此F＃代码不起作用

Question

This is not working... I get error FS0001: The type 'string' is not compatible with the type 'seq' for the last line. Why?

let rec Parse (charlist) =
   match charlist with
   | head :: tail -> printf "%s " head
                     Parse tail
   | [] -> None

Parse (Seq.toList "this is a sentence.") |> ignore

Answer 1

The problem is that printf "%s " head means that head must be a string , but you actually want it to be a char , so you'll see that Parse has inferred type string list -> 'a option . Therefore, F# expects Seq.toList to be applied to a string seq , not a string .

The simple fix is to change the line doing the printing to printf "%c " head .