Perhaps try:
do ...
ciwd <- sequence classifiedImagesWithData
let allImages = (getImages ciwd)
...
as it seems like you're trying to gave getImages act on a value of
type [IO (ClassifiedImage, Image)]. Applying sequence to
classifiedImagesWithData will turn it into an IO [(ClassifiedImage,
Image)] by doing the natural thing, from which you can pull out the
list to apply getImages to.
- Cale
On Sat, 12 Feb 2005 21:10:31 +0100, Dmitri Pissarenko
Hello!
Sorry that I bother you again with my problem.
It may be you'd profit from reading some of the Monad tutorials out there.
I followed your advice and read the "All about monads" tutorial. After I've done that I could fix one problem.
But now there is another one.
In the main program, there is following piece of code
<code-snippet> let classifiedImagesWithData = ((return trainingSet) >>= readClassifiedImages)
let allImages = (getImages classifiedImagesWithData) </code-snippet>
Signatures of readClassifiedImages and getImages are
readClassifiedImages :: [ClassifiedImage] -> [IO (ClassifiedImage, Image)] getImages :: [(ClassifiedImage, Image)] -> [Image]
readClassifiedImages does some file I/O, so it is OK when its result is in the IO monad.
getImages does not do any IO related stuff, so I declared it without the IO monad.
The line
let allImages = (getImages classifiedImagesWithData)
of the above code snippet leads to following error:
<error> ExperimentalYaleFaceDb.hs:43: Couldn't match `(ClassifiedImage, Image)' against `IO (ClassifiedImage, Image)' Expected type: [(ClassifiedImage, Image)] Inferred type: [IO (ClassifiedImage, Image)] In the first argument of `getImages', namely `classifiedImagesWithData' In the definition of `allImages': allImages = (getImages classifiedImagesWithData) Failed, modules loaded: TestLik, Lik, HUnit, HUnitText, HUnitBase, HUnitLang. </error>
Is there a way to fix this problem apart from changing signature of getImage?
Thanks in advance
Dmitri Pissarenko -- Dmitri Pissarenko Software Engineer http://dapissarenko.com
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