Can you create a language interpreter?
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In the past four weeks, I've been traveling a lot, which gave me many sleepless nights to kill. I used this time to revisit the blog "(How to Write a (Lisp) Interpreter (in Python))" (). This blog elegantly outlines the implementation of a Turing Complete LISP-style language in just 145 lines of Python code, reminding us that 'small is beautiful'. A programming language is a formal language that provides a set of instructions for communication with computers. Code in a programming language is merely a character stream for a computer, which it needs to tokenize according to the language's syntactical delimiters. It then parses these tokens into an expression understood by the language's interpreter or compiler - this expression is represented as an Abstract Syntax Tree (AST) in memory. In the interpretive language implemented by lispy, the AST is fed into an evaluation function, which interprets the AST's semantic meaning and executes it. The steps involve (1) tokenization (2) parsing into an AST expression (3) semantic execution of the expression. Let's delve into the essential constructs of a programming language as demonstrated in lispy: 1. Syntax: The rules that define correctly structured programs in the language. In lispy, this is handled by tokenization and parsing. 2. Semantics: The meanings of syntactic constructs, i.e., the actions the computer takes when executing a program. In lispy, the evaluation function interprets and executes the semantics of the AST. 3. Data Types: The types of values a program can process. Lispy supports integers, floating-point numbers, symbols, lists, and functions. 4. Control Structures: These dictate the program's control flow. Key structures include conditional statements (like `if`), loop constructs (implemented in lispy as recursive calls from procedures), and functions or procedures. 5. Abstraction Mechanisms: These make it possible to write reusable code, decoupled from specific systems or datasets. Procedures serve as lispy's primary abstraction mechanisms. 6. Paradigms: Most languages are designed around paradigms that guide the organization and structuring of code. Lispy adheres to the functional programming paradigm. Many new college graduates often lack a basic understanding of how a programming language is implemented – I was in the same boat when I first graduated. If you find yourself in a similar position, I highly recommend studying the language explanation and implementation at .