[Haskell-cafe] haskell platform - mac lion - installation error

Hello - I'm a new user, having some trouble installing the Haskell Platform (2011.4.0.0 64bit.pkg) on a Macbook Pro (10.7.3). I installed Xcode 4.3.1 (4E1019), then the Haskell Platform. When I double-click on the Platform package icon, I get an installation dialogue with an error message reading "Developer Tools Missing - Please install Xcode developer tools first." Are Xcode developer tools something distinct from Xcode itself? I'm mystified by this error message. Any assistance would be greatly appreciated - thank you.