Re: [Haskell-cafe] Getting an attribute of an object

13 Feb 2005

      Hello!

Thanks for your answer!
...
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.
I've tried that and wrote

<code-snippet>
do...
let classifiedImagesWithData = ((return trainingSet) >>= readClassifiedImages)
ciwd <- (sequence classifiedImagesWithData)
let allImages = (getImages ciwd)
</code-snippet>

Now, I get the error

<error>
Compiling ExperimentalYaleDb ( ExperimentalYaleFaceDb.hs, interpreted )

ExperimentalYaleFaceDb.hs:41:
     Couldn't match `[]' against `IO'
         Expected type: [[a]]
         Inferred type: [IO (ClassifiedImage, Image)]
     In the first argument of `sequence', namely
         `classifiedImagesWithData'
     In a 'do' expression: ciwd <- (sequence classifiedImagesWithData)
Failed, modules loaded: TestLik, Lik, HUnit, HUnitText, HUnitBase, HUnitLang.
</error>

at line

ciwd <- (sequence classifiedImagesWithData)

Are there any other options?

Thanks in advance

Dmitri Pissarenko

PS: Maybe the error is rooted in code parts other than those given here. In
the attachment there is the code of the main program
(ExperimentalYaleFaceDb.hs) and the function definitions (Lik.hs).
--
Dmitri Pissarenko
Software Engineer
http://dapissarenko.com