OCaml
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OCaml is a functional programming language in the ML family, an extension of the Caml language with objectoriented constructs.
This page aims to cover some of its differences from Haskell.
Conceptual differences
OCaml is strict by default, although it has some facility for introducing laziness.
OCaml's let is nonrecursive by default, but has the form let rec for defining recursive functions.
OCaml is impure: although it makes heavy use of immutable data, it also has mutable references and arrays available, and IO is performed by ordinary functions.
Syntactic dictionary
Haskell  OCaml  Comments  
Anonymous functions 
\x y > ... 
fun x y > ... 

Multiple assignments 
let x = 4 y = 5 in ... 
let x = 4 and y = 5 in ... 

Types 
Int, Bool, (Double, Char), a 
int, bool, float * char, 'a 
float is doubleprecision 
Type signatures 
const :: a > b > a 
const : 'a > 'b > 'a 
Signatures usually omitted in OCaml implementations, may be provided separately in interface files 
Type declarations 
data A = B Int  C Char Bool x = B 3 y = C 'a' True 
type a = B of int  C of char * bool let x = B 3 and y = C ('a', true) 

Parametrised types 
data DList a = MkDList ([a] > [a]) data Either a b = Left a  Right b 
type 'a dlist = MkDList of ('a list > 'a list) type ('a, 'b) either = Left of 'a  Right of 'b  
Pattern matching 
case x of B x  x > 0 > ...  otherwise > ... C a b > ... case Left () of Left x > x Right x > x 
match x with B x when x > 0 > ...  B x > ...  C (a, b) > ... match Left () with Left x  Right x > x 