Intro to OCaml
Beyond functional programming in Haskell:
an introduction to OCaml
Michiel Overeem
Center for Software Technology, Universiteit Utrecht
December 21, 2006
Center for Software Technology Michiel Overeem

Intro to OCaml
Functional programming beyond Haskell
We have all learned functional programming in Haskell, but there are
more functional languages like Lisp, Scheme, ML, and Clean.
Why should we even bother to look further than Haskell?
Center for Software Technology Michiel Overeem

Intro to OCaml
Functional programming beyond Haskell
We have all learned functional programming in Haskell, but there are
more functional languages like Lisp, Scheme, ML, and Clean.
Why should we even bother to look further than Haskell?
You want your programs to run faster.
Center for Software Technology Michiel Overeem

Intro to OCaml
Functional programming beyond Haskell
We have all learned functional programming in Haskell, but there are
more functional languages like Lisp, Scheme, ML, and Clean.
Why should we even bother to look further than Haskell?
You want your programs to run faster.
Monads drive you mad (what are they anyway? warm fuzzy
things?).
Center for Software Technology Michiel Overeem

Intro to OCaml
Functional programming beyond Haskell
We have all learned functional programming in Haskell, but there are
more functional languages like Lisp, Scheme, ML, and Clean.
Why should we even bother to look further than Haskell?
You want your programs to run faster.
Monads drive you mad (what are they anyway? warm fuzzy
things?).
You need objects.
Center for Software Technology Michiel Overeem

Intro to OCaml
Functional programming beyond Haskell
We have all learned functional programming in Haskell, but there are
more functional languages like Lisp, Scheme, ML, and Clean.
Why should we even bother to look further than Haskell?
You want your programs to run faster.
Monads drive you mad (what are they anyway? warm fuzzy
things?).
You need objects.
You sometimes need a more powerful module system.
Center for Software Technology Michiel Overeem

Intro to OCaml
OCaml vs Haskell in the ICFP
OCaml performed very well in the previous ICFP contests:
Ocaml Haskell
First place: 2002, 2000, 1999 2006, 2005, 2004, 2001
Second place: 2000, 1998 2004
Third place: 2001 2005, 2000
Lightning division prize: 2003
Judge’s prize: 2004
(Source: caml.inria.fr and ICFP websites)
It look likes OCaml’s days are over...
Center for Software Technology Michiel Overeem

Intro to OCaml
Overview
OCaml facts
1
First steps in OCaml
2
Side-effects
3
The O in OCaml
4
Large applications
5
Some last remarks
6
Conclusion
7
Center for Software Technology Michiel Overeem

Intro to OCaml > OCaml facts
Quick fact sheet
Some facts about Caml (Categorical Abstract Machine Language)
Created in 1987 by INRIA - France’s national research institute for
computer science (Haskell 1.0 is from 1990)
Originated from ML but was intended for in house projects of
INRIA
Short timeline:
Caml (1987) → Caml light (1990) → OCaml (1995)
Currently at version 3.09.3 (3.09 was released in october 2005)
Center for Software Technology Michiel Overeem

Intro to OCaml > First steps in OCaml
Let’s start our OCaml tour
We will start with writing an OCaml version of wc (word count).
This will show us
how to work with input and output, and
how to structure our programs in OCaml.
Let’s begin!
Center for Software Technology Michiel Overeem

Intro to OCaml > First steps in OCaml
Counting words
We want to count chars, words, and lines.
How would we count words in Haskell?
words in Haskell - from the Prelude
words :: String → [String]
words s = case dropWhile Char.isSpace s of
”” → []
s’ → w : words s”
where (w, s”) = break Char.isSpace s’
Center for Software Technology Michiel Overeem

Intro to OCaml > First steps in OCaml
Counting words (2)
How does this translate to OCaml?
words in OCaml
let rec words : string → string list =
fun s → match dropWhile isSpace s with
”” → []
| s’ → let (w, s”) = break isSpace s’
in w :: words s”;;
Center for Software Technology Michiel Overeem

Intro to OCaml > First steps in OCaml
Counting words (2)
How does this translate to OCaml?
words in OCaml
let rec words : string → string list =
fun s → match dropWhile isSpace s with
”” → []
| s’ → let (w, s”) = break isSpace s’
in w :: words s”;;
Center for Software Technology Michiel Overeem

