[Haskell-beginners] stack overflow summing numbers read from a big file

When I try to run the following code on a 50M file consisting of one number per line I receive a `Stack space overflow' error and the program seems to consume a lot of memory. Why does that happen? And how can I fix the problem without increasing the Stack with -Ksize hoping that it will be big enough? Any general advice on processing big files with Haskell? -- sumFile.hs -- adapted from Real World Haskell's SumFile.hs at the beginning of -- Chapter 8 main = interact sumFile where sumFile = show . sum . map read . words ghc -o sumFile sumFile.hs ./sumFile < ./numbers