Re: When do you re-export?

[Wojtek Kosior via <help-guix@gnu.org>]

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> Hi,
> 
> When should I re-export something in a module?
> 
> docs say [...]
>
> The docs don't explain why you would want to even do a re-export in the first place...
> 
> Could someone provide some examples as to why I would want to use this? It
> would be much appreciated!
> 
> --
> jgart

Hello,

Although I have very little scheme knowledge (disclaimer) I thought I
could perhaps help using some generic programming knowledge.

It seems re-exporting things is just helpful for maintaining the
desired code structure. If you're for example writing a library, you
might find it useful to split the code into several modules.

Typically, only a subset of the functions and structures you define are
meant to be exported as library's external API. Meanwhile, as a result
of various dependencies between them, the definitions you want to make
public might have landed in different code files and effectively in
different modules. Now, in order to make them available to library
users by the means of a single import, it is perfectly justifiable to
have them imported by and re-exported by a single module.

Guix itself seems to be doing something like that[1].

And making a "re-export all public definitions" wrapper is just an
example. There may be other reasons we might want to have 'foo'
importable from module 'bar' despite it being originally defined in
some other module (e.g. 'baz') ☺

Best,
Wojtek

[1] https://git.savannah.gnu.org/cgit/guix.git/tree/guix.scm#n23


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On Tue, 11 Oct 2022 16:28:48 -0500
jgart <jgart@dismail.de> wrote:

> Hi,
> 
> When should I re-export something in a module?
> 
> docs say the following:
> 
> Add all variables (which must be symbols or pairs of symbols) to the
> list of re-exported bindings of the current module. Pairs of symbols
> are handled as in export. Re-exported bindings must be imported by the
> current module from some other module.
> 
> The docs don't explain why you would want to even do a re-export in the first place...
> 
> Could someone provide some examples as to why I would want to use this? It
> would be much appreciated!
> 
> --
> jgart
> 



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