Intro to OCaml > First steps in OCaml
Counting words (2)
How does this translate to OCaml?
words in OCaml
let rec words : string → string list =
fun s → match dropWhile isSpace s with
”” → []
| s’ → let (w, s”) = break isSpace s’
in w :: words s”;;
Center for Software Technology Michiel Overeem

Intro to OCaml > First steps in OCaml
Counting words (2)
How does this translate to OCaml?
words in OCaml
let rec words : string → string list =
fun s → match dropWhile isSpace s with
”” → []
| s’ → let (w, s”) = break isSpace s’
in w :: words s”;;
Center for Software Technology Michiel Overeem

Intro to OCaml > First steps in OCaml
Counting words (2)
How does this translate to OCaml?
words in OCaml
let rec words : string → string list =
fun s → match dropWhile isSpace s with
”” → []
| s’ → let (w, s”) = break isSpace s’
in w :: words s”;;
Center for Software Technology Michiel Overeem

Intro to OCaml > First steps in OCaml
Counting words (3)
We could count the words in OCaml in a different way:
words in OCaml - imperative
let words’ : string → string list =
fun input → let s = ref input in
let words = ref []
in s := dropWhile isSpace !s;
while String.length !s != 0 do
let (w, s’) = break isSpace !s
in words := !words @ [w];
s := s’
done ; !words;;
We can program with loops and references in OCaml, but is it elegant?
Center for Software Technology Michiel Overeem

Intro to OCaml > First steps in OCaml
Counting words (3)
We could count the words in OCaml in a different way:
words in OCaml - imperative
let words’ : string → string list =
fun input → let s = ref input in
let words = ref []
in s := dropWhile isSpace !s;
while String.length !s != 0 do
let (w, s’) = break isSpace !s
in words := !words @ [w];
s := s’
done ; !words;;
We can program with loops and references in OCaml, but is it elegant?
Center for Software Technology Michiel Overeem

Intro to OCaml > First steps in OCaml
Counting words (3)
We could count the words in OCaml in a different way:
words in OCaml - imperative
let words’ : string → string list =
fun input → let s = ref input in
let words = ref []
in s := dropWhile isSpace !s;
while String.length !s != 0 do
let (w, s’) = break isSpace !s
in words := !words @ [w];
s := s’
done ; !words;;
We can program with loops and references in OCaml, but is it elegant?
Center for Software Technology Michiel Overeem

Intro to OCaml > First steps in OCaml
Counting words (3)
We could count the words in OCaml in a different way:
words in OCaml - imperative
let words’ : string → string list =
fun input → let s = ref input in s : string ref
let words = ref []
in s := dropWhile isSpace !s;
while String.length !s != 0 do
let (w, s’) = break isSpace !s
in words := !words @ [w];
s := s’
done ; !words;;
We can program with loops and references in OCaml, but is it elegant?
Center for Software Technology Michiel Overeem

Intro to OCaml > First steps in OCaml
Counting words (3)
We could count the words in OCaml in a different way:
words in OCaml - imperative
let words’ : string → string list =
fun input → let s = ref input in
let words = ref []
in s := dropWhile isSpace !s;
while String.length !s != 0 do
let (w, s’) = break isSpace !s
in words := !words @ [w];
s := s’
done ; !words;;
We can program with loops and references in OCaml, but is it elegant?
Center for Software Technology Michiel Overeem

Intro to OCaml > First steps in OCaml
Counting words (3)
We could count the words in OCaml in a different way:
words in OCaml - imperative
let words’ : string → string list =
fun input → let s = ref input in
let words = ref []
in s := dropWhile isSpace !s;
while String.length !s != 0 do
let (w, s’) = break isSpace !s
in words := !words @ [w];
s := s’
done ; !words;;
We can program with loops and references in OCaml, but is it elegant?
Center for Software Technology Michiel Overeem

