On Sat, Jun 11, 2011 at 7:10 AM, Andrew Coppin
If you have a function that turns a parse tree back into text again, you can try verifying that a round-trip is the identity function. Except perhaps sometimes it isn't. Perhaps a given expression has more than one equivalent representation. A round-trip from string and back again is even less likely to be stable.
I find that this kind of testing works quite nicely in practice with QuickCheck, in the sense that it does a good job of finding bugs in both the unparser and the parser. It's possible, but unlikely, that you'll have a bug in the parser and a bug in the unparser that cancel one another out. Generate the ASTs; parse . unparse ought to be id, or perhaps t = t . parse . unparse for some simple transformation 't'. For example, if the parser annotates AST nodes with source positions, you may need 't' to strip them out. Kevin -- Kevin Charter kevin.charter@acm.org