[Haskell-cafe] CDouble type coercion
mattcbro at earthlink.net
Sun May 14 15:00:55 EDT 2006
Thanks that helps a bit. The realToFrac type coercion works, but ultimately
that printf won't play nice. Consider this simple haskell code
-- import Data.Array.Storable
import Foreign.C.Types (CInt, CDouble )
y :: CDouble
y = 5.2
u = realToFrac(y)
test = do printf "%14.7g" u
Compiling it into GHCi I get the error,
No instance for (PrintfType (t t1))
arising from use of `printf' at test.hs:13:11-16
Probable fix: add an instance declaration for (PrintfType (t t1))
In the result of a 'do' expression: printf "%14.7g" u
In the definition of `test': test = do printf "%14.7g" u
Failed, modules loaded: none.
If I replace the printf by a standard print there is no problem. Also if I
the line with test = ... , it will load (compile) and I can then type in the
printf "%14.7g" u
and it works!
printf "%14.7g" y
fails because y is of type CDouble. At this point I think I'm giving up on
formatted printing in Haskell. It's just too persnickety.
I guess I'll just call printf via C and see what happens.
View this message in context: http://www.nabble.com/CDouble-type-coercion-t1615450.html#a4383006
Sent from the Haskell - Haskell-Cafe forum at Nabble.com.
More information about the Haskell-Cafe