... and I have no idea how this is supposed to work. Even for primitive
recursion
factorial : Int -> Int
factorial x =
Trampoline.evaluate (fac x)
fac : Int -> Trampoline Int
fac x =
if x <= 0 then
Trampoline.done 1
else
Trampoline.jump
(\_ ->
???
)
On Tue, Jul 12, 2016 at 7:25 AM, Nick H <[email protected]> wrote:
> Ian, that is a great thought, but even if we split the list exactly in
> half, the call stack fills up when the list length gets to around 4500.
>
> partition _ list =
> let
> n = List.length list // 2
> in
> (List.take n list, List.drop n list)
>
> In my specific problem, the "wrap" function finds the smallest rectangular
> prism that encloses a set of 3D points. The "partition" function splits the
> list of points in half, with a plane that is aligned with one of the box's
> axes. I have a lot of tests to ensure the function doesn't break in weird
> cases, like all of the points being identical. So I am pretty sure the
> partition is doing a reasonable split.
>
> I am taking a look at the trampoline library now...
>
> On Tue, Jul 12, 2016 at 12:03 AM, Janis Voigtländer <
> [email protected]> wrote:
>
>> Maybe the Trampoline library can help you?
>>
>> http://package.elm-lang.org/packages/elm-lang/trampoline/1.0.0/Trampoline
>>
>>
>> Am Dienstag, 12. Juli 2016 schrieb Nick H :
>>
>>> Here is a puzzle for you:
>>>
>>> For a large enough list, the code below will fill up the call stack and
>>> crash. It makes sense that the Elm compiler can't optimize it with tail
>>> calls, since the recursive function gets called more than once per
>>> iteration.
>>>
>>> What is the best way to rewrite this without using recursion?
>>>
>>>
>>>
>>> type Tree = Leaf Foo | Node Bar Tree Tree
>>>>
>>>> create : List Foo -> Tree
>>>> create faces =
>>>> case faces of
>>>> [] ->
>>>> dummyFoo
>>>>
>>>> foo :: [] ->
>>>> Leaf f
>>>>
>>>> list ->
>>>> let
>>>> box = wrap list
>>>>
>>>> ( left, right ) = partition box list
>>>> in
>>>> Node box (create left) (create right)
>>>>
>>>> wrap : List Foo -> Bar
>>>>
>>>> partition : Bar -> List Foo -> (List Foo, List Foo)
>>>>
>>>> --
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>
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