This has something of the Smalltalk image-based approach (and the author might enjoy using a Smalltalk development environment). IMO the costs outweigh the gains - it's worth decoupling programming a computer from using it. When source code is just text files, you can manipulate it with lots of powerful tools; even better, you can use tools from different languages whose authors never talked to each other. When the shell and the compiler are just user-mode programs, they can iterate much faster, and you can choose one that suits your style. You can use the same program for both, if you really want to - for a few weeks I used tclsh as my login shell - but it turns out the tools you need for programming are quite different from those for general computer use. Division of labour is ultimately a good thing, even if it means less of the population has any specific skillset.