Re: [Haskell-cafe] What is this function? (RESOLVED)

Hi Luke, Thankyou so much. I need the sequence function. What I was after was this: class Scramblable a where scramble :: a -> [a] instance Scramblable [MyType] where scramble values = sequence (map scramble values) instance Scramblable MyType where scramble myType = {- blah blah -} I was basically after exhaustively generating lots ASTs given a template AST with lots of leaf values changed. Thanks, -John On Thu, Oct 16, 2008 at 8:39 PM, Luke Palmer wrote:

2008/10/16 John Ky :

...

Hi,

I've written this function here:

scramble [] = [] scramble [x] = [[z] | z <- scramble x] scramble (x:xs) = [(y:z)|y <- scramble x, z <- scramble xs]

and (I think) it roughly does what I want it to:

*Main> scramble ([]::[Int]) [] *Main> scramble ([1]::[Int]) [[1],[2]]

So, um, this is nonsense. You've given it only 1, and yet it outputs a 2, yet there is no mention of addition or the literal 2 anywhere in your function.

This function looks a lot like the more sensible:

scramble' n xs = sequence (replicate n xs)

...

...

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scramble' 0 [1,2,3] [[]] scramble' 1 [1,2,3] [[1],[2],[3]] scramble' 2 [1,2,3] [[1,1],[1,2],[1,3],[2,1],[2,2],[2,3],[3,1],[3,2],[3,3]]

Where your examples all had [1,2] as the argument.

Luke