JuliaLang/julia — comment on commit 3ee0fc984107d384c5416fcdaf4d947796d1f988
File:  line 0
By JeffBezanson:

Keeping the flisp parser would be like keeping around a C compiler written in assembly language. At some point, not really necessary.
You just have to be careful implementing syntax changes; you have to do a bootstrap before you can use the new syntax. And if the new syntax is not backwards-compatible, you have to first implement it, then bootstrap, then change all the files to the new syntax, then bootstrap again. If something goes wrong you get wedged and have to roll back, but that's not such a big deal.