In which scenario is an interpreter always required?

An interpreter is always required in scenarios where translation and execution occur simultaneously, specifically when processing a single line of code at a time. In this context, an interpreter takes the high-level code, analyzes it, and executes it immediately, rather than compiling the entire program into machine code beforehand. This approach allows for immediate feedback and easier debugging for developers, as errors can be identified as soon as they occur rather than after the full compilation.

In contrast, running compiled programs does not require an interpreter since they have already been translated into machine code before execution. High-level languages can be executed using either compilers or interpreters, so while interpreters are often used with high-level languages, they are not exclusively required. Optimizing machine code, however, involves refining the translated code for performance, which is a different process from interpretation. Therefore, the requirement for an interpreter is uniquely tied to the real-time, line-by-line execution characteristic described.