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! Cheers, MarLinn