Hello Udo, Sunday, October 22, 2006, 6:41:24 PM, you wrote:
Now, the state will not be entirely consumed/evaluated by the user, and so it will not become garbage. Am I right?
No. The state cannot become garbage, because there is still a reference to it. As long as runStateT has not returned, any part of the state can still be accessed, so it is not garbage.
this monad state is not something fixed, it's completely replaced by each setState call (and old state becomes garbage from this moment). in particular, with this toy example, after reading each next file, old file contents continue its life as garbage
Completely evaluating the state will not reduce memory consumption in your case, because the list of lists won't be substantially smaller that the thunk to create it. In fact, evaluating this thunk will consume memory.
while this is true for this particular data (i.e., getContents >>= lines) in general this is not true. f.e. [[toUpper 'a']] list will need more memory in unevaluated form
Where should I force evaluation?
You can't. Your state really is that large, at least in the toy example. You'd need a different data structure ((Array Int ByteString) or (Map Int ByteString) come to mind) and then make that strict.
[ByteString] will be enough. Andrea, may be you can convert strings to bytestrings after hxt conversion? -- Best regards, Bulat mailto:Bulat.Ziganshin@gmail.com