-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 I have got a little further by defining the following functions and I now have a better defined question. - --Takes a list and converts it to a n-ary tuple - --i.e. Generates functions like [String] -> (a,a,a) listToTuple i = lam [Pvar "xs"] (tup ([ infixE (Just $ var "xs") (var "!!") (Just $ lit (Integer n)) | n <- [0..(i-1)] ])) - --Casts an n-ary tuple of type (String,String,..) - --i.e. Generates functions like (a,a,a) -> (Int,Bool,Int) cast i = lam [Ptup pats] (tup [ app (var "read") v | v <- vars]) where pats = [ Pvar $ show n | n <- [1..i] ] vars = [ var $ show n | n <- [1..i] ] So, I can now define a function f, f :: [String] -> (Int, Bool) f = $(cast 2) . $(listToTuple 2) but I can still see no way to infer the size of the tuple purely from the declared type signature. Tom On Wed, 2 Jul 2003 11:56 am, Thomas L. Bevan wrote:
Hi,
I'm struggling to write the following function in Template Haskell.
I have a phantom type,
data HTMLPage a = HTMLPage FilePath
This type points to an HTML file, where 'a' refers to the return type of the posted form. So, mostly, I would expect types like HTMLPage (String, String, Date, Int)
Where this represented a form the returned someone's first name, last name, dob and age.
So, I want a function that will take the returned name/value pairs and cast them into the matching type.
eg.
readForm :: Read a => [(String,String)] -> HTMLPage a -> a
Can anyone give me any pointers or am I better off just abandoning this approach?
Tom
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