GniruT questions

• Why these functions have different types in Haskell?
• How is possible to apply toUpperCase() on an empty String in Java?
• What's the complexity of this function?
• Not in scope: readMaybe, which library should I import?
• Why has "map (filter fst)" the type "[[(Bool, a)]] -> [[(Bool, a)]]"?
• Am I using randomRIO wrong?

GniruT answers