[Haskell-beginners] Logging in Haskell
jason.dusek at gmail.com
Mon Mar 30 20:47:43 EDT 2009
In general, you can't do it -- there's no way to perform a
write to external logs in the midst of pure code. That would
mean it's not pure any more, consequently changing its type
signature and forcing you to rewrite a bunch of stuff. The
use of the GHCi debugger is highly recommended.
The first few times you use the debugger, you'll notice it
seems to go backward. That is laziness in action -- it goes
immediately to the result of an expression and then walks
backward as it is forced to evaluate the intermediate values.
Well, okay -- there is one way to do the logging like you
want; but it's dangerous. Use `unsafePerformIO` all over the
place and pray :)
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