Difference between revisions of "OCaml"

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(New page: '''OCaml''' is a functional programming language in the ML family, an extension of the Caml language with object-oriented constructs. This page aims to cover some of its differences from ...)
 
(clarifications on comments)
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This page aims to cover some of its differences from Haskell.
  
This page aims to cover some of its differences from Haskell.
   
−
== Syntactic differences ==
 +
== Conceptual differences ==
  +
  +
OCaml is strict by default, although it has some facility for introducing laziness.
  +
  ⚫
OCaml's <tt>let</tt> is non-recursive by default, but has the form <tt>let rec</tt> 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 ==
   
 
{| class="wikitable"
  
{| class="wikitable"
  +
|
−
| Language
  
−
| Haskell
 +
| '''Haskell'''
−
| OCaml
 +
| '''OCaml'''
−
| Comments
 +
| '''Comments'''
 
|-
  
|-
 
| Anonymous functions
  
| Anonymous functions
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|
  
|
 
int, bool, float * char, 'a
  
int, bool, float * char, 'a
−
| <tt>float</tt> is a double type
 +
| <tt>float</tt> is double-precision
 
|-
  
|-
 
| Type signatures
  
| Type signatures
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|
  
|
 
const : 'a -> 'b -> 'a
  
const : 'a -> 'b -> 'a
−
| Signatures usually omitted in OCaml
 +
| Signatures usually omitted in OCaml implementations, may be provided separately in interface files
 
|-
  
|-
 
| Type declarations
  
| Type declarations
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and y = C ('a', true)
  
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
  
| Pattern matching
 
|
  
|
 
case x of
  
case x of
−
A x -> ...
 +
B x
  +
<nowiki>| x > 0 -> ...
  +
|</nowiki> otherwise -> ...
 
C a b -> ...
  
C a b -> ...
  +
  +
case Left () of
  +
Left x -> x
  +
Right x -> x
 
|
  
|
 
match x with
  
match x with
−
B x -> ...
 +
B x when x > 0 -> ...
−
C (a, b) -> ...
 +
<nowiki>| B x -> ...
  +
|</nowiki> C (a, b) -> ...
  +
  +
match Left () with
  +
Left x <nowiki>|</nowiki> Right x -> x
  +
|
 
|}
  
|}
−  
−
== Conceptual differences ==
  
−  
⚫
OCaml's <tt>let</tt> is non-recursive and strict by default, but has keywords <tt>rec</tt> (as in <tt>let rec</tt>) and <tt>lazy</tt> to introduce the Haskell behaviour.
  
−  
⚫
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.
  

Latest revision as of 16:34, 15 May 2023

OCaml is a functional programming language in the ML family, an extension of the Caml language with object-oriented 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 non-recursive 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 double-precision
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
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