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Projecting lists
Three functions showing how to implement projection for functional lists. First version uses naive recursion and the second one is tail-recursive using the accumulator parameter. The third version extends this with continuation passing.
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/// Create a list containing results of calling
/// the function 'f' on all elements of the input 'list'
let rec map f list =
match list with
| x::xs -> (f x)::(map f xs)
| [] -> []
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/// Create a list containing results of calling
/// the function 'f' on all elements of the input 'list'
let map f list =
/// Inner recursive function that uses
/// accumulator argument to construct list
let rec mapAux acc list =
match list with
| x::xs -> mapAux ((f x)::acc) xs
| [] -> acc |> List.rev
mapAux [] list
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/// Create a list containing results of calling
/// the function 'f' on all elements of the input 'list'
let map f list =
/// Inner recursive function that uses
/// continuation argument to construct list
let rec mapAux cont list =
match list with
| x :: xs -> mapAux (fun ys -> f x :: ys |> cont) xs
| [] -> cont []
mapAux id list
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val map : f:('a -> 'b) -> list:'a list -> 'b list
Full name: Script.L1.map
Create a list containing results of calling
the function 'f' on all elements of the input 'list'
val f : ('a -> 'b)
Multiple items
val list : 'a list
--------------------
type 'T list = List<'T>
Full name: Microsoft.FSharp.Collections.list<_>
val x : 'a
val xs : 'a list
val map : f:('a -> 'b) -> list:'a list -> 'b list
Full name: Script.L2.map
Create a list containing results of calling
the function 'f' on all elements of the input 'list'
val mapAux : ('b list -> 'a list -> 'b list)
Inner recursive function that uses
accumulator argument to construct list
val acc : 'b list
Multiple items
module List
from Microsoft.FSharp.Collections
--------------------
type List<'T> =
| ( [] )
| ( :: ) of Head: 'T * Tail: 'T list
interface IEnumerable
interface IEnumerable<'T>
member Head : 'T
member IsEmpty : bool
member Item : index:int -> 'T with get
member Length : int
member Tail : 'T list
static member Cons : head:'T * tail:'T list -> 'T list
static member Empty : 'T list
Full name: Microsoft.FSharp.Collections.List<_>
val rev : list:'T list -> 'T list
Full name: Microsoft.FSharp.Collections.List.rev
val map : f:('a -> 'b) -> list:'a list -> 'b list
Full name: Script.L3.map
Create a list containing results of calling
the function 'f' on all elements of the input 'list'
val mapAux : (('b list -> 'c) -> 'a list -> 'c)
Inner recursive function that uses
continuation argument to construct list
val cont : ('b list -> 'c)
val ys : 'b list
val id : x:'T -> 'T
Full name: Microsoft.FSharp.Core.Operators.id
More information