[Haskell-cafe] Non-deterministic behaviour of aeson's parser

I am observing a non-deterministic behaviour of aeson's parser. I'm writing here in addition to filing a bug report [1] to draw attention to this (pretty scary) problem. To try to reproduce this problem, do this: git clone https://gist.github.com/5604887.git aeson cd aeson ghc aeson.hs ./aeson | sort | uniq -c This is my result: 32 Left "key \"module\" not present" 55 Left "When parsing the record SymValue of type Main.SymValueInfo the key fixity was not present." 1913 Right () Can others reproduce this in their environments? Does anyone have ideas about where the bug may lie? Many aeson's dependencies do unsafe IO stuff that could lead to such consequences. Roman [1]: https://github.com/bos/aeson/issues/125