List.scanBack<'T,'State> Function (F#)
Visual Studio 2012
Like List.foldBack, but returns both the intermediate and final results.
Namespace/Module Path: Microsoft.FSharp.Collections.List
Assembly: FSharp.Core (in FSharp.Core.dll)
// Signature:
List.scanBack : ('T -> 'State -> 'State) -> 'T list -> 'State -> 'State list
// Usage:
List.scanBack folder list state
The following code example shows how to use List.scanBack, and also contrasts its behavior with List.scan.
// A list of functions that transform // integers. (int -> int) let ops1 = [ (fun x -> x + 1), "add 1" (fun x -> x + 2), "add 2" (fun x -> x - 5), "subtract 5" ] let ops2 = [ (fun x -> x + 1), "add 1" (fun x -> x * 5), "multiply by 5" (fun x -> x * x), "square" ] // Compare scan and scanBack, which apply the // operations in the opposite order. let compareOpOrder ops x0 = let ops, opNames = List.unzip ops let xs1 = List.scan (fun x op -> op x) x0 ops let xs2 = List.scanBack (fun op x -> op x) ops x0 printfn "Operations:" opNames |> List.iter (fun opName -> printf "%s " opName) printfn "" // Print the intermediate results. let xs = List.zip xs1 (List.rev xs2) printfn "List.scan List.scanBack" for (x1, x2) in xs do printfn "%10d %10d" x1 x2 printfn "" compareOpOrder ops1 10 compareOpOrder ops2 10
Output
Operations:
add 1 add 2 subtract 5
List.scan List.scanBack
10 10
11 5
13 7
8 8
Operations:
add 1 multiply by 5 square
List.scan List.scanBack
10 10
11 100
55 500
3025 501
