if you point to a package source code located on the hard drive and that package has c source files, it will give runtime errors in stack ghci.

For example hdbc-odbc errors out in stack ghci when trying to connect to db. It gives following error:

/usr/local/lib/ghc-7.10.2/bin/ghc: symbol lookup error: /tmp/ghc25980_0/libghc_1.so: undefined symbol: SQLSetConnectAttr

The function SQLSetConnectAttr is calling a c module hdbc-odbc-helper.c that is bundled with hdbc-odbc package.

Loading hdbc-odbc from hackage works fine in stack ghci.

Stack build also works fine.