I'm learning F#, and I am having trouble understanding why this crashes. It's an attempt to solve Project Euler problem 2.
let rec fibonacci n =
if n = 1 then
1
elif n = 2 then
2
else
fibonacci (n - 1) + fibonacci (n - 2)
let debugfibonacci n =
printfn "CALC: %d" n
fibonacci n
let isEven n =
n % 2 = 0
let isUnderLimit n =
n < 55
let getSequence =
//[1..30]
Seq.initInfinite (fun n -> n)
|> Seq.map debugfibonacci
|> Seq.filter isEven
|> Seq.takeWhile isUnderLimit
Seq.iter (fun x -> printfn "%d" x) getSequence
The final version would call a sum function (and would have a higher limit than 55), but this is learning code.
As is, this gives a StackOverflowException. However, if I comment in the [1..30] and comment out the Seq.initInfinite, I get:
CALC: 1
CALC: 2
2
CALC: 3
CALC: 4
CALC: 5
8
CALC: 6
CALC: 7
CALC: 8
34
CALC: 9
CALC: 10
CALC: 11
It appears to be generating items on demand, as I would expect in LINQ. So why does it blow up when used with initInfinite?
