epicours/Algo/Séminaire/Chapter 4 - A bit of imperative.md

0.1. Print

If we want to print something in CAML, we have to use this structure

# print_string "Hello World!";;
Hello! - : unit=()

# print_int ;;
-: int -> unit = <fun>

(*expression*)
# print_[type] [things to print];;
[things to print] -: unit=()

Difference between compiler and interpreter for print

flowchart LR

A[CAML] -- compile --> B[ ] -- exec --> C[standard output] & D[standard error] ~~~ E(on your terminal)

flowchart LR

A[CAML] -- interpreter --> B[standard error] & C[standard output] & D[CAML answer] ~~~ E(in the interpreter interface)

To print something and create a new line for the CAML evaluation

# print_endline "toto";;
toto
-: unit = ()

To just print a newline

# print_newline();;
-: unit = ()

(* example *)
# print_newline(print_int 54);;
54
-: unit = ()

0.2. Sequence of prints

To print two things on the same line we have to use this structure

# print_string "The answer is: "; print_int 42;;
The answer is: 42 -: unit = ()

# 3*2*7; print_string "The answer is : ";;
The answer is -: unit = () 
Warning 10 [non-unit-statement]: this expression should have type unit.

# print_string "The answer is: "; 3*2*7;;
The answer is: -:int = 42

0.3. Print in a function

# let print_even n = 
	if n mod 2 = 0 then
		print_int n;;
	(*Caml will automaticaly add the else with a empty value ()*)
val print_even: int -> unit = <fun>

# print_even 4;;
4 -: unit = ()

# print_even 7;;
-: unit = ()

# let ret_even n =
	if n mod 2 = 0 then
		n;;
Error: should have int type (*because of the hidden else*)

# let print_even n = 
	if n mod 2 = 0 then
		begin
			print_int n ;
			print_newline()
		end;; (*begin and end used to execute more than 1 function into a if*)
val print_even : int -> unit = <fun>

# print_even 4;;
4
-: unit = ()