pretty-error alternatives and similar packages
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Sometimes you need to assume something at runtime that you can't prove in the type system. When you do that, you should make sure you get a good error message if ever your assumption turns out to be wrong. That's what this library is for.
Use the functions in here to get high quality error messages for when your invariants don't hold at runtime. The functions all pretty print any Haskell values given to them, which makes it easier to understand what's going on when your code breaks.
assertRight for a successful assertion:
>>> assertRight "Example message" (Right 42) 42
assertRight for a failed assertion:
>>> assertRight "Example message" (Left "unexpected error") *** Exception: Example message: "unexpected error"
fromRight to unpack an
Either that is actually a
>>> fromRight (Left ["foo","bar","baz"]) *** Exception: [ "foo" , "bar" , "baz" ]