Which type of program executes instructions written in a programming language?

The answer is an interpreter, which directly executes the instructions written in a programming language without the need for a prior compilation step. It translates high-level programming code into machine code on-the-fly, allowing for immediate execution of the code line by line. This makes it particularly useful for scripting, rapid prototyping, and situations where immediate feedback is valuable.

Interpreters are essential in environments where developers need to test small snippets of code or run scripts interactively. The immediate execution capability allows developers to see the results of their code without the extra step of compiling, which can streamline the development process.

Other types of programs serve different functions: a compiler converts the entire program into machine code before execution, which can lead to faster overall performance but does not provide immediate feedback like an interpreter. A debugger is used for finding and fixing bugs in code rather than executing code, and an assembler translates assembly language (a low-level language) into machine code, which is a different layer of programming. Understanding these distinctions helps clarify why the interpreter is the type of program that executes instructions written in a programming language directly.