Integrating built-ins with control structures
Control structures are usually bigger things than expressions, such as loops. They are often associated with novel programming language semantics or new scopes that specialized computations can occur in. Control structures provide a context that a statement (often, this is a compound statement consisting of a whole block of code) is executed in. This can be whether (or how many times) it is executed, what associated data the code is to be applied to, or even what semantics the operators should be interpreted with. Sometimes, these control structures are explicitly and solely used for your new operators or built-in functions, but often, the interactions are implicit byproducts of the problem solving that your language enables.
Whether a given block of code is executed, selecting which of several to execute or executing code repeatedly are the most traditional control structures, such as if statements and loops. The most likely opportunities...
