Higher-Order Functions Using Environments

This lecture explores the transition from using substitutions to environments in the interpretation of higher-order functions, allowing for a more efficient and concise implementation. By defining an enum to include both integers and functions, the interpreter leverages the underlying language's first-class functions to support higher-order functions. The lecture demonstrates a metacircular approach, where the interpreter relies on the features of the underlying language to implement language features. Through examples of evaluating expressions, handling recursive functions, and implementing binary operations and conditionals, the lecture showcases how functions are used to represent syntactic objects, resulting in a compact and elegant interpreter.