Why Lisp?

Lisp (1958) is the second-oldest high-level programming language still in use (after Fortran). It pioneered:

• Garbage collection
• First-class functions
• Recursion as primary control flow
• REPL (read-eval-print loop)
• Code-as-data (homoiconicity)
• Macros (compile-time code generation)

Modern descendants: Common Lisp, Scheme, Clojure, Racket, Emacs Lisp.

Why is Lisp's syntax all parentheses?

(+ 1 2 3)              ; 6
(* (+ 1 2) (- 5 3))    ; 6
(if (> x 0) "positive" "non-positive")

Each (...) is a list. The first element is the operation; the rest are arguments. EVERYTHING is this structure.

The benefit: code IS data. A program is a list. You can manipulate it like data, then evaluate. This makes macros trivial — your macro is a function that takes code (lists) and returns code (lists).

Hard to find another language where this is true. Most languages have separate syntactic forms (statements, expressions, declarations); Lisp has one form (the list). Simpler to parse, simpler to manipulate.

We'll build a tiny Lisp/Scheme in this course. It'll have arithmetic, conditionals, functions, closures, recursion, and macros. ~200 lines of Python.