DebugWarning

Debug uses Custom Type Errors to warn the developer when it is being used.

Let's examine it further since it provides an example for us to follow should we wish to do something similar in the future. The source code is here, but we'll provide type signatures for the parts we need below and explain their usage:

-- See the copyright notice at the bottom of this file for this code:

-- | Nullary type class used to raise a custom warning for the debug functions.
class DebugWarning

instance Warn (Text "Debug usage") => DebugWarning

foreign import trace :: forall a b. DebugWarning => a -> (Unit -> b) -> b

-- same idea as 'trace' for all the other functions

In short, rather than writing function :: Warn (Text "Debug usage") => [function's type signature] on every function, they use an empty type class whose sole instance adds this for every usage of that type class.

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Copyright (c) 2015 Gary Burgess

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