Sorry, I was actually trying to use this as an example for something more complicated I am trying to do. In this example, why would the inferred type be "IO ()"
aa :: String -> String
aa instr = do
putStrLn "abc"
putStrLn "abc"
return "Az"
Couldn't match expected type `[t]' against inferred type `IO ()'
In the expression: putStrLn "abc"
In a 'do' expression: putStrLn "abc"
In the expression:
do putStrLn "abc"
putStrLn "abc"
return "Az"
On 9/24/07, Sam Hughes <hughes@rpi.edu> wrote:
John Wicket wrote:
> I am still in an imperative way of thinking. In this example here; how
> would I call "putStrLn" and then set the function with a value. Eg:
>
> aa :: String -> IO ()
> aa instr = do
> putStrLn "abc"
> putStrLn "abc"
> return "123"
>
> --- The error I am getting.
>
> Couldn't match expected type `()' against inferred type `[Char]'
> In the first argument of `return', namely `"123"'
> In the expression: return "123"
> In the expression:
> do putStrLn "abc"
> putStrLn "abc"
> return "123"
Your type signature is wrong. If you want an IO action whose return
value is a String, say so:
aa :: String -> IO String