[Haskell-cafe] Magic values, WAS: Encrypting streamed data

MarLinn monkleyon at gmail.com
Thu Jul 6 13:09:17 UTC 2017

> https://gist.github.com/snoyberg/20243aae347b38ad09daaf8b129e2efb
> It's got some magic values in a few places (especially that 65!)

Off topic, but sometimes when I find myself using magic values I 
can't/won't get rid off, I'll just apply the good old habits learned in 
Java times. For example you might find a section at the top of a file 
with things like

_DAYS_IN_A_WEEK_ , _KNOWN_SIZE_OF_POINT_ :: INT-- | Seems to be a good 
approximation for now _DAYS_IN_A_WEEK_ = 7 -- | When you ask "What's the 
point", this will not answer your question. _KNOWN_SIZE_OF_POINT_ = 65

Uppercase makes it easy to identify these as constants/magic values. The 
underscore in front works as an initial lowercase letter so they can be 
used as values despite uppercase.

The goal is not necessarily to make these values easy to change, but to 
add documentation to usage sites.

It's unnecessary In such a quick demonstration, but I wanted to take the 
opportunity to throw in my _VALUE_OF_CONTRIBUTION_IN_CENTS_ cents 
because I haven't seen others do something like this.


PS: The underscore does introduce its own error message though.

     • Found hole: _VALUE_OF_CONTRIBUTION_IN_CENTS_ :: Double
       Or perhaps ‘_VALUE_OF_CONTRIBUTION_IN_CENTS_’ is mis-spelled, or not in scope

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