Example
Pipe operators are used to pass parameters to a function in a simple and elegant way. It allows to eliminate intermediate values and make function calls easier to read.
In F#, there are two pipe operators:
-
Forward (
|>): Passing parameters from left to rightlet print message = printf "%s" message // "Hello World" will be passed as a parameter to the print function "Hello World" |> print -
Backward (
<|): Passing parameters from right to leftlet print message = printf "%s" message // "Hello World" will be passed as a parameter to the print function print <| "Hello World"
Here is an example without pipe operators:
// We want to create a sequence from 0 to 10 then:
// 1 Keep only even numbers
// 2 Multiply them by 2
// 3 Print the number
let mySeq = seq { 0..10 }
let filteredSeq = Seq.filter (fun c -> (c % 2) = 0) mySeq
let mappedSeq = Seq.map ((*) 2) filteredSeq
let finalSeq = Seq.map (sprintf "The value is %i.") mappedSeq
printfn "%A" finalSeq
We can shorten the previous example and make it cleaner with the forward pipe operator:
// Using forward pipe, we can eliminate intermediate let binding
let finalSeq =
seq { 0..10 }
|> Seq.filter (fun c -> (c % 2) = 0)
|> Seq.map ((*) 2)
|> Seq.map (sprintf "The value is %i.")
printfn "%A" finalSeq
Each function result is passed as a parameter to the next function.
If you want to pass multiple parameters to the pipe operator, you have to add a | for each additional parameter and create a Tuple with the parameters. Native F# pipe operator supports up to three parameters (|||> or <|||).
let printPerson name age =
printf "My name is %s, I'm %i years old" name age
("Foo", 20) ||> printPerson
