[Haskell-cafe] How efficient is read?

[Tom Hawkins]

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