Question

Is it possible to stem words without using Regex in F#?

I want to know how can I write a F# function which inputs a string and stems it.

eg.

input = "going"
output = "go"

I can’t find a way to write the code without using the regex: .*ing\b and replace function which would be almost like doing in C# without any advantage.

Semi pseudo code of what I am trying to write is:

let stemming word = 
   match word
    |(word-"ing")+ing -> (word-"ing")

Answer 1

Here is a function applying the simplest stemming rule:

let (|Suffix|_|) (suffix: string) (s: string) =
    if s.EndsWith(suffix) then
        Some(s.Substring(0, s.Length - suffix.Length))
    else
        None

let stem = function
    | Suffix "ing" s -> s
    | _ -> failwith "Not ending with ing"

Parameterized active patterns makes pattern matching more readable and more convenient in this case. If stemming rules get complicated, you could update active patterns to keep the stem function unchanged.