On Sunday, 31 August 2014 at 06:11:56 UTC, Marco Leise wrote:
Am Sun, 31 Aug 2014 01:09:32 +0000
schrieb "Ola Fosheim Grøstad"
<[email protected]>:
How does logging interact with pure? You need to be able to
log in pure functions.
How do you come to that conclusion? Purity is a synonym for
_not_ having side effects. That said - as usual - "debug"
statements allow you to punch a hole into purity.
1. ~90% of all functions are weakly pure, if you cannot log
execution in those functions then logging becomes a liability.
2. If you define logging in a weakly pure function as tracing of
execution rather than logging of state, then you can allow
memoization too.
3. You don't normally read back the log in the same execution,
state is thus not preserved through logging within a single
execution. It has traits which makes it less problematic than
general side effects that change regular global variables.
