Alexander Vodomerov wrote:
> import Debug.Trace
>
> main = do
> putStrLn "xxx"
> return (trace "yyy" ())
> putStrLn "zzz"
>
> only xxx and zzz is displayed. yyy is missing.
> Why trace is not working?
Nothing uses the value of (trace "yyy" ()), so it is never
evaluated.
Try this instead, which uses the value for a pattern match:
() <- return (trace "yyy" ())
Or this, which makes the trace part of the sequence of IO
actions:
trace "yyy" (return ())
HTH,
Tom
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