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 in which specialized computations occur. Control structures provide a context in which a statement (often, this is a compound statement consisting of a whole block of code) is executed. This can be whether (or how many times) it is executed, on what associated data the code is computing, or even what semantics to apply during the evaluation of the operators.
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 blocks to execute or executing code repeatedly are the most traditional control structures, such as if statements and loops. The most...
