JavaScript
Haskell
2008-01-24
UJIHISA, Tatsuhiro

who's this?
• ujihisa
• Osaka Univ. M2
• Fuzzy Rough Sets
• nayutaya - http://www.nayutaya.co.jp
• LiveCoding, ldev, Haskell, On Lisp...

from js to hs

Ruby natural class-based OO
prototype-based
JavaScript
OO, functional
Haskell simple functional

simplicity
• process serially
• assignment
• loop
• implicit cast

simplicity
• process serially
• assignment
• loop
• implicit cast

no variables
var a = 1;
var b = function() { return 1 };
a = 1
b = 1

no re-assignment
var a = 1;
var a = 2;
a = 1
a = 2
-- Multiple declarations of `Main.a'

var f = function() {
var i = 0;
return function() {
return i++;
}
};
var g = f();
g(); //=> 0
g(); //=> 1
g(); //=> 2
g(); //=> 3
g(); //=> 4

principle

write less code
• principle: as possible as you
should write less code
• development,
maintenance,
...always.

notation

aaa(bbb(\"hahaha\", 3)));
aaa (bbb \"hahaha\" 3)
aaa $ bbb \"hahaha\" 3

window.addEventListener(
\"load\",
function() { alert(\"a\") })
main = putStrLn \"a\"

var f = function(a, b) {
return a + b
};
f(8, 7) //=> 15
f a b = a + b
f 8 7 -- 15

var f = function(a) {
var g = function(b) {...};
return g(a);
};
f a = g a
where g b = ...

var fib = function(n) {
return (n == 1) ? 1 :
(n == 2) ? 1 :
fib(n-2) + fib(n-1);
};
fib 1 = 1
fib 2 = 1
fib n = fib (n-2) + fib (n-1)

(function(a) { return a + 1 })
(function(a) { return a + 1 })(3)
//=> 4
(\\a -> a + 1)
(\\a -> a + 1) 3 -- 4

a + b
(+) a b
add a b
a `add` b

List Processing
Haskell
vs
JavaScript with prototype.js

[1, 2, 3].map(function(i) {
return i + 1;
}) //=> [2, 3, 4]
map (\\i -> i + 1) [1, 2, 3]
-- [2, 3, 4]

[1, 2, 3, 4, 5].first() //=> 1
[1, 2, 3, 4, 5][3] //=> 4
head [1, 2, 3, 4, 5] -- 1
[1, 2, 3, 4, 5] !! 3 -- 4

$R(1, 10).toArray()
//=> [1, 2, ..., 10]
$R(1, Infinity).toArray()
//...
[1..10]
[1..]

head [1..] -- 1
head tail [1..] -- 2
[1..] !! 10 -- 11

curry

var f = function(a) {
return function(b) {
return function(c) {
return a + b + c }}};
f(3)(5)(7) //=> 15
f a b c = a + b + c
f a b = (\\c -> a + b + c)
f a = (\\b -> (\\c -> a + b + c))
f = (\\a -> (\\b -> (\\c -> a + b + c)))
f 3 5 7 -- 15

f a b = a + b
f a b = (+) a b
f = (+)
addOne a = 1 + a
addOne a = (+) 1 a
addOne = (+) 1
addOne = (1 +)
map (1 +) [1, 2, 3]

list comprehension

tmp = [];
[1, 2].each(function(x) {
[10, 20].each(function(y) {
tmp.push(x + y)
})
});
[ x + y | x <- [1, 2], y <- [10, 20]]
{x + y|x ∈ X, y ∈ Y }

tmp = [];
$R(1, Infinity).each(function(x) {
if (x % 2 == 0 && x < 10) {
tmp.push(x)
}
});
[ x | x <- [1..], x `mod` 2 == 0, x < 10]
{x|x ∈ N, x ≡ 0 mod 2, x < 10}

fib again
h (+) fib (tail fib)
fib = 1 : 1 : zipWit

how to use
• sudo port install ghc
• HotMac :-)
• runghc a.hs
• ghc a.hs && ./a.out
• ghci

for what?
• draft
• step up
• production

Monadius

HSP

Haskell
Scheme
Prolog

• lazy evaluation
• monad
• type inference

thank you!