inotify? You can get the OS to respond to filesystem events, for example, compiling as you type.
Scripting languages don't need this though.
Scripting languages don't need this though.
Did you miss the reason why we're compiling while you type? It's so that our IDE knows your codebase and can help you. It'll autosuggest things based on context rather than simply matching strings. It'll inspect your object model and stick in the right include directives for you. It'll let you rename things without having to search&replace&hope.
So yes, scripting languages do need this. At least if we're talking about things that your development environment needs to do to be considered a modern IDE.
I don't think this would be too difficult to write in vim, which has built-in auto-complete functions.