (1 . 2)) fails (as one would expect from cadr's
   definition

Ah... "value of the key" is somewhat ambigous.  I took that to mean,
well... the value of the key.  While you meant the value that can be
looked up, using the key, and in which case your sentence makes sense.

So... I looked up the definition of alist, and it's indeed a list of
cons cells (which isn't surprising when one stops to think about it).

> Splicing the empty list will splice nothing.

I suspected that this might be the case, but didn't stop to look it up.