Intro to OCaml > First steps in OCaml
Counting words (3)
We could count the words in OCaml in a different way:
words in OCaml - imperative
: string → are only =
let words’Assignments string listallowed on references:
= → ’a → unit
fun input → let s : ’a ref ref input in
( := )
let words = ref []
in s := dropWhile isSpace !s;
while String.length !s != 0 do
let (w, s’) = break isSpace !s
in words := !words @ [w];
s := s’
done ; !words;;
We can program with loops and references in OCaml, but is it elegant?
Center for Software Technology Michiel Overeem

Intro to OCaml > First steps in OCaml
Counting words (3)
We could count the words in OCaml in a different way:
words in OCaml - imperative
let words’ : string → string list =
fun input → let s = ref input in
let words = ref []
in s := dropWhile isSpace !s;
while String.length !s != 0 do
let (w, s’) = break isSpace !s
in words := !words @ [w];
s := s’
done ; !words;;
We can program with loops and references in OCaml, but is it elegant?
Center for Software Technology Michiel Overeem

Intro to OCaml > First steps in OCaml
Counting words (3)
We could count the words in OCaml in a different way:
words in OCaml - imperative
let words’ : string → string list =
fun input → let s = ref input in
let words = ref []
in s := dropWhile isSpace !s;
while String.length !s != 0 do
let (w, s’) = break isSpace !s
in words := !words @ [w];
s := s’
done ; !words;;
We can program with loops and references in OCaml, but is it elegant?
Center for Software Technology Michiel Overeem

Intro to OCaml > First steps in OCaml
Counting words (3)
We could count the words in OCaml in a different way:
words in OCaml - imperative
let words’ : string → string list =
fun input → let s = ref input in
let words = ref []
in s := dropWhile isSpace !s;
while String.length !s != 0 do
let (w, s’) = break isSpace !s
in words := !words @ [w];
s := s’
done ; !words;;
We can program with loops and references in OCaml, but is it elegant?
Center for Software Technology Michiel Overeem

Intro to OCaml > First steps in OCaml
Counting words (3)
We could count the words in OCaml in a different way:
words in OCaml - imperative
let words’ : string → string list =
fun input → let s = ref input in
let words = ref []
in s := dropWhile isSpace !s;
while String.length !s != 0 do
let (w, s’) = break isSpace !s
in words := !words @ [w];
s := s’
done ; !words;;
We can program with loops and references in OCaml, but is it elegant?
Center for Software Technology Michiel Overeem

Intro to OCaml > First steps in OCaml
Counting words (3)
We could count the words in OCaml in a different way:
words in OCaml - imperative
let words’ : string → string list =
fun input → let s = ref input in
let words = ref []
in s := dropWhile isSpace !s;
while String.length !s != 0 do
let (w, s’) = break isSpace !s
in words := !words @ [w];
s := s’
done ; !words;;
We can program with loops and references in OCaml, but is it elegant?
Center for Software Technology Michiel Overeem

Intro to OCaml > First steps in OCaml
Counting words (3)
We could count the words in OCaml in a different way:
words in OCaml - imperative
let words’ : string → string list =
fun input → let s = ref input in
let words = ref []
in s := dropWhile isSpace !s;
while String.length !s != 0 do
let (w, s’) = break isSpace !s
in words := !words @ [w];
s := s’
done ; !words;;
We can program with loops and references in OCaml, but is it elegant?
Center for Software Technology Michiel Overeem

Intro to OCaml > First steps in OCaml
Counting the rest
We can define lines similar to words.
The number of chars can be calculated with
let chars s = String.length s ;;
Center for Software Technology Michiel Overeem

Intro to OCaml > First steps in OCaml
Counting the rest
We can define lines similar to words.
The number of chars can be calculated with
let chars s = String.length s ;; (* We have partial parameterization! *)
Center for Software Technology Michiel Overeem

Intro to OCaml > First steps in OCaml
lazy vs strict
OCaml is strict by default (call-by-value).
OCaml can be lazy, by using the keyword lazy .
laziness in OCaml
let alwaysTwo = 2;;
let divideAndPrint i = let print v = print int (alwaysTwo v)
in print (lazy (i/0));
print (i/0);;
Center for Software Technology Michiel Overeem

