Max Vasin wrote:
Bryn Keller <[EMAIL PROTECTED]> writes:
Hi Max,
Hello Bryn,
Thanks for pointing this out. It's odd that I don't see that anywhere
in the docs at the HToolkit site:
http://htoolkit.sourceforge.net/doc/hsql/Database.HSQL.html but GHC
certainly believes it exists. However, this doesn't actually solve the
problem. Substituting toSqlValue for show in printRow' gives the same
compile error:
Main.hs:22:18:
Ambiguous type variable `a' in the constraint:
`SqlBind a' arising from use of `getFieldValue' at Main.hs:22:18-30
Probable fix: add a type signature that fixes these type variable(s)
So, like with (show (read s)), we still can't use the function until
we've established a definite type for the value, not just a type
class.
Yeah...
Some more RTFSing shows that we have the
getFieldValueType :: Statement -> String -> (SqlType, Bool)
which allows us to write
printRow stmt = do (id :: Int) <- getFieldValue stmt "ID"
let (codeType, _) = getFieldValueType stmt "Code"
codestr <- case codeType of
SqlChar _ -> do (c :: String) <- getFieldValue stmt
"Code"
return (toSqlValue c)
SqlInteger -> do (i :: Int) <- getFieldValue stmt
"Code"
return (toSqlValue i)
-- etc for all SqlType data constructors
putStrLn (unwords [show id, codestr])
At least it compiles. But it's ugly :-(
Ah, good point! Ugly it may be, but at least it works. Thanks for the idea!
Bryn
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