Seq.init<'T> Function (F#)

Generates a new sequence which, when iterated, will return successive elements by calling the given function, up to the given count.

Namespace/Module Path: Microsoft.FSharp.Collections.Seq

Assembly: FSharp.Core (in FSharp.Core.dll)

// Signature:
Seq.init : int -> (int -> 'T) -> seq<'T>

// Usage:
Seq.init count initializer


  • count
    Type: int

    The maximum number of items to generate for the sequence.

  • initializer
    Type: int -> 'T

    A function that generates an item in the sequence from a given index.





Thrown when count is negative.

Return Value

The result sequence.


The results of calling the function will not be saved, that is, the function will be reapplied as necessary to regenerate the elements. The function is passed the index of the item being generated.

This function is named Initialize in compiled assemblies. If you are accessing the function from a language other than F#, or through reflection, use this name.

Thread Safety

The returned sequence may be passed between threads safely. However, individual IEnumerator values generated from the returned sequence should not be accessed concurrently.


The following example demonstrates the use of Seq.init to create a sequence of the first five multiples of 10.

let seqFirst5MultiplesOf10 = Seq.init 5 (fun n -> n * 10)
Seq.iter (fun elem -> printf "%d " elem) seqFirst5MultiplesOf10
0 10 20 30 40


Windows 7, Windows Vista SP2, Windows XP SP3, Windows XP x64 SP2, Windows Server 2008 R2, Windows Server 2008 SP2, Windows Server 2003 SP2

Version Information

F# Runtime

Supported in: 2.0, 4.0


Supported in: 3

See Also


Collections.Seq Module (F#)

Microsoft.FSharp.Collections Namespace (F#)