Anton van Straaten
Exactly. I'm worried about, e.g. needing to use something as simple as a stream of [...]
Haskell lets you easily create "infinite" lists, which is a powerful and useful feature.
This has bit me on several occasions, and I think streaming over an infinite list with too little strictness has been the cause of most of my space "leaks". I've become pretty good at spotting this in advance now, so I no longer need to whip out the profiling as often. The archetypical case is parsing a large file into a non-strict data structure. The data structure will then tend to hang onto the whole input, instead of the result, which typically is much more compact. Making the data structure strict solves the problem.
It'd be a stretch to characterize this as "hard".
I guess it's hard in the sense that a) it's something different from what you need to think about in other languages, and b) it's not really an error, so you don't get as much help from the compiler or RTS.
I don't see much connection between this and the space efficiency of long-running programs.
Except a long-running program could be doing something like parsing a conceptually infinite input stream. -k -- If I haven't seen further, it is by standing in the footprints of giants