Match with empty sequence
The suggestion that ildjarn gave in the comments is a good one: if you feel that using match
would create more readable code, then make an active pattern to check for empty seqs:
let (|EmptySeq|_|) a = if Seq.isEmpty a then Some () else None
let s0 = Seq.empty<int>
match s0 with
| EmptySeq -> "empty"
| _ -> "not empty"
Run that in F# interactive, and the result will be "empty"
.
You can use a when
guard to further qualify the case:
match span with
| sequence when Seq.isEmpty sequence -> String.Empty
| span -> span
|> Seq.collect (fun (n: HtmlNode) ->
n.Descendants()
|> Seq.filter (fun m -> m.HasName("a")))
|> Seq.last
|> fun n -> n.AttributeValue("href")
ildjarn is correct in that in this case, an if...then...else
may be the more readable alternative, though.