Question

In Microsoft’s F# samples, they use the “>>” operator as follows:

test |> Seq.iter (any_to_string >> printfn "line %s");

What does the “>>” operator do in this context? Is each item of the sequence (an array in this case) get passed to any_to_string implicitly? Is this similar to (fun item -> printfn "line %A" item)?

Answer 1

An equivalent piece of code could be written the following way:

test |> Seq.iter(fun x -> printfn "line %s" (any_to_string x))

In other words, the >> operator simply does this: given a function f(x) returning type T and g(y) with y being of type T, you can use f >> g to create a function h(z) being equivalent to g(f(x)). No argument but the inner and outer function has to be passed to that operator and the result is a function which can be applied at any time in your code, so you could do this:

//myFunc accepts any object, calls its ToString method, passes ToString
//result to the lambda which returns the string length. no argument is
//specified in advance
let myFunc = any_to_string >> (fun s -> s.Length)
let test = 12345
let f = 12345.0
//now we can call myFunc just like if we had definied it this way:
//let myFunc (x:obj) = obj.ToString().Length
printfn "%i" (myFunc i)
printfn "%i" (myFunc f)