The problem is that your code still isn't lazy enough: the arguments to Seq.append
are evaluated before the result can be accessed, but evaluating the second argument (Seq.map2 ...
) requires evaluating its own arguments, which forces the same lazy value that's being defined. This can be
worked around by using the Seq.delay
function. You can also forgo the lazy
wrapper, and list
s are already seq
s, so you don't need Seq.ofList
:
let rec fibs =
Seq.append [0;1]
(Seq.delay (fun () -> Seq.map2 (+) fibs (Seq.skip 1 fibs)))
However, personally I'd recommend using a sequence expression, which I find to be more pleasant to read (and easier to write correctly):
let rec fibs = seq {
yield 0
yield 1
yield! Seq.map2 (+) fibs (fibs |> Seq.skip 1)
}