module Chap3 where {
fact :: Integer -> Integer;
fact n = if n==0 then 1 else n*fact(n-1);

{- Preludeに定義済み
length :: [a] -> Integer;
length []     = 0;
length (x:xs) = 1 + length xs;
 -}

append           :: [a] -> [a] -> [a];
append [] ys      = ys;
append (x:xs) ys  = x : (append xs ys);

{- Preludeに定義済み
reverse   :: [a] -> [a];
reverse [] = [];
reverse (x:xs) = append (reverse xs) [x];
 -}

-- shunt は revの補助関数
shunt          :: [a] -> [a] -> [a];
shunt ys []     = ys;
shunt ys (x:xs) = shunt (x:ys) xs;

rev   :: [a] -> [a];
rev xs = shunt [] xs;

{- Preludeに定義済み
zip :: [a] -> [b] -> [(a,b)];
zip (a:as) (b:bs) = (a,b) : zip as bs;
zip _       _     = [];
 -}

pow4 x = let { y = x*x } in y*y;
head ys = let { (x:xs) = ys } in x;

repeat  :: a -> [a];
repeat x = let { xs = x:xs } in xs;

data Direction = Up | Down | Left | Right;

data Tree a = Branch (Tree a) a (Tree a) | Empty;

from :: Integer -> [Integer];
from n = n : from (n+1);

{- Preludeに定義済み
take :: Integer -> [a] -> [a];
take 0 _      = [];
take _ []     = [] ;
take n (x:xs) = x : take (n-1) xs;
 -}

unit :: a -> [a];
unit a = [a];

bind :: [a] -> (a -> [b]) -> [b];
bind []     _ = [];
bind (x:xs) f = append (f x) (bind xs f)
}