How to best add logging/debugging code?
simonmar at microsoft.com
Fri Nov 28 13:49:57 EST 2003
> Hmm. This suggestion has the potential to confuse the casual user
> even more. Consider
> debug s x = trace (s++": "++show x++"\n") x
> f x = debug ("entered f") (... g y ...)
> g y = debug ("entered g") (...)
> main = ... f ...
> With the current definition of 'trace', although the formatting is
> ugly, the user (correctly) sees that the evaluation of f is entered
> before g.
> entered f: entered g: val_g_y
The current implementation of Debug.Trace does indeed do this, but the
behaviour can be altered by changing the buffering mode of stderr. Try
main = do
hSetBuffering stderr (BlockBuffering Nothing)
trace ("a" ++ trace "b" "") (return ())
AFAIK, it's been this way for a long time.
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