| > > Since the Report states that the derived Show instances only insert | > > parentheses where needed and that the derived Read instances can | > > read the output produced by show, I would suggest to change all | > > occurences of {showsPrec 10,readsPrec 10} to {showsPrec 0,readsPrec 0} | > > in the above code. | > | > That seems like a reasonable suggestion, but it doesn't fix the bug. | | Could you please explain why not? It seems to work fine in my tests here, | at least with the given example. Apologies. For some reason, maybe a file version mismatch, the example continued to fail when I first tried your solution. That puzzled me, because indeed your solution is correct, and the example does now work when I run it again. Regards, Malcolm