Intro to OCaml > First steps in OCaml
lazy vs strict
OCaml is strict by default (call-by-value).
OCaml can be lazy, by using the keyword lazy .
laziness in OCaml
let alwaysTwo = 2;;
let divideAndPrint i = let print v = print int (alwaysTwo v)
in print (lazy (i/0));
print (i/0);;
2Fatal error: exception Division_by_zero
Center for Software Technology Michiel Overeem

Intro to OCaml > Side-effects
Doing some IO
We have defined lines, words and chars. How do we read from a file?
reading a file
let readFile file =
let ichannel = open in file in
let content = ref ”” in
let return = close in ichannel; !content
in try while true do
content := !content ˆ
(input line ichannel) ˆ ”\\n”
done ;
return ()
with End of file → return ();;
Center for Software Technology Michiel Overeem

Intro to OCaml > Side-effects
Doing some IO
We have defined lines, words and chars. How do we read from a file?
reading a file
let readFile file =
let ichannel = open in file in
let content = ref ”” in
let return = close in ichannel; !content
in try while true do
content := !content ˆ
(input line ichannel) ˆ ”\\n”
done ;
return ()
with End of file → return ();;
Center for Software Technology Michiel Overeem

Intro to OCaml > Side-effects
Doing some IO
We have defined lines, words and chars. How do we read from a file?
reading a file
let readFile file =
let ichannel = open in file in
let content = ref ”” in
let return = close in ichannel; !content
in try while true do
content := !content ˆ
(input line ichannel) ˆ ”\\n”
done ;
return ()
with End of file → return ();;
Center for Software Technology Michiel Overeem

Intro to OCaml > Side-effects
Doing some IO
We have defined lines, words and chars. How do we read from a file?
reading a file
let readFile file =
let ichannel = open in file in
let content = ref ”” in
let return = close in ichannel; !content
in try while true do
content := !content ˆ
(input line ichannel) ˆ ”\\n”
done ;
return ()
with End of file → return ();;
Center for Software Technology Michiel Overeem

Intro to OCaml > Side-effects
Doing some IO
We have defined lines, words and chars. How do we read from a file?
reading a file
let readFile file =
let ichannel = open in file in
let content = ref ”” in
let return = close in ichannel; !content
in try while true do
content := !content ˆ
(input line ichannel) ˆ ”\\n”
done ;
return ()
with End of file → return ();;
Center for Software Technology Michiel Overeem

Intro to OCaml > Side-effects
Doing some IO
We have defined lines, words and chars. How do we read from a file?
reading a file
let readFile file =
let ichannel = open in file in
let content = ref ”” in
let return = close in ichannel; !content
in try while true do
content := !content ˆ
(input line ichannel) ˆ ”\\n”
done ;
return ()
with End of file → return ();;
Center for Software Technology Michiel Overeem

Intro to OCaml > Side-effects
Doing some IO
We have defined lines, words and chars. How do we read from a file?
reading a file
let readFile file =
let ichannel = open in file in
let content = ref ”” in
let return = close in ichannel; !content
in try while true do
content := !content ˆ
(input line ichannel) ˆ ”\\n”
done ;
return ()
with End of file → return ();;
Center for Software Technology Michiel Overeem

Intro to OCaml > Side-effects
Doing some IO
We have defined lines, words and chars. How do we read from a file?
reading a file
let readFile file =
let ichannel = open in file in
let content = ref ”” in
let return = close in ichannel; !content
in try while true do
content := !content ˆ
(input line ichannel) ˆ ”\\n”
done ;
return ()
with End of file → return ();;
Center for Software Technology Michiel Overeem

Intro to OCaml > Side-effects
Making our application come together
The building blocks for our first OCaml application are ready
Processing arguments and printing output
let show ls ws cs = print string ( string of int ls ˆ ” ” ˆ
string of int ws ˆ ” ” ˆ
string of int cs ˆ ”\\n”)
let process file = let content = readFile file
in show (List.length (lines content))
(List.length (words content))
(String.length content);;
let = let argslength = Array.length Sys.argv - 1 in
let args = Array.sub Sys.argv 1 argslength
in Array.iter process args
Center for Software Technology Michiel Overeem

