[Haskell-cafe] Proposal for an extension: in-module namespaces

Edward Z. Yang ezyang at mit.edu
Tue Mar 28 13:48:38 UTC 2017

There are a number of problems:

1. There is no support for mixed Backpack/regular module projects,
and it's not altogether clear how you would implement it, since it's
not obvious from file naming where a "module" might live.  This is
in contrast to something like anansi which generates hs files so that
the existing lookup codepaths work.

2. Recompilation avoidance operates on an entire bkp file, so if you
modify any submodule, you have to rebuild everything.  Not great if
you actually have a lot of code.

3. GHCi doesn't know how to deal with bkp files at all.

bkp files also support defining multiple libraries, which is a phase
violation with Cabal, and not really solvable at all.


Excerpts from Yuras Shumovich's message of 2017-03-28 16:43:54 +0300:
> 28-03-2017, Аўт а 09:22 -0400, Edward Z. Yang напісаў:
> > Excerpts from Yuras Shumovich's message of 2017-03-28 12:23:36 +0300:
> > > Also, I think backpack has some limited support for multiple
> > > modules in one
> > > file. At least I saw something similar in backpack examples in
> > > Edward
> > > Yang's blog.
> > 
> > You can put multiple modules in a bkp file, but that is mostly a tool
> > for compiler tests, and not intended to be used for "real" software.
> Thank you for clarification. Yeah, I think I saw it on GHC Trac too. It
> is very neat! But what prevents it from being useful for real software?
>  I often use anansi ( http://hackage.haskell.org/package/anansi ) when
> prototyping new projects, so that I can write multiple modules in one
> file. (One .anansi file generates a number of .hs files.) But it is an
> ugly workaround at best.
> Yuras.
> > 
> > Edward

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