(* alternative syntax for parametric types *)
let l1 : int list = [1;2]
let l2 : List = [1;2]
(* Immutable maps *)
let m = Map.empty
let m1 = Map.add "a" 1 m
let m2 = Map.add "b" 2 m1
let m4 = Map.empty |> Map.add "a" 1 |> Map.add "b" 3 |> Map.add "c" 0
let m5 = Map.remove "b" m4
m4
Map.find "b" m4
Map.find "b" m5
Map.tryFind "b" m5
Map.tryFind "b" m4
(* Option Types *)
type 'a option = None | Some of 'a
let o1 = Some 0.4
let o2 = Some "aaa"
let o3 = None
let l = []
let f x =
match x with
| Some _ -> "I got something"
| None -> "I got nothing"
f (Some 5)
f None
let g (x: int option) =
match x with
| Some n -> "I got " + string n
| None -> "I got nothing"
g (Some 5)
let rec lookup env x =
match env with
| [] -> failwith (x + " not found")
| (y, v) :: t -> if x = y then v else lookup t x
let rec lookup env x =
match env with
| [] -> None
| (y, v) :: t -> if x = y then Some v else lookup t x
let e = [("a", 1); ("b", 4)]
lookup e "a"
lookup e "aa"
(* expression sequences *)
// ; is an infix binary operator that takes two expressions of any type,
// evaluates them in order and returns the value of the second
3 ; 5 // evaluates to 5
"abc" ; (1+4) // also evaluates to 5
// all these evaluate to 5
3; 4; 5
(3; 4); 5
3; (4; 5)
let a = 3;4;5
// assignments are expressions that have value ()
// the value is not interesting, we evaluate assignment only for
// their side effect (changing the value of a mutable variable)
let mutable a = 1
let mutable b = 2
let x = a <- 3
x
a
// ; is interesting only with expression that have *side effects*
// such as assignments
// assigns 4 to a, returns 5
a <- 4; 5
// assigns 7 to a, assigns 8 to b, returns ()
a <- 7; b <- 8
a
// ; can be replaced by the end-of-line character
(a <- 7
b <- 8
)
a
b
// ; can be replaced by end of line char
let f x =
if x > 0 then (
a <- 10
b <- 11
) else ()
f 4
a
b
// ; is often used in while loops
while (z > 0) do (printfn "%i\n" z; z <- z - 1)
while (z > 0) do (
printfn "%i\n" z;
z <- z - 1
)
// semicolon separator can be replaced by a new line character
// and indentation
while (z > 0) do
printfn "%i\n" z
z <- z - 1