epicours/Algo/Séminaire/Chapter 3 - Case analysis.md

3.1. The alternative

The if structure

if cond then expr1 else expr2

⚠️ expr1 and expr2 have to be the same type. cond is a bool

For exemple

# if 1<2 then "higher" else "lower" ;;
-: string = "higher"

Exercise : absolute program

# let abs(x) = 
	if x>0 then x
	else -x ;;;
val abs : int -> int <fun>

3.2. Exceptions

Division by 0:

# 1/0
Exception : Division by zero

Failwith:

Failwith is a function that take a string argument (the reason) and return the error. That way, we can raise an error into our code

# failwith;;
-: string -> a = <fun>

# failwith "oops";;
Exception : Failwith "oops"

invalid_arg:

Invalid_arg is a function that take a string argument (the reason) and return the error. That way, we can raison an error about an argument

# invalid_arg "oops";
Exception: Invalid_argument "oops"

(*example*)
# let div a b = 
	if b = 0 then invalid_arg("div: b = 0")
	else a/b ;;;
val div int -> int -> int = <fun>