Yes, largely the choice to define foreach was made to try and make it look more imperative, I showed it to an imperative programmer to try and convince him that you could program in an imperative way in Haskell if you really wanted to, that and I thought it'd an imperative style would make an interesting addition to the evolution of a Haskell programmer. Bulat Ziganshin wrote:
Hello Bryan,
Saturday, July 22, 2006, 4:40:58 AM, you wrote:
Forgive me for not understanding, but I was hoping you would explain a choice you made in your code. Why did you define foreach and then use
foreach [1..n] (\x -> modifySTRef r (*x))
Instead of simply using
mapM_ (\x -> modifySTRef r (*x)) [1..n]
because it looks just like for/foreach loops in imperative languages. look at this:
import Control.Monad import Data.IORef
infixl 0 =:, +=, -=, .=, <<= ref = newIORef val = readIORef a=:b = writeIORef a b a+=b = modifyIORef a (\a-> a+b) a-=b = modifyIORef a (\a-> a-b) a.=b = ((a=:).b) =<< val a for :: [a] -> (a -> IO b) -> IO () for = flip mapM_
newList = ref [] list <<= x = list =:: (++[x]) push list x = list =:: (x:) pop list = do x:xs<-val list; list=:xs; return x
main = do sum <- ref 0 lasti <- ref undefined for [1..5] $ \i -> do sum += i lasti =: i sum .= (\sum-> 2*sum+1) print =<< val sum print =<< val lasti
xs <- newList for [1..3] (push xs) xs <<= 10 xs <<= 20 print =<< val xs