Using curly braces for blocking is a non-starter because they're used for a lot of other things, and honestly, bracket pairs like (), [], {} are way too precious, imo, to squander on something like blocks. Parens () are exclusively for function application; square brackets [] are exclusively for indexing operations; curly braces {} are for type parameterization. The other option that C++ popularized the use of is <> — but that's syntactically sketchy since both < and > are valid by themselves. It makes parsing a complete nightmare — both for machines and, to a lesser extent, people. I wouldn't be completely averse to indentation-based blocking, but I'm not really a huge fan of it either. I'm cool with the way both Matlab and Ruby do it, which is using `end`. Could conceivably change, but relatively trivial syntactic alterations like this are a really low priority. What we have now works well and is familiar to both Ruby and Matlab programmers.