for some odd reason (well... maybe not odd, but one i can't figure out), the return type of this function is being inferred as unit, despite the fact that the only non-recursive return occurs inside the first if statement, with a value that's an int. any ideas? also, i'll take any overall recommendations on cleaning this mess up a bit.

/// Parses a variable definition
let rec parse_var (filter_match: Match) (upto: int) var =
if not (filter_match.Success) then
upto

let fast_call = fun v -> parse_var (filter_match.NextMatch()) (filter_match.Index + filter_match.Length) v
if not (upto = filter_match.Index) then
failwith (sprintf "Could not parse some characters %s|%s|%s" _token.[..upto] _token.[upto..filter_match.Index] _token.[filter_match.Index..])

match var with
| None ->
let i18n_constant = filter_match.Groups.["i18n_constant"]
if not (i18n_constant = null) then
if (i18n_constant.Value = "") then
fast_call (Some "\"\"")
else
fast_call (Some <| flatten i18n_constant)

let constant = filter_match.Groups.["constant"]
if not (constant = null) then
fast_call (Some <| flatten constant)
let _var = filter_match.Groups.["var"]
if _var = null then
failwith (sprintf "Could not find variable at start of %s" token)
elif (_var.Value.IndexOf(Constants.VARIABLE_ATTRIBUTE_SEPARATOR + "_") > -1) || _var.Value.[0] = '_' then
failwith (sprintf "Variables and attributes may not begin with underscores: '%s'" _var.Value)

fast_call (Some _var.Value)
| Some s->
let filter_name = filter_match.Groups.["filter_name"]
let arg = find_arg filter_match.Groups [(false, "i18n_arg"); (false, "constant_arg"); (true, "var_arg")]
filters := !filters @ [(_parser.FindFilter filter_name.Value, arg)]
fast_call var