Intro to OCaml > Side-effects
Making our application come together
The building blocks for our first OCaml application are ready
Processing arguments and printing output
let show ls ws cs = print string ( string of int ls ˆ ” ” ˆ
string of int ws ˆ ” ” ˆ
string of int cs ˆ ”\\n”)
let process file = let content = readFile file
in show (List.length (lines content))
(List.length (words content))
(String.length content);;
let = let argslength = Array.length Sys.argv - 1 in
let args = Array.sub Sys.argv 1 argslength
in Array.iter process args
Center for Software Technology Michiel Overeem

Intro to OCaml > Side-effects
Making our application come together
The building blocks for our first OCaml application are ready
Processing arguments and printing output
let show ls ws cs = print string ( string of int ls ˆ ” ” ˆ
string of int ws ˆ ” ” ˆ
string of int cs ˆ ”\\n”)
let process file = in acontent =way
Printing let different readFile file
let show in show (List.length (lines content)) ls ws cs;;
cs ws ls = Printf.printf ”%i %i %i\\n”
(List.length (words content))
(String.length content);;
Printf.printf : (’a, out channel, unit) format → ’a
let = let argslength = Array.length Sys.argv - 1 in
let args = Array.sub Sys.argv 1 argslength
in Array.iter process args
Center for Software Technology Michiel Overeem

Intro to OCaml > Side-effects
Making our application come together
The building blocks for our first OCaml application are ready
Processing arguments and printing output
let show ls ws cs = print string ( string of int ls ˆ ” ” ˆ
string of int ws ˆ ” ” ˆ
string of int cs ˆ ”\\n”)
let process file = let content = readFile file
in show (List.length (lines content))
(List.length (words content))
(String.length content);;
let = let argslength = Array.length Sys.argv - 1 in
let args = Array.sub Sys.argv 1 argslength
in Array.iter process args
Center for Software Technology Michiel Overeem

Intro to OCaml > Side-effects
Making our application come together
The building blocks for our first OCaml application are ready
Processing arguments and printing output
let show ls ws cs = print string ( string of int ls ˆ ” ” ˆ
string of int ws ˆ ” ” ˆ
string of int cs ˆ ”\\n”)
let process file = let content = readFile file
in show (List.length (lines content))
(List.length (words content))
(String.length content);;
let = let argslength = Array.length Sys.argv - 1 in
let args = Array.sub Sys.argv 1 argslength
in Array.iter process args
Center for Software Technology Michiel Overeem

Intro to OCaml > Side-effects
Making our application come together
The building blocks for our first OCaml application are ready
Processing arguments and printing output
let show ls ws cs = print string ( string of int ls ˆ ” ” ˆ
string of int ws ˆ ” ” ˆ
string of int cs ˆ ”\\n”)
let process file = let content = readFile file
in show (List.length (lines content))
(List.length (words content))
(String.length content);;
let = let argslength = Array.length Sys.argv - 1 in
let args = Array.sub Sys.argv 1 argslength
in Array.iter process args
Center for Software Technology Michiel Overeem

Intro to OCaml > Side-effects
Making our application come together
The building blocks for our first OCaml application are ready
Processing arguments and printing output
Arrays in Ocaml
let show ls ws OCaml are string ( string of int destructive updates.
Arrays in cs = print mutable, they have ls ˆ ” ” ˆ
string of int ws ˆ ” ” ˆ
let show content = let statsstring of int cs ˆ ”\\n”)
= Array.make 3 1
in stats.(0) ← List.length (lines content);
let process file = let contentstats.(1) ← file
= readFile List.length (words content);
in show (List.length ← String.length content;
stats.(2) (lines content))
(List.length ( fun → print
Array.iter (wordsx content))int x;
(String.length print string ” ”) stats
content);;
let = let argslength = Array.length Sys.argv - 1 in
let args = Array.sub Sys.argv 1 argslength
in Array.iter process args
Center for Software Technology Michiel Overeem

