[Haskell] reasons for non-portability

[Wolfgang Jeltsch]

Hello,

according to
    http://www.haskell.org/hierarchical-modules/libraries/
    reference-libraries.html#MODULE-HEADER,
each module should have a header which contains a line about portability.  My 
question is, if a module is considered non-portable only if it contains 
non-portable constructs itself, or if a module is also non-portable if it 
just imports a module which is non-portable.

Wolfgang