stemming of a word without Regex

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")