Consider making throw and throwIO strict
It's possible for code to throw an exception that itself throws an imprecise exception. Such an exception is tricky to catch. For example:
import Control.Exception
strange = throwIO (undefined :: SomeException) `catch` \ex ->
case () of
_ | Just _ <- (fromException ex :: Maybe IOError) -> print "IOError"
| otherwise -> print "Something else"
You might think that this would catch the exception and print "Something else", but in fact it does not. If others think this is as surprising as I do, perhaps we should make throwIO
and throw
strict, so an exception will never itself be bottom. Using
throwIO' !e = throwIO e
in the code above instead of throwIO
allows the exception to be caught.
Trac metadata
Trac field | Value |
---|---|
Version | 8.1 |
Type | FeatureRequest |
TypeOfFailure | OtherFailure |
Priority | normal |
Resolution | Unresolved |
Component | Core Libraries |
Test case | |
Differential revisions | |
BlockedBy | |
Related | |
Blocking | |
CC | |
Operating system | |
Architecture |