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
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