GHC API: memory usage of loaded modules

Evan Laforge qdunkan at
Tue Nov 29 01:54:55 UTC 2016

I have a program that uses the GHC API to provide a REPL.  It winds up
taking up 200mb in RAM, as measured by GHC.Stats.currentBytesUsed, but
without the GHC API it's 5mb.  If I turn on verbose, I can see that
GHC is loading 255 modules, all loaded binary ("skipping M ( M.hs,
M.hs.o )") except the toplevel, and the memory use is zooming up as it
loads them.

I expect some memory usage from loading modules, but 195mb seems like
a lot.  If I do a 'du' on the entire obj directory (which has 401
*.hs.o files... the REPL doesn't expose everything), it's only 76mb on
disk.  How do loaded modules wind up consuming space, and is there any
way to use less space?

The thing is, all those loaded modules are part of the application
itself, so presumably they've already been linked into the binary and
loaded into memory.  The ideal would be that I could somehow reuse
that.  I imagine that I could by writing my own haskell interpreter
and making a big symbol table of all the callable functions, but I'd
rather not write my own interpreter if I can use an existing one!

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