I need to create a function that receives a string and checks if the last char is a "\n" or not. If so, returns the same string without it's last char. The ways I can think of doing this are not the slightest efficient. I need it to be efficient.
It's hard to give a precise answer to your question as you do not give any context.
The simplest solution I can think of is:
let check s = let n = String.length s in if n > 0 && s.[n-1] = '\n' then String.sub s 0 (n-1) else s