The programming language users might want to apply transformations to source code written in the language -- which now means they need to write brand new pa

The programming language users might want to apply transformations to source code written in the language -- which now means they need to write brand new parsers from scratch to do these transformations. That would be Doing It Wrong. Tools like clang-format (source formatting) and clang-modernize (source transformation to use new language features) use exactly the same parser library — among other things — as the compiler proper.