Documentation

If you're running into this class, then you need to add RequireCallStack to your function's signature, or discharge the constraint using provideCallStack.

I'd like to provide a TypeError instance here with a good message, but unfortunately, I won't be able to do that because it fails early. I need Unsatisfiable in GHC 9.8 for that. So, until I get that, you'll have to see an error message that smuggles the suggestion in:

No instance for 'Add_RequireCallStack_ToFunctionContext_OrUse_provideCallStack'

Which, hey, it is better than nothing!

Since: 0.1.0.0

An alias to make referring to Add_RequireCallStack_ToFunctionContext_OrUse_provideCallStack easier, since it is a bit of a mouthful.

If you see this, you probably need to either add RequireCallStack to the function constraints, or you need to call provideCallStack to discharge it.

Since: 0.1.0.0

An internal detail. This is a specialization of the trick used in the reflection library to reify constraints. It's based on some GHC trickery - notably, that dictionaries become runtime parameters, and a no method dictionary has the same runtime rep as ().

Since: 0.1.0.0

Satisfy a RequireCallStack constraint for the given block. Can be used instead of propagating a RequireCallStack up the call graph.

Usage:

main :: IO ()
main = do
  provideCallStack $ do
      errorRequireCallStack "hello"

Note how main does not have a HasCallStack or RequireCallStack constraint. This function eliminates them, so that errorRequireCallStack can be called without compilation error.

Since: 0.1.0.0