Seq.filter with accumulator

Seq.filter with accumulator, without using mutable or ref.

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open System.Collections.Generic 

let filter (acc:'a) (f:('a -> 'b -> bool * 'a)) (s:'b seq) = 
    let rec iter (acc:'a) (e:IEnumerator<'b>) = 
        match e.MoveNext() with
        | false -> Seq.empty 
        | true -> match f acc e.Current with
                  | (true,newAcc) -> seq { yield e.Current; yield! iter newAcc e}
                  | (false,newAcc) -> seq { yield! iter newAcc e}
    iter acc (s.GetEnumerator())

//Example usage
[1;2;3;4;5] |> filter 0 (fun a b -> let newA = a + 1
                                    if newA > 3 then (true,newA)
                                    else (false,newA))
|> Seq.iter (fun i -> printfn "%d" i)

namespace System

namespace System.Collections

namespace System.Collections.Generic

val filter : acc:'a -> f:('a -> 'b -> bool * 'a) -> s:seq<'b> -> seq<'b>

Full name: Script.filter

val acc : 'a

val f : ('a -> 'b -> bool * 'a)

type bool = System.Boolean

Full name: Microsoft.FSharp.Core.bool

val s : seq<'b>

Multiple items
val seq : sequence:seq<'T> -> seq<'T>

Full name: Microsoft.FSharp.Core.Operators.seq

--------------------
type seq<'T> = IEnumerable<'T>

Full name: Microsoft.FSharp.Collections.seq<_>

val iter : ('a -> IEnumerator<'b> -> seq<'b>)

val e : IEnumerator<'b>

type IEnumerator<'T> =
member Current : 'T

Full name: System.Collections.Generic.IEnumerator<_>

System.Collections.IEnumerator.MoveNext() : bool

module Seq

from Microsoft.FSharp.Collections

val empty<'T> : seq<'T>

Full name: Microsoft.FSharp.Collections.Seq.empty

property IEnumerator.Current: 'b

val newAcc : 'a

IEnumerable.GetEnumerator() : IEnumerator<'b>

val a : int

val b : int

val newA : int

val iter : action:('T -> unit) -> source:seq<'T> -> unit

Full name: Microsoft.FSharp.Collections.Seq.iter

val i : int

val printfn : format:Printf.TextWriterFormat<'T> -> 'T

Full name: Microsoft.FSharp.Core.ExtraTopLevelOperators.printfn

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More information

Link:	http://fssnip.net/4y
Posted:	13 years ago
Author:	Ankur Dhama
Tags:	sequences