[F#] Ido dictionary converter

Convert.fsx

// https://github.com/kyegupov/ido_web_dictionary

// https://gist.github.com/7shi/de072cd867f3899aa285bc9343110bff
#load "XmlParser.fsx"

open System
open System.IO
open System.Text
open XmlParser

let dir = "ido_web_dictionary/service_data/dictionaries_by_letter"

let convert (dict:string) =
    let dir = Path.Combine(dir, dict)
    use sw = new StreamWriter(dict + ".txt")
    let files =
        Directory.GetFiles(dir)
        |> Seq.filter (Path.GetExtension >> (=) ".txt")
        |> Seq.sortBy Path.GetFileNameWithoutExtension
    for file in files do
        let mutable src = ""
        let f() =
            if src = "" then () else
            use xp = new XmlParser(src)
            while xp.Read() do
                sw.Write(fromEntity xp.Text)
            sw.WriteLine()
        for line in File.ReadAllLines file do
            if line = "" then
                f()
                src <- ""
            elif src = "" then
                src <- line
            else
                src <- src + " " + line
        f()

convert "en-io"
convert "io-en"