Pattern Matching in OCaml

Question 1

To access the various components of data structures, OCaml uses this powerful feature to divide the process into various branches or cases

Answer 1

Pattern matching

let rec sum lst =
match lst with
| [] -> 0
| h::t -> h + sum t ;;

Question 2

The underscore symbol that matches anything

Answer 2

Wildcard

let xor p =
match p with
| (true, false) -> true
| (false, true) -> true
| _ -> false ;;

Question 3

Recursive function that does not perform any computation after the recursive call returns, and immediately returns to its caller the value of its recursive call

Answer 3

Tail recursion

Question 4

Recursion leads to a call stack. Instead of growing this, the caller’s stack frame is simply replaced with that of the called function. What is this called

Answer 4

Tail call optimization

Question 5

What is the output?

let f x =
match x with
“foo” -> “it is foo”
| “bar” -> “bar is the one”
| “zap” -> “totally different”
| _ -> “our default: “ ^ x
;;
val f : string -> string = <fun>
# f "hello";;
- : string = ?????
# f "bar";;
- : string = ?????</fun>

Answer 5

“our default: hello”

“bar is the one”

Question 6

What is the output?

# let rec mem x list =
match list with 
  [] -> false
| hd::tl -> hd = x || mem x tl
  ;;
val mem : 'a -> 'a list -> bool = <fun>
# mem 3 [1;2;3;4;5];;
- : bool = ?????
# mem 12 [1;2;3;4;5];;
- : bool = ?????

Answer 6

true

false