teeF :: (a -> [Char]) -> [Char] -> F a a
teeF showf prefix
teeF
is an identity fudget which as a side effect prints the messages
that pass through it on the standard error output.
This can be helpful when debugging fudgets.
showf :: a -> [Char]
prefix :: [Char]
trace
in the hbc_library module NonStdTrace.