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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:5 years ago
Author:Ankur Dhama
Tags: sequences