[Haskell-cafe] Magic values

MarLinn monkleyon at gmail.com
Sat Jul 8 17:40:05 UTC 2017

> You can avoid the underscores by defining the constants as pattern 
> synonyms so that they are syntactically more like constructors. This 
> also, of course, allows you to use them as patterns, which can also be 
> nice for constants.
>     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

Nice! This seems a bit evil, and not a full substitute. But it also 
helps hijack syntax highlighting, and it forces users to use a 
recent-ish version of GHC. I consider that A Good Thing™.

Now… as everything is “constant” in Haskell, on to define everything in 
capital letter patterns and return to good old COBOL times!

🍺 Wohoo!


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