I have this little demo which I use for sixth formers which includes calculating in fairly rapid order the sum of the digits of the 10^9th Fibonacci number. (I haven't got enough physical memory to do the same for the 10^10th number without thrashing...) It fell over on a flashy new macbook I was going to use for the presentation the other day; indeed I found I couldn't even calculate the sum of the digits of the 10^6th number. I've reduced the problem to calculating numbers as large as 2^10000000 (as an Integer, of course), which works on all the ghci 7.8.4 implementations I can find on various machines around the department, but which falls over on the 8.0.1 implementation on my macbook. 2^1000000 is fine, but 2^10000000 causes a bus error which may well be a stack overflow in libHSinteger-gmp-1.0.0.1-ghc8.0.1.dylib I don't seem to have easy access to 8.0.1 elsewhere or other implementations on a mac. Does anyone have a handle on whether this is a problem with the sizing of the mac implementation or whether it is a pervasive 8.0.1 problem? Either way, it doesn't seem friendly that it manifests as an uncaught bus error.