Dear libraries, I am experimenting with the attached code, where right before the consumption by Vector.fromList, the list is unevaluated, and each element has a small type (a Double), but if left unevaluated before the list is traversed further, will hold on to a rather large portion of memory. I want to use the example in a talk about efficient Haskell next week. After consumption by (unboxed) Vector.fromList, the list has been traversed, but every element in the vector is still a huge thunk, thus holding on to 429MB maximum residency. If I just deepseq the hole list before converting it to a vector, the memory residency becomes 140MB, about what can be expected for a unboxed Vector Double with 3664891 entries plus the [Double] with 3664891 entries. The point of the exercise is to show that we get the best performance by evaluating the list value-strict, i.e. evaluate the head of the list before continuing, but still allowing the GC to remove the part of the list has has already been consumed by fromList, yielding a constant space behavior (not counting the final vector). This is actually motivated by a real-world experience of mine. So if I use this function: valueStrictList :: [a] -> [a] valueStrictList [] = [] valueStrictList (x:xs) = x `seq` (x:valueStrictList xs) before fromList, the maximum residency drops to 67MB, which is pretty good. (58MB is the pure cost of the resulting vector). Now I’d like to get the same result with the standard functions from Control.Seq, instead of rolling my own. I did not look in Control.Parallel.Strategies, as I am not interested in parallelization at this point. So I tried Seq.withStrategy (Seq.seqList Seq.rseq) but this has the same effect as deepseq (140MB), which is probably what was intended, but not what I need. So I did look at Control.Parallel.Strategies and found evalList, which sounds like what I want, but Strat.withStrategy (Strat.evalList Strat.rseq) caused a Stack space overflow, and even using the same function as before, but now from Strategies, i.e. Strat.withStrategy (Strat.seqList Strat.rseq) causes a stack overflow. My questions are: 1. Why is there no evalList in Control.Seq? Should it be there? 2. Why does seqList behave differently in Control.Parallel.Strategies and in Control.Seq? Is that a bug? The example code is attached, and the various options are easily tried out by commenting out the apropriate line. I’m using ghc-7.0.4 and parallel-3.1.0.1, and compiled the code with "-O2". Greetings, Joachim -- Joachim "nomeata" Breitner mail@joachim-breitner.de | nomeata@debian.org | GPG: 0x4743206C xmpp: nomeata@joachim-breitner.de | http://www.joachim-breitner.de/