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Generating sequences recursively. Is it possible?
f#

I would like to write a tail recursive function with signature

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f: int -> seq<int>

that each call should do something with its input, yield a value and than call itself recursively. I used Seq.append:

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let rec sequence input =

    Seq.append

        (Seq.singleton input)

        (sequence (input + 1))

Can it be made tail recursive?

.

Something that would do what you want without killing the stack would be

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let rec sequence input =
    seq {
        yield input //or yield f input, if you want to transform the input
        yield! sequence (input+1) //last call --> tail recursive
    }

Somewhat harder to read, but faster, is using Seq.unfold:

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let sequence2 input = Seq.unfold (fun n -> Some (n,n+1)) input
By on 2/8/2010 1:02 AM ()

Thanks. That's exactly what I was looking for.

By on 2/9/2010 11:55 AM ()

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