Can I get the internal name of a package at runtime?

Edward Z. Yang ezyang at
Sat Oct 14 16:01:42 UTC 2017

Hi MarLinn,

The mangling name is "z-encoded".  It is documented here:


Excerpts from MarLinn's message of 2017-10-14 17:35:28 +0200:
> Hi.
> I'm experimenting with plug-ins right now. I did manage to dynamically 
> load functions at runtime. The caveat: Something (cabal? ghc?) mangles 
> the package names. For example, to load a function called "theFunction" 
> from a module called "Callee" in a package "Plugin", I had to address it 
> via the name 
> "Pluginzm0zi0zi0zi0zm2QaFQQzzYhnKJSPRXA7VtPe_Callee_theFunction_closure". 
> O…K. Most parts of that are clear, and thanks for making my package 
> cooler by appending a "z", but who is this Ozi guy and why is he rapping 
> about modems? Without knowing Ozi, the only way I found to get at this 
> magic string is to manually look at the actual ELF-header of the 
> compiled module. While that might be a robust way, it seems neither 
> portable nor elegant.
> The "plugins" library failed too, probably for the same reason. (Or it's 
> under-documented. Probably both.) The "dynamic-loader" library does 
> something via c, therefore no.
> Which brings me to the question: Is there any way for a module to get at 
> its own internal package name? Or even at the internal name of an 
> external package? If not, can I somehow recreate the magic mangling at 
> runtime? At first I thought the functions in the "Module", "Name" etc 
> modules of GHC might help – but it seems I either need an existing Name 
> (that I have no idea how to get) or I have to create one (with no idea 
> what magic mangler to call).
> I'm asking this question here rather than on café as I feel that if 
> there is a solution, it's probably buried in the details of GHC.
> Thanks for any suggestions,
> MarLinn

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