Axel Jantsch wrote:
>>gibs = 1 : 1 : (zipWith f gibs (tail gibs))
>> where f x y = min (x + y) 10
>
>[...] how can I force the garbage collector to reclaim the
>memory of the head of the list after I have processed it, since I will
>never ever reference it again?
There's no entirely satisfactory way to do this. The language standard doesn't specify caching behavior, so you have to rely on the way that actual implementations handle caching.
I think it's safe in practice to assume that a binding inside a function won't be cached across call boundaries, even if the value of the binding doesn't depend on the function argument. I.e. you should be able to solve your problem with
makeGibs () = gibs where
gibs = 1 : 1 : (zipWith f gibs (tail gibs))
f x y = min (x + y) 10
In principle a compiler could float the definition of gibs outside the function makeGibs and cache it across calls, but I don't think any compiler will actually do this, precisely because it makes this trick stop working.
A more elegant variation which definitely won't be cached is
gibsFrom a b = gibs where gibs = a : b : (zipWith f gibs (tail gibs)) f x y = min (x + y) 10
In both cases Hugs seems to consume the memory at the same rate as the
original program.
Jerzy Karczmarczuk
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