On Fri, Oct 5, 2012 at 2:04 PM, Gabriel Gonzalez
Here's the problem: WriterT always leaks space. I've tested three ways to fix the space leak, and only one works:
* [DOES NOT WORK] Add a strictness annotation to the Monad instance for WriterT * [DOES NOT WORK] Use the StateT monad transformer *without* a strictness annotation * [WORKS] Use the StateT monad transformer *with* a strictness annotation
Long ago, I had the same problem, and went through the same three attempts before settling on the last one. With help from kind people on haskell-cafe (probably findable in the archives). So I support putting it in libraries along with comments about why, so that future generations need not go through the same process. Then we can tell them about how we had to walk in the snow both ways uphill fighting space leaks with bare hands while they just have to read about it. For the same reason I support State.modify' :)