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
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