Intro to OCaml > Side-effects
Making our application come together
The building blocks for our first OCaml application are ready
Processing arguments and printing output
Arrays in Ocaml
let show ls ws OCaml are string ( string of int destructive updates.
Arrays in cs = print mutable, they have ls ˆ ” ” ˆ
string of int ws ˆ ” ” ˆ
let show content = let statsstring of int cs ˆ ”\\n”)
= Array.make 3 1
in stats.(0) ← List.length (lines content);
let process file = let contentstats.(1) ← file
= readFile List.length (words content);
in show (List.length ← String.length content;
stats.(2) (lines content))
(List.length ( fun → print
Array.iter (wordsx content))int x;
(String.length print string ” ”) stats
content);;
let = let argslength = Array.length Sys.argv - 1 in
let args = Array.sub Sys.argv 1 argslength
in Array.iter process args
Center for Software Technology Michiel Overeem

Intro to OCaml > Side-effects
Making our application come together
The building blocks for our first OCaml application are ready
Processing arguments and printing output
Arrays in Ocaml
let show ls ws OCaml are string ( string of int destructive updates.
Arrays in cs = print mutable, they have ls ˆ ” ” ˆ
string of int ws ˆ ” ” ˆ
let show content = let statsstring of int cs ˆ ”\\n”)
= Array.make 3 1
in stats.(0) ← List.length (lines content);
let process file = let contentstats.(1) ← file
= readFile List.length (words content);
in show (List.length ← String.length content;
stats.(2) (lines content))
(List.length ( fun → print
Array.iter (wordsx content))int x;
(String.length print string ” ”) stats
content);;
let = let argslength = Array.length Sys.argv - 1 in
let args = Array.sub Sys.argv 1 argslength
in Array.iter process args
Center for Software Technology Michiel Overeem

Intro to OCaml > Side-effects
Making our application come together
The building blocks for our first OCaml application are ready
Processing arguments and printing output
Arrays in Ocaml
let show ls ws OCaml are string ( string of int destructive updates.
Arrays in cs = print mutable, they have ls ˆ ” ” ˆ
string of int ws ˆ ” ” ˆ
let show content = let statsstring of int cs ˆ ”\\n”)
= Array.make 3 1
in stats.(0) ← List.length (lines content);
let process file = let contentstats.(1) ← file
= readFile List.length (words content);
in show (List.length ← String.length content;
stats.(2) (lines content))
Array.iter ( fun → print
(List.length (wordsx content))int x;
(String.length print string ” ”) stats
content);;
let = let argslength = Array.length Sys.argv - 1 in
let args = Array.sub Sys.argv 1 argslength
in Array.iter process args
Center for Software Technology Michiel Overeem

Intro to OCaml > Side-effects
Making our application come together
The building blocks for our first OCaml application are ready
Processing arguments and printing output
let show ls ws cs = print string ( string of int ls ˆ ” ” ˆ
string of int ws ˆ ” ” ˆ
string of int cs ˆ ”\\n”)
let process file = let content = readFile file
in show (List.length (lines content))
(List.length (words content))
(String.length content);;
let = let argslength = Array.length Sys.argv - 1 in
let args = Array.sub Sys.argv 1 argslength
in Array.iter process args
Center for Software Technology Michiel Overeem

Intro to OCaml > Side-effects
Making our application come together
The building blocks for our first OCaml application are ready
Processing arguments and printing output
let show ls ws cs = print string ( string of int ls ˆ ” ” ˆ
string of int ws ˆ ” ” ˆ
string of int cs ˆ ”\\n”)
Processing our arguments (2)
let process file = 1let content = readFile file- 1 do
for i to Array.length Sys.argv
in show (List.length (lines content))
process Sys.argv.(i)
(List.length (words content))
done ;;
(String.length content);;
let = let argslength = Array.length Sys.argv - 1 in
let args = Array.sub Sys.argv 1 argslength
in Array.iter process args
Center for Software Technology Michiel Overeem

Intro to OCaml > The O in OCaml
Counting words in object-oriented style
The O stands for Objective: we can use classes and objects in OCaml.
class wcCounter file =
let content = readFile file in
object (self)
method private words = . . .
method show = . . .
end ;;
for i = 1 to Array.length Sys.argv - 1 do
let counter = new wcCounter Sys.argv.(i)
in counter#show
done ;;
Center for Software Technology Michiel Overeem

