runEditor: if 'lastEdit' is empty, edit lastModule().
runEditor: if 'lastEdit' is empty, edit lastModule().

=> for an interpreter session with only the Prelude loaded,
   interpret ":edit" as wanting to edit Prelude.hs

FranklinChen/Hugs,FranklinChen/Hugs,FranklinChen/Hugs,FranklinChen/Hugs,FranklinChen/Hugs,FranklinChen/Hugs,FranklinChen/Hugs