IO exception: A web handler threw an exception. Details: no value about snap-core HOT 2 CLOSED

I found the cause of my error:

When using evalSnap, the function throwError :: MonadSnap m => ServantErr -> m a from servant-snap doesn't work. Instead of getting the HTTP error that I specify, I get the IO exception above (throwIO $ ErrorCall "no value").

I don't know whether this problems originiates in evalSnap and thus snap-core or within throwError and thus servant-snap.

I also don't know whether this is tolerated behavior. Maybe evalSnap isn't meant to be used with throwError. Maybe I can safely switch to runSnap.

I am currently working with snap-core-1.0.4.1 and snap-server-1.1.1.2 and can't easily swap out either of them.

from snap-core.

Given that the documentation of servant-snap states

throwError :: MonadSnap m => ServantErr -> m a

Terminate request handling with a ServantErr via finishWith

... and evalSnap has a very specific use, not a general one, I conclude this is by no means a bug. I guess I would prefer a variant of evalSnap that evaluates to IO (Maybe a) or something instead of throwing IO exceptions.

from snap-core.