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Continue sequence after applying Seq.takeWhile, skip, take, etc

Sometimes you need to take more elements from a sequence, e.g. look at https://stackoverflow.com/questions/12562327/how-to-do-seq-takewhile-one-item-in-f This solution allows fetching elements from the same sequence after applying takeWhile, skip, take and other sequence functions. However, need to remember to call function with right parameter: use 'true' to include current element into result sequence (after takeWhile for example)

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/// allows fetching elements from same sequence
type ContinueSequence<'a> (xs: 'a seq) =
    let en = xs.GetEnumerator()

    member _.Continue (includeCurrent: bool) =
        let s = seq { while en.MoveNext() do yield en.Current }
        let c = seq { en.Current }
        if includeCurrent then
            Seq.append c s
        else
            s

    interface IDisposable with 
        member _.Dispose() =
            en.Dispose()

/// usage example:
let a = seq [1; 2; 3; 4; 5; 6; 7]

use seq = new ContinueSequence<_>(a)
let s1 = seq.Continue(false) |> Seq.takeWhile((>) 3) // take 1 and 2, 3 is current
let s2 = seq.Continue(true) |> Seq.take(2)    // take 3 and 4
let s3 = seq.Continue(false) |> Seq.skip(1)   // skip 5

let s = 
	s1 
	|> Seq.append <| s2 
	|> Seq.append <| s3 
	|> Seq.toList

// s = [1; 2; 3; 4; 6; 7]
Multiple items
val seq : sequence:seq<'T> -> seq<'T>

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

--------------------
type seq<'T> = System.Collections.Generic.IEnumerable<'T>

Full name: Microsoft.FSharp.Collections.seq<_>
type bool = System.Boolean

Full name: Microsoft.FSharp.Core.bool
module Seq

from Microsoft.FSharp.Collections
val append : source1:seq<'T> -> source2:seq<'T> -> seq<'T>

Full name: Microsoft.FSharp.Collections.Seq.append
val takeWhile : predicate:('T -> bool) -> source:seq<'T> -> seq<'T>

Full name: Microsoft.FSharp.Collections.Seq.takeWhile
val take : count:int -> source:seq<'T> -> seq<'T>

Full name: Microsoft.FSharp.Collections.Seq.take
val skip : count:int -> source:seq<'T> -> seq<'T>

Full name: Microsoft.FSharp.Collections.Seq.skip
val toList : source:seq<'T> -> 'T list

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

More information

Link:http://fssnip.net/7XL
Posted:1 month ago
Author:Ruslan Enikeev
Tags: infinite sequence , seqences , sequence , sequence expressions , sequences skip