IDEs like IntelliJ need to do this as they support all sorts of transformations (refactorings) while preserving the original source code as much as possible. Th

IDEs like IntelliJ need to do this as they support all sorts of transformations (refactorings) while preserving the original source code as much as possible. Their syntax trees must also handle errors, as they need to work robustly in the editor while the user is typing or otherwise has syntax errors. IntelliJ can even perform refactorings while the code has syntax or semantic errors. See this for more details: http://www.jetbrains.org/intellij/sdk/docs/basics/architectural_overview.html http://www.jetbrains.org/intellij/sdk/docs/basics/architectu...