Some would say top-level blocks returning the last value in the block is an anti-pattern, because functions which aren't meant to return a value end up leaking the value of the last thing called in the function, which might be another function, which called another function. Or it might be in various branches of an 'if', which aren't being examined for being an acceptable return value.

Perl does this, (like ECMAScript's 'do'), and while it's usefully concise sometimes, for API-level functions I think it's poor to accidentally leak values to the caller, that should never escape. The safe way to deal with this is an explicit void return at the end of API functions, but that's ugly and hard to remember.

I think JavaScript made the right choice in requiring explicit return from functions with blocks to return a value, with 'undefined' returned if nothing explicit is. Accidents are avoided.

Rust has taken an interesting approach of requiring a return type to be specified, which stops accidental leaks at least. Respect.

Rust will also only return the last expression in a block if it doesn't end in a semicolon. This can be a bit subtle when you're reading a long function, but combined with explicitly specified return types its hard to mess up while writing code. Because of the choice about that semicolon, its an explicit choice whether you want a block to evaluate into that expression or not. And for functions you can always just use an explicit return statement if you want anyway.

This will ignore the last result and return Nil instead:

    sub foo ( $_ --> Nil ) {…}

If you specify a type instead, it only enforces that the result is of that type.

Keep in mind this is only a stage 0 proposal, and thus is not really part of the language. This is how statements behave when entered into the repl, e.g. the browser dev console.

Ruby has an if/else structure like the Rust/Lisp thing, as well. Tasty.