EN04_Prompt

The .PromptWriter field allows you to set a function that creates the string that should be printed at the prompt.

※ Previously, this was specified in a field called Prompt, but this has been discontinued.

editor := &readline.Editor{
	// ;
	PromptWriter: func(w io.Writer) (int, error) {
		return io.WriteString(w, "\x1B[1;36m$ \x1B[0m") // print `$ ` with cyan
	},
	// ;
}

A Function set with .PromptWriter are evaluated every time a prompt is displayed. Please output the prompt to io.Writer using fmt.Fprintf etc..

The return value (int,error) is currently unused.

It was originally created with the intention of having the user provide the character width for the prompt. However, in many cases, the number of bytes != character width, which was essentially meaningless. So, the (*Editor) ReadLine method stores the output with strings.Builder and counts the width of it. Therefore you does not have to count now.