Re: syntax question for defun

[<tomas@tuxteam.de>]

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On Wed, Aug 28, 2024 at 01:01:33PM -0700, David Elson wrote:
> Hello. I have been using emacs for ... a while.
> 
> For questions, I have often browsed and browsed (i.e. googled) and ... and
> usually find a good explanation. But sometimes I don't find an answer, even
> when it is staring right at me.
> 
> My question:
> 
> To emulate something akin to the PL1/C/C++ arrow notation, I have used:
> 
> *(defun -> (object method &rest args) ...)*
> 
> and it works.
> 
> *Is this valid elisp/lisp?*

It is. From the elisp documentation:
 -- Macro: defun name args [doc] [declare] [interactive] body...
     ‘defun’ is the usual way to define new Lisp functions.  It defines
     the symbol NAME as a function with argument list ARGS ...

... so NAME is a symbol. Again, from the doc:

   A symbol name can contain any characters whatever.  Most symbol names
  are written with letters, digits, and the punctuation characters
  ‘-+=*/’.  Such names require no special punctuation; the characters of
  the name suffice as long as the name does not look like a number.  (If
  it does, write a ‘\’ at the beginning of the name to force
  interpretation as a symbol.)  The characters ‘_~!@$%^&:<>{}?’ are less
  often used but also require no special punctuation.  Any other
  characters may be included in a symbol’s name by escaping them with a
  backslash.

So "->" is not only a legal symbol name, but also one that doesn't need
special escaping to be seen as such. So go wild :)

Actually, Emacs Lisp comes with one function named "-" and another named
">".

That said, this doesn't mean that other people will find your code readable
or enjoyable. It's on you to find that out :-)

> If it works only coincidentally, then it might break in the future, when a
> pressing emacs issue is resolved in a manner that requires plugging this
> "loophole".
> 
> If it is formally valid, where does it document the level of flexibility
> that allows this syntax?

The Emacs Lisp documentation should be your go-to place for such questions.

Cheers
-- 
t

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