Intro to OCaml > The O in OCaml
Counting words in object-oriented style
The O stands for Objective: we can use classes and objects in OCaml.
class wcCounter file =
let content = readFile file in
object (self)
method private words = . . .
method show = . . .
end ;;
for i = 1 to Array.length Sys.argv - 1 do
let counter = new wcCounter Sys.argv.(i)
in counter#show
done ;;
Center for Software Technology Michiel Overeem

Intro to OCaml > The O in OCaml
Counting words in object-oriented style
The O stands for Objective: we can use classes and objects in OCaml.
class wcCounter file =
let content = readFile file in
object (self)
method private words = . . .
method show = . . .
end ;;
for i = 1 to Array.length Sys.argv - 1 do
let counter = new wcCounter Sys.argv.(i)
in counter#show
done ;;
Center for Software Technology Michiel Overeem

Intro to OCaml > The O in OCaml
Counting words in object-oriented style
The O stands for Objective: we can use classes and objects in OCaml.
class wcCounter file =
let content = readFile file in
object (self)
method private words = . . .
method show = . . .
end ;;
for i = 1 to Array.length Sys.argv - 1 do
let counter = new wcCounter Sys.argv.(i)
in counter#show
done ;;
Center for Software Technology Michiel Overeem

Intro to OCaml > The O in OCaml
Counting words in object-oriented style
The O stands for Objective: we can use classes and objects in OCaml.
class wcCounter file =
let content = readFile file in
object (self)
method private words = . . .
method show = . . .
end ;;
for i = 1 to Array.length Sys.argv - 1 do
let counter = new wcCounter Sys.argv.(i)
in counter#show
done ;;
Center for Software Technology Michiel Overeem

Intro to OCaml > The O in OCaml
Counting words in object-oriented style
The O stands for Objective: we can use classes and objects in OCaml.
class wcCounter file =
let content = readFile file in
object (self)
method private words = . . .
method show = . . .
end ;;
for i = 1 to Array.length Sys.argv - 1 do
let counter = new wcCounter Sys.argv.(i)
in counter#show
done ;;
Center for Software Technology Michiel Overeem

Intro to OCaml > The O in OCaml
Counting words in object-oriented style
The O stands for Objective: we can use classes and objects in OCaml.
class wcCounter file =
let content = readFile file in
object (self)
method private words = . . .
method show = . . .
end ;;
for i = 1 to Array.length Sys.argv - 1 do
let counter = new wcCounter Sys.argv.(i)
in counter#show
done ;;
Center for Software Technology Michiel Overeem

Intro to OCaml > The O in OCaml
Counting words in object-oriented style
The O stands for Objective: we can use classes and objects in OCaml.
class wcCounter file =
let content = readFile file in
object (self)
method private words = . . .
method show = . . .
end ;;
for i = 1 to Array.length Sys.argv - 1 do
let counter = new wcCounter Sys.argv.(i)
in counter#show
done ;;
Center for Software Technology Michiel Overeem

Intro to OCaml > The O in OCaml
Objects vs Datatypes
Object features:
inheritance
encapsulation (private members)
constructor function (for initialization)
Datatype features:
pattern matching
multiple type constructors
Center for Software Technology Michiel Overeem

Intro to OCaml > Large applications
Modularize your application
Until now we have only seen a small application. How do we structure
our larger applications?
module Set =
struct
type element = string
type set = element list
let rec member x s =
match s with
...
end ;;
Center for Software Technology Michiel Overeem

Intro to OCaml > Large applications
Modularize your application
Until now we have only seen a small application. How do we structure
our larger applications?
module Set =
struct
type element = string
type set = element list
let rec member x s =
match s with
...
end ;;
Center for Software Technology Michiel Overeem

Intro to OCaml > Large applications
Modularize your application
Until now we have only seen a small application. How do we structure
our larger applications?
module Set =
struct
type element = string
type set = element list
let rec member x s =
match s with
...
end ;;
Center for Software Technology Michiel Overeem

Intro to OCaml > Large applications
Modularize your application
Until now we have only seen a small application. How do we structure
our larger applications?
module Set =
struct
type element = string
type set = element list
let rec member x s =
match s with
...
end ;;
Center for Software Technology Michiel Overeem

Intro to OCaml > Large applications
Parameterize your module
Now we have a Set module, but with a fixed type and comparison
function. We want this to be parameterized!
Center for Software Technology Michiel Overeem

