NonEmpty Uncons pattern

[cmorley191]

Add an uncons pattern so I can do something like

let myThings = [1; 2; 3; 4; 5]
match myThings with
| Empty -> failwith "oh"
| NotEmpty (Uncons (head, tail)) -> printf "%i, then the rest: %A" head tail

outputs "1, then the rest: [2; 3; 4; 5]"

[ntwilson]

this is a cool idea. Right now you can do the workaround:

let myThings = [1 .. 5]
match myThings with
| [] -> failwith "oh"
| head :: tail -> printf "%i, then the rest: %A" head tail

and there's a SeqOneOrMore matcher that you can use for generic Seqs if it's not a list,
but this doesn't let you do something like | NotEmpty ((Uncons (head, tail)) as nonEmptyList) -> ..., and the matcher may not be as wellknown as the NonEmpty stuff.