On 24 September 2010 15:21, Daniel Fischer
Proposal: A stricter implementation of lines.
Reason: The current implementation causes a space leak (cf. http://homepages.inf.ed.ac.uk/wadler/papers/leak/leak.ps), at least in GHC.
The proposed implementation fixes the leak at the small cost of being stricter if the first _|_ in the String is the first character of a line.
Discussion period: Three weeks, until 15th October (because of ICFP).
My gut instinct is that we should not make lines stricter. Generally the list library is as lazy as possible, except when there are compelling reasons otherwise. I am not yet convinced that this proposal meets that standard. Have we thought about the opposite issue, that there may be programs that rely on the current non-strict version for correctness or memory behaviour? We currently have an open proposal on making intersperse less strict because it caused practical problems (unexpected memory behaviour). There's also an issue of consistency with other functions in the list library. The lines function is similar in many ways to group / groupBy, and with the proposed change the strictness properties of these functions would be inconsistent. Such inconsistency has a cost in terms of programmers being able to predict and reason about strictness and space use (simply because if its inconsistent then it is harder to remember). The strictness of lines is pretty subtle. I think it would help our discussion if people reading this thread look at the strictness properties given in the ticket. Duncan