Hello Neil, It looks like my second message got eaten. Let's try again.
1) Is there any way to do the two compilations sharing some cached state, e.g. loaded packages/.hi files, so each compilation goes faster.
You can, using withTempSession in the GhcMonad. The external package state will be preserved across calls here, but things put in the HPT will get thrown out.
2) Is there any way to do the link alone through the GHC API.
I am confused by your code. There are two ways you can do linking: 1. Explicitly specify all of the objects to link together. This works even if the source files aren't available. 2. Run ghc --make. This does dependency analysis to figure out what objects to link together, but since everything is already compiled, it just links. Your code seems to be trying to do (1) and (2) simultaneously (you set the mode to OneShot, but then you call load which calls into GhcMake). If you want to use (1), stop calling load and call 'oneShot' instead. If you want to use (2), just reuse your working --make code. (BTW, how did I figure this all out? By looking at ghc/Main.hs). Cheers, Edward