Hi all, I thought that Cont Monad is just equivalent to CPS Transformation, so if I have a monadic sum, if I run in Identity Monad, it will suck due to stackoverflow, and if I run it in Cont Monad, it will okay due to tail recursion. So I write a simple program to verify my idea. But to my surprise, the result is unreasonable due to my limited knowledge. All programs are compiled "ghc --make Test.hs -o test && ./test" Thank you in advance, the clearer the better!! (I am really confused) in the comments, suck means stackoverflow. sum0 n = if n==0 then 0 else n + sum0 (n-1) sum1 n = if n==0 then return 0 else sum1 (n-1) >>= \ v -> seq v (return (n+v)) sum2 n k = if n == 0 then k 0 else sum2 n (\v -> k (n + v)) sum3 n k = if n == 0 then k 0 else sum3 n (\ !v -> k (n + v)) sum4 n k = if n == 0 then k 0 else sum4 n (\ v -> seq v ( k (n + v))) sum5 n = if n==0 then return 0 else sum5 (n-1) >>= \ v -> (return (n+v)) -- main = print (sum0 3000000) -- suck reasonable -- main = print (flip runCont id (sum1 3000000)) -- rock 180M memory reasonable, but I am not clear why seq needed here, since its continuation is not applied until n goes to 0 -- main = print (flip runCont id (sum5 3000000)) -- suck -- why? -- main = print (flip runCont (const 0) (sum1 3000000)) -- rock 130M memory -- reasonable -- main = print (flip runCont (const 0) (sum5 3000000)) -- rock 118M memory -- reasonable -- main = print (sum2 3000000 (const 0)) -- a lot of memory (more than 1G) -- I thought sum2 is equivalent to sum5 (when sum5 is in Cont Monad), why? -- main = print (sum3 3000000 (const 0)) -- a lot of memory -- I thought sum3 is equivalent to sum1(Cont Monad), why? -- main = print (runIdentity (sum1 3000000)) -- suck -- exactly what I want -- main = print (sum3 3000000 id) -- a lot of memory -- equivalent to sum1 why? -- main = print (sum4 3000000 id) - - a lot of memory -- equivalent to sum1 why? -- main = print (sum [1 .. 3000000]) -- suck -- src sum = foldl (+) 0 -- reasonable -- main = print (foldl' (+) 0 [1 .. 3000000]) -- rock 1.5M memory -- reasonable -- Best, bob