forever contains a space leak

1. 9.0.0's forever (implemented in terms of Applicative) has a space leak for certain base Monads. The old forever (implemented in terms of Monad) does not.

See these messages for details

• https://mail.haskell.org/pipermail/haskell-cafe/2016-October/125177.html
• https://mail.haskell.org/pipermail/haskell-cafe/2016-October/125178.html
• https://mail.haskell.org/pipermail/haskell-cafe/2016-November/125443.html

This is not necessarily forever's fault. It seems likely that the broken behaviour that occurs with ReaderT and StateT (on IO) could be fixed by a specialised implementation of *> (for ReaderT and StateT).

Perhaps, then, this bug should ultimately be fixed in transformers (and various other packages which supply Applicatives) but it is a regression introduced by base-4.9.0.0 so I think it's worthwhile to discuss here.

Trac metadata

Trac field	Value
Version	8.0.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	libraries/base
Test case
Differential revisions
BlockedBy
Related
Blocking
CC
Operating system
Architecture

changed weight to 5

added Tbug Trac import core libraries labels

I confirm that the space leak is gone for ReaderT of IO if I define

f *> v  = ReaderT $ \ r -> runReaderT f r *> runReaderT v r

I presume (but haven't checked) that the space leak is also gone for StateT of IO if the corresponding implementation for *> is given in the Applicative instance.

Adding Edward and the core libraries committee; it's their territory.

Trac metadata

Trac field	Value
CC	- → core-libraries-committee@haskell.org

Ultimately I conclude that the issue lies in transformers, not base. I filed this issue on transformers:

http://hub.darcs.net/ross/transformers/issue/33

The transformers patch has been merged. Let's hope that Ross releases soon so we can bump the submodule included in 8.0.2.

closed

Trac metadata

Trac field	Value
Resolution	Unresolved → ResolvedInvalid

added runtime perf label

added Pnormal label