Why are you trying to use join?  It's not a string function; it's a function on lists which accidentally does something useful on normal Strings because they're implemented as lists.  ByteStrings aren't lists, so there is no useful join, and ghc finds an instantiation of join somewhere else and does something unexpected as a result.

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brandon s. allbery [solaris,freebsd,perl,pugs,haskell] allbery@kf8nh.com

system administrator [openafs,heimdal,too many hats] allbery@ece.cmu.edu

electrical and computer engineering, carnegie mellon university    KF8NH