Intro to OCaml > Large applications
Parameterize your module
Now we have a Set module, but with a fixed type and comparison
function. We want this to be parameterized!
We first define a module type for comparison.
type comparison = LT | GT | EQ;;
module type OrderedType =
sig
type t
val compare : t → t → comparison
end ;;
Center for Software Technology Michiel Overeem

Intro to OCaml > Large applications
Parameterize your module (2)
We can now define a default ordering on strings:
module OrderedString : OrderedType =
struct
type t = string
let compare x y = . . .
end ;;
Center for Software Technology Michiel Overeem

Intro to OCaml > Large applications
Parameterize your module (2)
We can now define a default ordering on strings:
module OrderedString : OrderedType =
struct
type t = string
let compare x y = . . .
end ;;
But we might want a second, case insensitive, ordering:
module CIOrderedString : OrderedType =
struct
type t = string
let compare x y =
let x’ = String.uppercase x in
let . . .
Center for Software Technology Michiel Overeem

Intro to OCaml > Large applications
Parameterize your module (3)
How do we give a specific comparison to the Set module?
module Set (Ord : OrderedType) =
struct
type element = Ord.t
type set = element list
...
let rec member x s in
match s with
→ false
[]
| hd::tl → match Ord.compare x hd with
...
end ;;
Center for Software Technology Michiel Overeem

Intro to OCaml > Large applications
Parameterize your module (3)
How do we give a specific comparison to the Set module?
module Set (Ord : OrderedType) =
struct
type element = Ord.t
type set = element list
...
let rec member x s in
match s with
→ false
[]
| hd::tl → match Ord.compare x hd with
...
end ;;
Center for Software Technology Michiel Overeem

Intro to OCaml > Large applications
Parameterize your module (3)
How do we give a specific comparison to the Set module?
module Set (Ord : OrderedType) =
struct
type element = Ord.t
type set = element list
...
let rec member x s in
match s with
→ false
[]
| hd::tl → match Ord.compare x hd with
...
end ;;
Center for Software Technology Michiel Overeem

Intro to OCaml > Large applications
Parameterize your module (4)
Now we can define our specific modules:
module StringSet = Set (OrderedString);;
module CIStringSet = Set (CIOrderedString);;
And we could parameterize even further . . .
Center for Software Technology Michiel Overeem

Intro to OCaml > Large applications
Parameterize your module (4)
Now we can define our specific modules:
module StringSet = Set (OrderedString);;
module CIStringSet = Set (CIOrderedString);;
And we could parameterize even further . . .
The OCaml modules are not first class, because they are units of
compilation.
They do offer something different from Haskell’s type classes: we
can define different comparisons on the same type in the same
scope.
Center for Software Technology Michiel Overeem

Intro to OCaml > Some last remarks
More features
We have seen some of the most exciting features of OCaml, but there
is much more:
Records
There are bindings to GTK+ and wxWidgets
Syntax extensions for defining DSL’s
Lot’s of (standard) libraries
Center for Software Technology Michiel Overeem

Intro to OCaml > Some last remarks
Finally, the performance
People tell that OCaml is fast, way faster than Haskell.
(see The great computer language shootout)
The reason for OCaml’s excellent performance:
strict evaluation
the compiler
mutable datastructures
Or as some would say trading elegance for efficiency.
Center for Software Technology Michiel Overeem

Intro to OCaml > Some last remarks
Current research on OCaml
AtomCaml This project gives the ability to make execution of
code atomic.
Aspectual Caml Brings aspect-oriented features to the OCaml
langague.
F# An OCaml-like language on the .NET platform.
Center for Software Technology Michiel Overeem

Intro to OCaml > Conclusion
My thoughts
What I like about OCaml:
it’s functional and object-oriented
the module system is powerful
it’s fast without weird hacks (they say)
Center for Software Technology Michiel Overeem

Intro to OCaml > Conclusion
My thoughts
What I like about OCaml:
it’s functional and object-oriented
the module system is powerful
it’s fast without weird hacks (they say)
What I do not like
it’s functional and object-oriented
verbose syntax (top level let and ; ; )
sometimes efficiency over elegance
Center for Software Technology Michiel Overeem