Hello! I have now another problem. I have a function readClassifiedImages :: [ClassifiedImage] -> [IO (ClassifiedImage, Image)] readClassifiedImages classifiedImages = map readClassifiedImagesSelector classifiedImages data ClassifiedImage = ClassifiedImage {imageFileName :: String, subjectID :: String} deriving Show I have another function, which should transform [IO (ClassifiedImage, Image)] to [IO Image]. For a certain operation, I need just the images without the information contained in the data type ClassifiedImage. So I defined following function: getImages :: [IO (ClassifiedImage, Image)] -> [IO Image] getImages classifiedImages = map snd classifiedImages First argument of it has the same type as the "return value" of function readClassifiedImages. Then I created following program. <program> module ExperimentalYaleDb where import Lik main = do let trainingSet = [(ClassifiedImage "../data-test/yalefaces- pgm/subject01.centerlight.pgm" "subject01"), (ClassifiedImage "../data-test/yalefaces- pgm/subject02.centerlight.pgm" "subject02"), (ClassifiedImage "../data-test/yalefaces- pgm/subject03.centerlight.pgm" "subject03"), (ClassifiedImage "../data-test/yalefaces- pgm/subject04.centerlight.pgm" "subject04"), (ClassifiedImage "../data-test/yalefaces- pgm/subject05.centerlight.pgm" "subject05"), (ClassifiedImage "../data-test/yalefaces- pgm/subject06.centerlight.pgm" "subject06"), (ClassifiedImage "../data-test/yalefaces- pgm/subject07.centerlight.pgm" "subject07"), (ClassifiedImage "../data-test/yalefaces- pgm/subject08.centerlight.pgm" "subject08"), (ClassifiedImage "../data-test/yalefaces- pgm/subject09.centerlight.pgm" "subject09"), (ClassifiedImage "../data-test/yalefaces- pgm/subject10.centerlight.pgm" "subject10")] -- read images from files classifiedImagesWithData <- (readClassifiedImages trainingSet) -- fetch images only from classifiedImagesWithData allImages <- (getImages classifiedImagesWithData) return 0 </program> When I try to run this program in GHCi, I'm getting this error message <error> C:\dapWork\lik\sw\src>startghci Lik.hs:14: Couldn't match `(a, IO Image)' against `IO (ClassifiedImage, Image)' Expected type: [(a, IO Image)] Inferred type: [IO (ClassifiedImage, Image)] In the second argument of `map', namely `classifiedImages' In the definition of `getImages': getImages classifiedImages = map snd classifiedImages Failed, modules loaded: HUnit, HUnitText, HUnitBase, HUnitLang. *HUnit> </error> where "Lik.hs:14" denotes the line getImages classifiedImages = map snd classifiedImages How can I solve this problem? TIA Dmitri Pissarenko -- Dmitri Pissarenko Software Engineer http://dapissarenko.com