SML/NJ Read next character from file ignoring whitespace

Question

Can you give me a solution to create a function that reads the next character in a file stream, ignoring whitespace? (in SML/NJ).

Answer 1

You need to use the following libraries:

Char for your whitespace needs.

Text_IO for your streaming needs.

The following code is an example, which is not my finest code :)

let 
    (* Use TextIO library to open instream to file *)
    val ins = TextIO.openIn("C:\\Test.txt")

    (* This function takes the instream, and repeats 
        calling itself untill we are the end of the file *)
    fun handleStream (ins : TextIO.instream) =
        let 
            (* Read one character, hence the name, input1*)
            val character = TextIO.input1 (ins)

            (* This function decides whether to close the stream
                or continue reading, using the handleStream function 
                recursively.
            *)
            fun helper (copt : char option) =
                case copt of 
                    (* We reached the end of the file*)
                    NONE => TextIO.closeIn(ins)
                    (* There is something! *)
                  | SOME(c) => 
                        ((if (Char.isSpace c) 
                            then
                                (*ignore the space*)
                                ()
                            else
                                (* Handle the character c here *)
                                ())
                        (* Recursive call *)
                        ; handleStream(ins))
        in
            (* start the recursion *)
            helper (character)
        end
in
    (* start handling the stream *)
    handleStream( ins )
end