The rabbit hole goes a bit deeper I'm afraid
y :: CDouble
y = 5.2
u :: Double
u = realToFrac(y)
test = do printf "%14.7g" u
gives
Compiling Test ( test.hs, interpreted )
test.hs:14:11:
No instance for (PrintfType (t t1))
arising from use of `printf' at test.hs:14:11-16
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.
But in fact just this, gives the same error
test = do printf "%14.7g" 3.14
Now in the command line I get errors under various configurations but a few
of them
work e.g.
works
> printf "%g" u
> printf "%g" (3.14 :: Double)
do printf "%g" u
do printf "%g" (3.14 :: Double)
fails
printf "%g" y -- y is a CDouble
printf "%g" 3.14
All forms fail when compiled from a .hs file. However, this just in! I
finally got something to work,
namely this piece of code
test = do (printf "%14.7g" (u :: Double)) :: IO()
I guess the output of printf has to be disambiguated. There should probably
be a few examples of this in the library documentation. This also works, by
returning a string...
test = printf "%14.7g" (u :: Double) :: String
Thanks for the help by the way, without realtoFrac there would be no way for
me to use this at all.
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