The code is written the same way it is logically structured. `let` takes 1+ arguments: a set of symbol bindings to values, and 0 or more additional statements which can use those symbols. In the example you are replying to, `bar-x` and `quux-y` are symbols whose values are set to the result of `(bar x)` and `(quux y)`. After the binding statement, additional statements can follow. If the bindings aren't kept together in a `[]` or `()` you can't tell them apart from the code within the `let`.