Hi Malcolm,
This appears to be a cpphs bug. For the following code
#define x (1 == 1)
#if x
YES
#else
NO
#endif
cpphs 1.18.1 prints NO, while the expected output (and the output GNU
cpp produces) is YES. If parentheses around 1 == 1 are removed, or if x
is inlined manually, then cpphs correctly prints YES.
This affects GHC 7.8 users in a serious way: GHC 7.8 uses cpphs, and the
above code is a simplified version of macros generated by cabal.
For this reason, for instance, type-eq 0.4.1 cannot be build by GHC 7.8
RC1, despite the proper CPP guards.
Roman
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