What does the argument list in C-h f delete-duplicates mean?

[Alan Mackenzie]

Hello, XEmacs.

When I do C-h f delete-duplicates, the resulting text starts off:

`delete-duplicates' is a built-in function
-- loaded from "/home/acm/emacs/xemacs.hg/xemacs/src/sequence.c"
(delete-duplicates SEQUENCE &key (TEST #'eql) (KEY #'identity) (START 0) END FROM-END TEST-NOT)

. What does this mean? In particular, I have never seen parenthesised
expressions, such as "(TEST #'eql)" inside an argument list before. The
XEmacs manual (page "Name Help") doesn't explain this. Are TEST, KEY
and START some sort of optional parameters, or what?

Thanks for the elucidation!

[Aidan Kehoe]

Hello Alan,

Post by Alan Mackenzie
`delete-duplicates' is a built-in function
-- loaded from "/home/acm/emacs/xemacs.hg/xemacs/src/sequence.c"
(delete-duplicates SEQUENCE &key (TEST #'eql) (KEY #'identity) (START 0) END FROM-END TEST-NOT)
. What does this mean? In particular, I have never seen parenthesised
expressions, such as "(TEST #'eql)" inside an argument list before. The
XEmacs manual (page "Name Help") doesn't explain this. Are TEST, KEY
and START some sort of optional parameters, or what?

Yes, they’re optional keyword parameters, as also used, for example, by
#'make-hash-table. The docstring for defun* goes into more detail on the
syntax.

I have been considering moving the extra functionality offered by defun* into
defun, but there are possible bootstrapping complications; if I do it I’ll
move the relevant documentation into the defun docstring, if I don’t I’ll add
a cross-reference to all the C functions that use keywords. Thanks for
pointing out the weakness in our docs!

Best,

Aidan

[Alan Mackenzie]

Hello, Aidan.

Post by Aidan Kehoe
Hello Alan,

Post by Alan Mackenzie
`delete-duplicates' is a built-in function
-- loaded from "/home/acm/emacs/xemacs.hg/xemacs/src/sequence.c"
(delete-duplicates SEQUENCE &key (TEST #'eql) (KEY #'identity) (START 0) END FROM-END TEST-NOT)
. What does this mean? In particular, I have never seen parenthesised
expressions, such as "(TEST #'eql)" inside an argument list before. The
XEmacs manual (page "Name Help") doesn't explain this. Are TEST, KEY
and START some sort of optional parameters, or what?

Yes, they’re optional keyword parameters, as also used, for example, by
#'make-hash-table. The docstring for defun* goes into more detail on the
syntax.

Thanks, that's helpful.

Post by Aidan Kehoe
I have been considering moving the extra functionality offered by defun* into
defun, but there are possible bootstrapping complications; if I do it I’ll
move the relevant documentation into the defun docstring, if I don’t I’ll add
a cross-reference to all the C functions that use keywords. Thanks for
pointing out the weakness in our docs!
Best,
Aidan