Lisp
A language family dating to 1958, whose programs are written as the list structures they manipulate.
27 steps across 1 tours, from the basics to complete programs.
The tours
- First released
- 1958
- Created by
- John McCarthy
- Typing
- Dynamic and strong; everything is an expression, code is a list
- Snippets target
- ANSI CL (SBCL)
- File extensions
- .lisp, .lsp, .cl
What it is for
Lisp is the second-oldest high-level language still in use, and the source most others borrowed from: garbage collection, conditionals as expressions, first-class functions, and the interactive REPL all appeared here first. The dialect these seeds drill is Common Lisp — the big, standardized branch that powers Google's flight-search engine (ITA), Grammarly's core, and decades of research code that never needed a rewrite.
What keeps working Lispers loyal is the workflow: a running image you redefine one function at a time, restarts that let you fix an error and continue instead of restarting, and CLOS, an object system with multiple dispatch that still outclasses most of what came after. Programs are built from the inside out, live, with the compiler (SBCL compiles to native code) a keystroke away.
The parentheses everyone jokes about are the point: code is written directly as the list structure the language itself manipulates, which is why macros — functions that write code — are ordinary Lisp instead of a separate template language. Learning to read the tree instead of the punctuation is the skill, and it transfers to every expression-oriented language you will touch.
Where it came from
John McCarthy specified Lisp at MIT in 1958 as a mathematical notation for computing with symbolic expressions, and Steve Russell realized eval could simply be implemented — turning a paper into an interpreter. Through the 1960s and 70s Lisp was the language of artificial intelligence research, growing dialects at every lab: Maclisp, Interlisp, Scheme, and the Lisp machines that put it in hardware.
Common Lisp was the 1984 truce that merged the feuding dialects into one deliberately large language, becoming an ANSI standard in 1994 — the first object-oriented language to get one, thanks to CLOS. The AI winter took the Lisp machine companies down, but the standard meant the language itself survived on stock hardware, with free native-code compilers like CMUCL and later SBCL.
The standard has not changed since 1994, and Lispers count that as a feature: code from the 90s runs today, and the library ecosystem grew around Quicklisp instead of language churn. Meanwhile the family kept branching — Scheme in teaching, Racket in research, Clojure on the JVM — and every language that added lambdas, REPLs, or macros re-imported a piece of 1958.
What it is like to type
Lisp typing is parenthesis cadence: open-paren bursts, a defun or let head, then arguments separated by single spaces, then the closing run of parens — often four or five in a row. There are almost no infix operators or commas to slow you down, but the *earmuffs*, the #' function quote, and format's ~ directives keep the right hand honest. Indentation carries the structure your eyes read, so the two-space body indent must land exactly.
27 steps across 1 tours, from the basics to complete programs.