> > Running `guix shell --pure ghc-esqueleto -D ghc-bytestring-builder`
> > results in an environment that has the base64-bytestring package (from
> > ghc-base64-bytestring) visible, even though it is not listed on listed
> > the command line (ghc-bytestring-builder doesn't dependend on it). It
> > seems to "leak" from the inputs of ghc-esqueleto which does depend on
> > ghc-base64-bytestring.
> 
> What do you mean by “leak”?

I would expect packages to keep their (non-propagated) inputs separate
from the environment I use. Here ghc-esqueleto makes it's haskell inputs
visible to the ghc in my environment.

> Does it happen if you run
> 
>     guix shell -C ghc-esqueleto -D ghc-bytestring-builder
> 
> ?

Yes it does.