Re: [Haskell-cafe] translate imperative pseudo code into haskell

[Frerich Raabe]

On 2013-08-09 17:04, Joerg Fritsch wrote:
I would need some help to get to a reasonable function involving the
DB read, addition and multiplication.
for 0 <= i < row dimension of A

 for 0 <= j < column dimension of B

   for 0 <= k < column dimension of A = row dimension of B

     sum += (read A (i,k))* (read B(k,j))

I started like this but then somehow lost the compass:

main = do

 map my.read (map ((x,y) -> "matrixA:" ++ show row ++ ":" ++ show 
column) [ (i, j, k) | i <- [1..50], j <- [1..20], k <- [1..30] ])

You could treat lists as monads and write code which looks very much 
like your pseudo code, something like this

-- A few dummy definitions to make 'products' typecheck.
data Matrix = Matrix

rows :: Matrix -> Int
rows = undefined

columns :: Matrix -> Int
columns = undefined

readValue :: Matrix -> (Int, Int) -> Int
readValue = undefined

-- This is one way to write your pseudo code in Haskell
products :: Matrix -> Matrix -> Int
products a b = sum $ do
  i <- [1..rows a]
  j <- [1..columns b]
  k <- [1..columns a]
  return $ readValue a (i, k) * readValue b (k, j)

--
Frerich Raabe - ra...@froglogic.com
www.froglogic.com - Multi-Platform GUI Testing

_______________________________________________
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe