George, Thanks for the response. If i take out the AllowUndecidableInstances i get no complaints and the compiler hangs. See thishttp://paste.pocoo.org/show/95523/. Thus, i can find no observable difference for this flag in this particular code sample. Best wishes, --greg On Mon, Dec 15, 2008 at 2:34 PM, George Pollard wrote:

This is precisely what AllowUndecidableInstances allows; the type checking becomes possibly non-terminating. It should *eventually* terminate because the stack depth is restricted.

- George

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