Question on mandatory arguments for -> and ->> macros

[Shantanu Kumar]

Hi,

I am curious about the rationale for the mandatory arguments for ->
and ->> macros.

user=> (doc ->)
-------------------------
clojure.core/->
([x] [x form] [x form & more])

user=> (doc ->>)
-------------------------
clojure.core/->>
([x form] [x form & more])

For -> a form is optional, but for ->> it is not. Can anybody help me
understand why is there a difference?

Shantanu

[Stuart Sierra]

From the look of the source, there's no reason why ->> couldn't have arity-1. I guess it just doesn't come up much.

-S

[Shantanu Kumar]

On Monday, 8 October 2012 04:57:06 UTC+5:30, Stuart Sierra wrote:

From the look of the source, there's no reason why ->> couldn't have arity-1. I guess it just doesn't come up much.

Arity-1 for ->> would be useful to let somebody comment out forms as follows:

(->> foo

  #_(bar baz)

  #_quux)

I can file an issue on JIRA if this makes sense.

Shantanu

[Jason Wolfe]

+1 I've hit this issue before when generating a macroexpansion with ->> in it.  

Also, I think at some point -> and ->> weren't themselves properly namespaced in their own macroexpansions, not sure if it's still an issue but maybe worth checking while you're in there. 

Shantanu

[Shantanu Kumar]

Jason, do you have a snippet to reproduce the error you described?

Shantanu

[Jason Wolfe]

Now that I think about it, I believe the namespace issue was in -?> and -?>> from an old contrib library.  Sorry for the noise.

 

Shantanu

[Laurent PETIT]

2012/10/12 Jason Wolfe <ja...@w01fe.com>

Yeah, and I'm not sure it has been corrected yet, btw ?
 

 

Shantanu

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[Shantanu Kumar]

I have filed it as `enhancement` here: http://dev.clojure.org/jira/browse/CLJ-1086

Shantanu

[Stuart Sierra]

Thank you, especially thanks for tagging it an enhancement.
-S