From: Kristof Bastiaensen <kristof@...>
Date: 2006-07-28T22:05:10+09:00
Subject: Re: For performance, write it in C

On Fri, 28 Jul 2006 03:39:09 -0700, William James wrote:

> 
> Kristof Bastiaensen wrote:
> 
>> -------------------- start of latin.curry ----------------------------
>> -- upto is a nondeterministic function that evaluates to
>> -- a number from 1 upto n
>> upto 1 = 1
>> upto n | n > 1 = n ? upto (n-1)
>>
>> -- check if the lists r s have no element with the same value at the
>> -- same position
>> elems_diff r s = and $ zipWith (/=) r s
>>
>> -- extend takes a list of columns, and extends each column with a
>> -- number for the next row.  It checks the number agains the column and
>> -- against the previous numbers in the row.
>>
>> extend :: [[Int]] -> Int -> [[Int]]
>> extend cols n = addnum cols [] where
>>     addnum [] _ = []
>>     addnum (col:cs) prev
>>         | x =:= upto n &
>>           (x `elem` prev) =:= False &
>>           (x `elem` col) =:= False = (x:col) : addnum cs (x:prev)
>>         where x free
>>
>> latin_square n = latin_square_ n
>>     where latin_square_ 0 = replicate n []  -- initalize columns to nil
>>           latin_square_ m | m > 0 = extend (latin_square_ (m-1)) n
>>
>> square2str s = unlines $ map format_col s
>>     where format_col col = unwords $ map show col
>>
>> main = mapIO_ (putStrLn . square2str) (findall (\s -> s =:= latin_square 5))
>> ------------------------- end latin.curry -----------------------------
> 
> I don't see where elems_diff is used after it is defined.

Heh, you are right!  I defined it, and then when I didn't need it I forgot
to remove it.

Thanks for noting,
Kristof