Most popular languages don't let you define custom syntactic forms. C and C++ have a preprocessor, Scala has macros and you can squint and pretend that passing

Most popular languages don't let you define custom syntactic forms. C and C++ have a preprocessor, Scala has macros and you can squint and pretend that passing blocks in Ruby counts, but that's it. It's not a killer feature for the vast majority of programs, Go's boneheaded straightforwardness is a good counterexample.