Am Mittwoch 10 Februar 2010 05:49:46 schrieb edgar klerks:

Hello all,

I have a very interesting alternative solution of the problem. First I generate a tree with all the permutations:

eg if I want to find al permutations of ao, I get the following tree

[a @]

[o 0] [o 0]

Then I walk trough the tree so I can print it. There is only one ugly thing. Showtree' returns a string (in our example aoa0@o@0). To make it a list i put a \n between a left and right node and then use lines to make it a list of strings. Can someone point me in the right direction how to beautify it a bit?

I also have an annoying problem with gmail and firefox. It seems it doesn add my posts to the current thread, but starts a new one. Oh well think I switch to evolution.

I will review all yours solutions tomorrow. I saw some very beautifull

Apparently, it doesn't set the in-reply-to field. That should be configurable. things.

With kind regards,

Edgar Klerks

module Main where import Data.Char

data WordTree = Chain (Char,WordTree)

Why add the extra tuple? Better: Chain Char WordTree

| Choice (Char, WordTree) (Char, WordTree)

Again, the tuples aren't necessary.

| Stop

instance Show WordTree where show = unlines.showTree

type Rule = (Char, Char)

I think it would be better to have type Rule = (Char,[Char]) or even data Rule a = Sub a [a] or use a Map a [a]. You gain more flexibility that way and can use the same code if you can replace a Char (or whatever) with one of any number of possibilities. The WordTree type would then become data WordTree = Branch [(Char, WordTree)] | Tip type Rules = Map Char [Char] rules :: Rules rules = fromList [('a',['a','@']),('l',['l','|'])] subs :: Char -> Rules -> [Char] subs c rs = findWithDefault [c] c rs buildTree :: String -> Rules -> WordTree buildTree (c:cs) rs = let st = buildTree cs rs in Branch [(s,st) | s <- subs c rs] buildTree "" _ = Tip showTree (Branch ts) = [c:xs | (c,st) <- ts, xs <- showTree st] showTree Tip = [""]

type Rules = [Rule]

infixl 4 ==>

a ==> b = (a,b)

rules :: Rules rules = [ 'a' ==> '@', 'l' ==> '|']

buildTree :: String -> Rules -> WordTree buildTree [] r = Stop buildTree (c:cs) r = case lookup c r of Just a -> Choice (a, buildTree cs r) (c, buildTree cs r)

Share the subtree, Just a -> let st = buildTree cs r in Choice (a,st) (c,st)

Nothing -> Chain (c, buildTree cs r)

showTree a = lines $ showTree' a []

showTree' (Chain (a,b)) p = a : showTree' b p showTree' (Choice (a,b) (c,d)) p = c : showTree' d p ++ "\n" ++ (a : showTree' b p) showTree' (Stop) p = p

showTree :: WordTree -> [String] showTree (Chain (a,b)) = [a:xs | xs <- showTree b] showTree (Choice (a,b) (c,d)) = [a:xs | xs <- showTree b] ++ [c:ys | ys <- showTree d] showTree Stop = [""]