Given this functionlet readInput() =   Seq.initInfinite (fun _ -> Console.ReadLine()) |> Seq.takeWhile (fun s -> s <> null) ` |> Seq.map int`is the _ in the function called by Seq.initInfinite a wild card, so that anything can be read off STDIN?I've got a couple of different F# books, and am looking on the Internet, but can only find references to _ being used in unpacking tuple values. 
Is the _ character in the first anonymous function a wildcard?
f#
is the _ in the function called by Seq.initInfinite a wild cardYes.so that anything can be read off STDINNo. Seq.initInfinite passes an int, indicating the current index. For example, you can use it to create an infinite sequence of only even numbers: Seq.initInfinite (fun i -> i * 2). But in your case, you don't care about the index, so using _ is appropriate here.Using the wildcard here does not affect the Console.ReadLine() in any way.