fs-pattern-matching-stuff.fs

type BST<`T> =
    | Empty // handle empty case
    | Node of `T * BST<`T> * BST<`T> // Node with a value and two subtrees
  

let foo tree =
    match tree with
    | Empty -> // do something with empty case
    | Node(value, left, right) -> // 'value' is the value, 'left' and 'right' are the subtrees

module Parsing =
    open System
    
    let tryParseHelper f s =
        match (f s) with
        | true, v -> Some v
        | false, _ -> None
    
    let tryParseDateTime s = tryParseHelper DateTime.Parse s
    // add another if you want

open Parsing

let res = tryParseDateTime "2015-09-28"

// need to pattern match to actually get value, thus account for parse failure at compile time
match res with
| Some v -> // something with the value
| None -> // handle parse error


open System.Text.RegularExpressions
// active pattern, check this shit out  
let (|Matches|_|) str pattern =
    let mt = let mat = Regex.Match(str, pattern, RegexOptions.Compiled ||| RegexOptions.IgnoreCase)
    if mt.Success then Some(str) else None
    
let fooRegex str pattern =
    match str with
    | Matches pattern -> // yay, we got a regex match
    | _ -> // no match