Lambda the Ultimate

Page 4 of the lecture notes from Mitch Wand's first Principles of Programming Languages lecture:

When looking at a language, we will always ask four questions. As we proceed through the course, we will ask these questions in more and more sophisticated ways; I’ll show some of these subquestions now, even though we haven’t yet covered enough to understand what they mean:

1. What are the values in the language?
   • What are the values manipulated by the language, and what operations on those values are represented in the language?
   • What are the expressed and denoted values in the language?
   • What are the types in the language?
2. What are the scoping rules of the language?
   • How are variables bound? How are they used?
   • What variables are in scope where?
3. What are the effects in the language?
   • Are there side-effects in the language?
   • Can execution of programs have effects in the world?
   • Can execution of programs have effects on other programs?
   • Can execution of a program fail to terminate?
   • Are there non-local control effects in the language?
4. What are the static properties of the language?
   • What can we predict about the behavior of a program without knowing the run-time values?
   • How can we analyze a program to predict this behavior?

What do you consider the fundamental properties of a programming language?