#; as discard syntax instead of #_

[pyx]

I didn't know this feature as it's not mentioned in documentation until I saw #1636
It's hard to search on #_ so I bisected the repository and found out that it's been added quite a while 203965d, since last Aug.

But still, I suggest using #; as descard syntax instead of #_.

Rationale

• ; is the comment character (my wording maybe wrong) already
• #; is being used in scheme (SRFI-62), some implementations, Chichen, Guile
• free up _ (I know it can be shadowed, BTW) as user defined tag macro, in the case of i18n, function gettext is most likely imported as _, adding (_ ...) to every single string to existing code base is no fun, users can then define a tag macro, aptly named #_, as

(deftag _ [str]
  `(_ ~str))

;; using new import syntax #1614

(require .macro [_])
(import gettext [gettext :as _])

...

(defn run []
  (message-box #_ "hello world"))

and be done with it.

The cost of rename should be minimal, since it's not mentioned in documentation, I doubt many people using it currently, rename should not cause much trouble, while ; as tag macro is impossible to define by users, so nobody using it.

[pyx]

Edit: I was unaware of this section http://docs.hylang.org/en/stable/language/api.html#discard-prefix , it is documented already. I am sorry.

[refi64]

I think the idea behind using #_ is that it behaves less like a normal comment and more like a compile-time version of _ = xyz in that it discards something.

[pyx]

I sort of understand the reason _ being chosen in the first place, originated from a way to signify the value is of no importance, which in term, borrowed from ML languages.

In both python and strict MLs (OCaml for example), the expression being bound to _ is evaluated, then the result is discarded, while #_ as it is now, the next expression is discarded right away, not even being turned into AST, so I believe, in this regard, #; is actually telling what really happened behind the scenes.

[gilch]

#_ is the discard prefix used by Clojure and EDN, which is where we got the idea from in the first place. #; would have been a fair choice for Clojure, I suppose, but we've mostly been following Clojure's syntactic conventions, not Scheme's.

[refi64]

#; would also be harder for editors to highlight. Not too much more difficult, but a bit.

[pyx]

So this is an official "no", am I right?
If so, I will close this.

[gilch]

Well, officially, I think it takes three core members willing to revert a change for an absolute veto, but considering the lack of interest so far, the chances of this change getting approved don't look so good.

Clojure gives a stronger precedent for the current syntax, so I don't find the Scheme argument very convincing.

Currently _ is an alias for -, which is the shadow subtraction function, so you shouldn't import gettext by that name anyway. (We might change this #1635.) We also changed the repl history variables from _ to *1 *2 *3 like Clojure.

This does seem like a good use case for tag macros. But you still have a lot of options. I think __ would work, and #__ should work as a tag macro too. You could also just import gettext and do any number of other tags.

(import gettext[gettext])

 (deftag "18" [str]
  `(gettext ~str))

(defn run []
  (message-box #18"hello world"))

[pyx]

Thanks for the clarification. I might use #tr or #trs for gettext then, and #i18n for extra fun :). I will close this at the moment. In case someone else bring this up again, I will still be voting for #;