epicours/Algo/Séminaire/Chapter 1 - CAML basics.md

CAML is a categorical abstract machine language. It is strongly typed. It was created by INRIA in 1984.

1.1. General idea

It's a simple language to write.

# 1+2 ;;

• # is the prompt (we don't have to write it)
• 1 + 2 is the program
• ;; is the end of the line

_: int=3 (*That a Caml answer to the previous program*)

# 1+2.2;; (*That an error*)

# 1. +. 2.2;; (*This is good*)

1.2. CAML interaction

# 1;; (*He can be a simple expression*)
_: int=1

# "Hello World";; (*He can be a string*)
_:string = "Hello World"

The general form is :

# expr ;;
_: type of the evaluation = result  of the evaluation

1.3. Definitions

Global definitions

# let x=1+2;;
val x:int = 3 (*our current env is x -> 3*)

# let y=x/2;;
val y:int = 1 (*our current env is x -> 3 ; y -> 1*)

# let x = 2
val x : int = 2

# x;;
_: int = 2

# let name = expr;;
val name: type of evaluation

Local definitions

# let r = 1. in let pi = 3.14 in 2*pi*r;;
- : float = 6.28

# let x = 10 in y = 2*x in x+y;;
- : float = 30

# x;;
- : int =2 (*see global definition section*)

# pi;;
error: unbound value pi

when there is the keyword lenand in that create a local definition. A local definition is something that only exist in our expression and then it disappear. You can define a local definition into a variable : let x = let r = 1. in let pi = 3.14 in 2*pi*r;; (for example)

Multiple definitions

# let r = 1. and pi = 3.14 in 2 *. pi *. r;; (*local version*)
- : float = 6.28 

# let x = 1.2 and y = "Hello";;
val x: float = 1.2 (*our current env is x -> 3 ; y -> 1 ; x -> 1.2 *)
val y: string = "Hello" (*our current env is x -> 3 ; y -> 1 ; x -> 1.2 ; y -> "Hello"*)
# let x = 2 and y = x + 1 in y + 2;;
Error (*because x is 1.2 in our current evaluation*)

⚠️ We have only one let and one in for the multiple definitions methods

1.4 Basic types

• Integer: int

  • Compatible operator : + ; - ; * ; / ; mod
  • Same operator priority than in mathematics

    # 2+3*2;;
    _: int = 8
    
    # (2+3)*3;;
    _: int = 10
    
    # max_int 1 073 741 823
    _: int = 2^30-1
    
    # max_int -1 073 741 824
    _: int = -2^30
    

• Float: float

  • Compatible operator : -. ; +. ; * . ; /.

• Booleans: bool

  • Can be trueor false

  # let x = 2 and y = 1 in x/y > 1;;
  _: bool = true
  
  # let x = 2 and y = 0 in x/y > 1;;
  Exception: Division by zero
  
  # let x = 2 and y = 0 in y<>0 && x/y> 1;;
  _: bool = false
  

• Char: char

  • 8 bits -> extended ASCII table

# 'a'= 'A';;
_: bool = false

# 'a'
- : char = 'a'

• String: string

# "ab" < "abc" ;;
_: bool = true (*because O chars -> 2^24 - 6 chars*)

# "Hello" ^" World"
_: string = "Hello World"

# "abc".[1]
_: char = "b"

⚠️ Les minuscules passent avant les majuscules

Comparaison

|Mathematics|$=$|$\not=$|$<$|$>$|$\eqslantgtr$|$\eqslantless$| |:----:|:----:|:----:|:----:|:----:|:----:| |CAML|=|<>|<|>|<=|>=|

CAML	Maths	English
not	\neg	negation
&&	\land	and
// (vertical bar)	\lor	or (inclusive)