FSharp F＃中的字符串编辑问题

Question

I'm quite new to the F# language and functional first approach, as I have only been working with Object Oriented languages.

Im trying to create a simple Word Guesser Console Application. The feature i'm working on is to be able to guess for multiple characters at once

I have a hard time piecing together a nice way to do this, as i want to take a functional approach, and always end up having issues with immutable arrays and such.

Here is what I have come up with:

Im trying to replace/reveal the chars on the indexes of the given word, which corresponds the guess and return the resulting string

Any Leads?

Kindly Regards Kalrin

Answer 1

A functional way easy to get would be to use a match but to regenerate a new string.

You may also want to use a Some/None (which will give you an option string as a result of your function if you look at its signature, this is a functional way to write it but if you need an empty chain, you can also return one). Please refer to the bible for F# fsharpforfunandprofit.com

A few comments:

• OOP in .Net (let's say C#) : You would use Substring method instead of your for loop
• Be careful, Substirng can return an exception (if you put your mouse on it, it tells you so in the messagebox) and to avoid any issue at run time (as we usually do not work with exceptions in F# - cf Railway programming on fsharpforfunandprofit), you need a second match to check the length.

https://fsharpforfunandprofit.com/posts/the-option-type/

let stringContains (word:string) (hidden:string) (guess:string) =
    match word.IndexOf(guess) with
    | -1 -> None
    | ind -> match (hidden.Length < ind) with
                     | true -> Some (guess)
                     | false -> Some (hidden.Substring(0, ind) + guess)