epicours/Algo/Séminaire/Chapter 5 - Recursivity.md

5.1. Simple functions

To create a recursive function we have to use this structure

(*normal function*)
# let f = expr -> 1) evaluate expr ; 2) create & link f to the result

(*recursiv function*)
# let rec f = expr -> 1) create f ; 2) evaluate expr ; 3) link f to the result

Exmple with factorial function

# let rec fact = function 
	| 0 -> 1
	| n -> n * fact(n-1)

# fact 4;;
-: int = 24

⚠️ CAML have a call stack limite (it will block with stack overflow if the limit is reach)

Basic expression

let rec f params = 
	if stop condition then 
		stop expression
	else
		recursive expression 

To write a recurvise function we need two things

1. There always is a stop case
2. The parameters of a recursive call are different then its parent call, and go towards the stop condition

5.2. Down

# let rec countdown n = 
	if n < 0 then
		()
	else
		begin
			print_int n ;
			print_newline();
			countdown(n-1);
		end;;
val countdown = int -> unit = ()

# countdown 3;;
3
2
1
- : unit = ()