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No side effects/change state.
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I have been programming for 40 years, C, C , Java, C#, Python, Perl, Tcl and many others, all imperative.
My understanding is FP does not allow for side effects so how do you get anything done? If you cannot effect the system, what are you doing? You would not be able to display anything on the screen, message another app, or just about anything.
What am I missing?
Thank you
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I think we need more emphasis on the "side" part of the term "side effects". Is printing to the screen a side-effect? IO is not a side effect, just an effect. A side-effect would be using a variable that has changed in value without you knowing about it, due to some opaque process hidden from the programmer. Lack of side effects could be described as referential transparency -- the idea that your variables don't change from underneath you (e.g. if you evaluate x to be 5, it's always 5 as long as you're looking at the same x).