Your wai-extra was built using bytestring-0.9.2.1
, but you have a newer bytestring
package installed. Unless GHC is instructed to use the older version with a -package
flag or by hiding the newer, it picks the newest installed version of each package.
The package version is part of the types it defines, so the ByteString
of bytestring-0.9.2.1
is not the same type as the ByteString
of bytestring-0.10.0.0
(or whatever your newest version is).
You can
- compile the programme with a
-package bytestring-0.9.2.1
flag (but it could be that other used packages are built against a differentbytestring
version, then that wouldn't work). - build the programme as a
Cabal
ized package, thencabal-install
would figure out the necessary-package
flags and provide them to GHC (if it finds a consistent build plan). - rebuild
wai-extra
(and possibly a lot of other packages) against the newerbytestring
version. - unregister the newer
bytestring
version (which might require rebuilding some packages using the old version).