[Haskell-cafe] Re: Function to detect duplicates

[Ketil Malde]

Daniel Fischer <daniel.is.fischer at web.de> skrev:

> Am Freitag 26 Februar 2010 16:50:42 schrieb Ketil Malde:
>>> solutions = [[x1,x2,x3,x4,x5,x6,x7,x8,x9,x10]
>>>           | x1 <- [0..9]

> First digit can't be 0, so make it [1 .. 9].
> Since you use the fact that the last digit must be the 0, pull all others 
> from [1 .. 9].

Originally, I pulled from alternating odds (x1 <- [1,3..9] etc) and
evens, since this is fairly easy to deduce...  I reverted this since the
point was to use brute force.

>>> solve :: [Int] -> [[Int]]
>
> Not on a 32-bit system. Word would suffice there, but you don't know that 
> in advance, so it'd be Int64 or Integer

Hm?  The Ints are just individual digits here.

> I would make the length of the prefix a parameter of solve.

I thought about generating a list with solutions for increasing lenghts,
so that e.g. 'solve [] !! 10' would solve this particular problem.

> solve prefix =
>       case length prefix of
>         10 -> return prefix
>         l -> do
>            x <- [0 .. 9]
>             ...
>
> over the if-then-else.

Yes, much nicer.  Thanks for the feedback!

-k
-- 
If I haven't seen further, it is by standing in the footprints of giants