test.hs

greet :: String -> String
greet name
  | name == "Juan" = niceGreeting ++ " " ++ name
  | otherwise = badGreeting ++ " " ++ name
  where niceGreeting = "Hello! So very nice to see you,"
        badGreeting  = "Oh! Pfft. It's you."

greet' :: String -> String
greet' "Juan" = niceGreeting ++ " " ++ "Juan"
  where niceGreeting = "Hello! So very nice to see you,"
greet' name   = badGreeting  ++ " " ++ name
  where badGreeting  = "Oh! Pfft. It's you."