There are a few things wrong with this...
> uni :: IO () -> Float
> uni = do
> xs <- newStdGen
> let
> m = (head (randoms xs) :: Float )
presumably, you want 'uni' to produce a random float. in this case, it
has the wrong type; it is actually an IO action that returns a Float,
hence it's type should be:
uni :: IO Float
furthermore, IO actions (and functions in general) need to return
something; since you're using 'do' notation, you need to have a call to
return, something like:
uni = do xs <- newStdGen
let m = (head (randoms xs) :: Float)
return m -- return the head
or more simply
uni = do xs <- newStdGen
return (head (randoms xs))
then, since do { x <- f ; y x } really means "f >>= \x -> y x" which is
"f >>= y", you could write this as
uni = newStdGen >>= return . head . randoms
(if that doesn't make sense, don't worry)
> doubleit :: Float -> Float
> doubleit n = 2.0*n
this is fine
> main = print (doubleit uni)
here's another problem. the type of uni is IO Float. the type of
doubleit is Float -> Float. You can't pass an IO Float as a parameter
instead of a float. what you need to do is perform the action uni, get
the result, pass it to doubleit and then print that, something like:
main = do v <- uni
print (doubleit v)
again, you can rewrite this:
main = uni >> print . doubleit
hope that made some sense, i gotta run
- hal
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