From: hipster <hipster@...4all.nl>
Date: 2000-11-14T20:28:40+09:00
Subject: [ruby-talk:6357] Re: Another Smalltalk control structure idea

On Tue, 14 Nov 2000  19:36:21 +0900, Hugh Sasse Staff Elec Eng wrote:
> > > Hmm. What's this here? Your might want to consider "reduce: a
> > > generalized inject function"
> > > (http://www.xs4all.nl/~hipster/lib/ruby/reduce) as a starting
> > > point. It's already written in Ruby. (What a coincidence! :-)
> > > And it happens to have the name I prefer.
> > 
> > Credits go to Dave Thomas, see [ruby-talk:03178]. I merely archived
> > it for posterity.
> 
> Is it any help to remind people that Python has
>     map
>     filter
>     reduce
> which operate on lists?  See:
> http://www.python.org/doc/current/lib/built-in-funcs.html
> for what they do.

The following list contains all standard list operations as defined in
the Haskell prelude (i.e. std. library), including examples. It would
be nice to have some of them in a std. Ruby lib, like take, drop,
takeWhile, zip etc.

Talking about Haskell: infinite lists and lazy evaluation, maybe an
idea for Ruby 1.8?   <now _that_ would be cool>   8)

	Michel


-- prelude list functions
list = [1..10]

e1 = head list			--> 1
e2 = last list			--> 10
e3 = tail list			--> [2..10]
e4 = init list			--> [1..9]
e5 = null []			--> True
e6 = null list			--> False
e7 = list ++ list		--> [1..10,1..10]
e8 = map (*2) list		--> [2,4..20]
e9 = filter (>7) list		--> [8,9,10]
e10 = concat [list,list]	--> [1..10,1..10]
e11 = length list		--> 10
e12 = list!!0			--> 1
e13 = list!!3			--> 4
e14 = list!!(length list - 1)	--> 10
-- (fold-left  f x0 '(x1 x2 x3)) = (f (f (f x0 x1) x2) x3)
e15 = foldl (+) 0 list		--> 55 (0+(1+(2+..(10))))
e16 = foldl (*) 1 list		--> 3628800 (1*1*2*..*10 = 10!)
e17 = foldl1 (+) list		--> 55 (1+(2+(3+..(10))))
e18 = scanl (+) 0 list		--> [0,1,3,6,10,15,21,28,36,45,55]
e19 = scanl1 (+) list		--> [1,3,6,10,15,21,28,36,45,55]
-- (fold-right f x0 '(x1 x2 x3)) = (f x1 (f x2 (f x3 x0)))
e20 = foldr (+) 0 list		--> 55 (1+(2+(3+..(10+0))))
e21 = foldr1 (+) list		--> 55 (1+(2+(3+..(10))))
e22 = scanr (+) 0 list		--> [55,54,52,49,45,40,34,27,19,10,0]
e23 = scanr1 (+) list		--> [55,54,52,49,45,40,34,27,19,10]
e24 = iterate (cos) 4		--> [4,cos(4),cos(cos(4)),..]
e25 = repeat 1			--> [1,1,1,..]
e26 = replicate 4 'a'		--> "aaaa"
e27 = cycle [1,2,3]		--> [1,2,3,1,2,3,..]
e28 = take 4 list		--> [1,2,3,4]
e29 = drop 4 list		--> [5,6,7,8,9,10]
e30 = splitAt 4 list		--> ([1,2,3,4],[5,6,7,8,9,10])
e31 = takeWhile (<4) list	--> [1,2,3]
e32 = dropWhile (<4) list	--> [4,5,6,7,8,9,10]
e33 = span (<4) list		--> ([1,2,3],[4,5,6,7,8,9,10])
e34 = break (==7) list		--> ([1,2,3,4,5,6],[7,8,9,10])
e35 = lines "A\nB\nC"		--> ["A","B","C"]
e36 = words "ab cd ef"		--> ["ab","cd","ef"]
e37 = unlines ["A","B","C"]	--> "A\nB\nC"
e38 = unwords ["ab","cd","ef"]	--> "ab cd ef"
e39 = reverse list		--> [10,9..1]
e40 = and [True,False]		--> False
e41 = or [True,False]		--> True
e42 = any (even) list		--> True
e43 = all (even) list		--> False
e44 = elem 4 list		--> True
e45 = notElem 11 list		--> True
e46 = lookup 2 [(1,2),(2,4)]	--> Just 4
e47 = sum list			--> 55
e48 = product list		--> 3628800
e49 = maximum list		--> 10
e50 = minimum list		--> 1
--e51 = concatMap
e52 = zip [1,2] [3,4]		--> [(1,3),(2,4)]
e53 = zip3 [1,2] [3,4] [5,6]	--> [(1,3,5),(2,4,6)]
e54 = unzip [(1,3),(2,4)]	--> ([1,2],[3,4])
e55 = unzip3 [(1,3,5),(2,4,6)]	--> ([1,2],[3,4],[5,6])