By default, GHCi compiles Haskell source code into byte-code that is interpreted by the runtime system. GHCi can also compile Haskell code to object code: to turn on this feature, use the -fobject-code flag either on the command line or with :set (the option -fbyte-code restores byte-code compilation again). Compiling to object code takes longer, but typically the code will execute 10-20 times faster than byte-code.

Compiling to object code inside GHCi is particularly useful if you are developing a compiled application, because the :reload command typically runs much faster than restarting GHC with --make from the command-line, because all the interface files are already cached in memory.

There are disadvantages to compiling to object-code: you can't set breakpoints in object-code modules, for example. Only the exports of an object-code module will be visible in GHCi, rather than all top-level bindings as in interpreted modules.