Hello! I could now find the place, where an error occurs. In my program, I have following statement: do ... classifiedImagesWithData <- (readClassifiedImages trainingSet) readClassifiedImages is defined as follows: readClassifiedImages :: [ClassifiedImage] -> [IO (ClassifiedImage, Image)] readClassifiedImages classifiedImages = (map readClassifiedImagesSelector classifiedImages) When I load the file with the definition of this function into GHCi and then type in ":t readClassifiedImages", I get the output readClassifiedImages :: [ClassifiedImage] -> [IO (ClassifiedImage, Image)] which is what I want. However, when in the program I insert the statement classifiedImagesWithData :: [IO (ClassifiedImage, Image)] so that it becomes do ... classifiedImagesWithData <- (readClassifiedImages trainingSet) classifiedImagesWithData :: [IO (ClassifiedImage, Image)] -- error line I get the error <error> ExperimentalYaleFaceDb.hs:28: Couldn't match `[IO (ClassifiedImage, Image)]' against `IO (ClassifiedImage, Image)' Expected type: [IO (ClassifiedImage, Image)] Inferred type: IO (ClassifiedImage, Image) When checking the type signature of the expression: classifiedImagesWithData :: [IO (ClassifiedImage, Image)] In a 'do' expression: classifiedImagesWithData :: [IO (ClassifiedImage, Image)] </error> Line 28 is the line marked with "error line" in the code snippet above. I don't understand why this typing error occurs even though the readClassifiedImages definition seems to be correct (at least, GHCi loads the file, where it is located without complaints). Any hint is highly appreciated. Best regards Dmitri Pissarenko -- Dmitri Pissarenko Software Engineer http://dapissarenko.com