[Haskell-cafe] How efficient is read?

I have a lot of structured data in a program written in a different language, which I would like to read in and analyze with Haskell. And I'm free to format this data in any shape or form from the other language. Could I define a Haskell type for this data that derives the default Read, then simply print out Haskell code from the program and 'read' it in? Would this be horribly inefficient? It would save me some time of writing a parser. -Tom