On Fri, Mar 31, 2017 at 07:56:18PM -0400, Kei Kebreau wrote:
> The surrounding code definitely seems to suggest that. Reading "up" the
> code from the gexp->derivation call I can find hardcoded xz usage in the
> tarxz-name procedure and this bit:
> 
> (mlet %store-monad ((tar ->     (lookup-input "tar"))
>                   ->(xz ->      (lookup-input "xz"))
>   (only xz here!)/  (patch ->   (lookup-input "patch"))
>                     (locales -> (lookup-input "locales"))
>                     (decomp ->  (lookup-input decompression-type))
>                     (patches    (sequence %store-monad
>                                           (map instantiate-patch patches))))

Right, that's what I was looking at.