How can I remove duplicates in an F# sequence without using references

Question

I have a sorted sequence and want to go through it and return the unique entries in the sequence. I can do it using the following function, but it uses reference variables a

Answer 1

In my case I could not use Seq.distinct because I needed to preserve order of list elements. I used solution from http://ocaml.org/learn/tutorials/99problems.html. I think it is quite short

let rec compress = function
    | a :: (b :: _ as t) -> if a = b then compress t else a :: compress t
    | smaller -> smaller