Seq.fold<'T,'State> Function (F#)

Applies a function to each element of the collection, threading an accumulator argument through the computation. If the input function is f and the elements are i0...iN, then this function computes f (... (f s i0)...) iN.

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

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

// Signature:
Seq.fold : ('State -> 'T -> 'State) -> 'State -> seq<'T> -> 'State

// Usage:
Seq.fold folder state source

Parameters

• folder
  Type: 'State -> 'T -> 'State

  A function that updates the state with each element from the sequence.

• state
  Type: 'State

  The initial state.

• source
  Type: seq<'T>

  The input sequence.

Exceptions

Return Value

The final result of the computation.

Remarks

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

Example

The following code shows how to use Seq.fold to implement a function that computes the sum of the elements of a sequence.

let sumSeq sequence1 = Seq.fold (fun acc elem -> acc + elem) 0 sequence1
Seq.init 10 (fun index -> index * index)
|> sumSeq
|> printfn "The sum of the elements is %d."

Output

The sum of the elements is 285.

Platforms

Windows 8, Windows 7, Windows Server 2012, Windows Server 2008 R2

Version Information

F# Core Library Versions

Supported in: 2.0, 4.0, Portable

See Also

Reference

Collections.Seq Module (F#)

Microsoft.FSharp.Collections Namespace (F#)