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What seems to be happening is that the Arrow module in gtk2hs is clashing with the Arrow module in the lang package. As far as I can tell this all looks perfectly normal, so why don't we this kind of problem all the time? What's special about Arrow?

How does it get resolved in the libHS*.a case? How does the system linker resolve the ambiguity when ghci's linker cannot?

The static linker will simply pick the first __stginit_Arrow it finds when searching libraries. In actual fact, you're better off with the linking error, because the static linking behaviour is

2003年06月17日(火)の20時15分に Simon Marlow 曰く: likely to result

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in crashes at runtime.

I see, interesting.

In this case gtk2hs.o was generated by ghc-pkg, but naively, can I ask, is it not possible to detect this claiming of module names at buildtime?

Yes, in theory, but it would mean searching the entire search path to find all the .hi files for a module, rather than stopping as soon as you've found one. Cheers, Simon