Learn how programming languages work, one tiny interpreter at a time.https://blog.tinyinterpreters.dev/https://blog.tinyinterpreters.dev/posts/recursion-without-recursive-bindings/https://blog.tinyinterpreters.dev/posts/recursion-without-recursive-bindings/Learn how to express recursion in FUN even though it lacks recursive bindings.Mon, 12 Oct 2026 06:20:00 GMThttps://blog.tinyinterpreters.dev/posts/fun-currying-free-variables/https://blog.tinyinterpreters.dev/posts/fun-currying-free-variables/Fix a subtle problem with currying and free variables by changing what FUN stores in a function value, uncovering closures along the way.Mon, 28 Sep 2026 03:30:00 GMThttps://blog.tinyinterpreters.dev/posts/fun-first-class-functions/https://blog.tinyinterpreters.dev/posts/fun-first-class-functions/Extend LET with first-class functions, then use currying and partial application to uncover an unexpected consequence of how function calls are evaluated.Mon, 21 Sep 2026 14:30:00 GMThttps://blog.tinyinterpreters.dev/posts/letdep/https://blog.tinyinterpreters.dev/posts/letdep/LETDEP gives multiple-binding let expressions dependency-ordered binding semantics: initializer dependencies determine the evaluation order, allowing forward references while rejecting duplicate names and cyclic bindings.Fri, 11 Sep 2026 09:00:00 GMThttps://blog.tinyinterpreters.dev/posts/letseq/https://blog.tinyinterpreters.dev/posts/letseq/LETSEQ gives multiple-binding let expressions sequential binding semantics: bindings are evaluated in source order, with each new binding becoming available to the ones that follow it.Thu, 10 Sep 2026 09:00:00 GMThttps://blog.tinyinterpreters.dev/posts/letpar/https://blog.tinyinterpreters.dev/posts/letpar/LETPAR gives multiple-binding let expressions parallel binding semantics: every initializer is evaluated in the incoming environment, so sibling bindings cannot see one another.Wed, 09 Sep 2026 09:00:00 GMThttps://blog.tinyinterpreters.dev/posts/multiple-binding-let-expressions/https://blog.tinyinterpreters.dev/posts/multiple-binding-let-expressions/Extend LET so a single let expression can contain multiple bindings, updating the grammar, AST, and parser before deciding what those bindings mean.Tue, 08 Sep 2026 09:00:00 GMThttps://blog.tinyinterpreters.dev/posts/let/https://blog.tinyinterpreters.dev/posts/let/LET extends VAR with let expressions, allowing programs to introduce local bindings and showing how environments determine their scope and support shadowing.Mon, 07 Sep 2026 12:30:00 GMThttps://blog.tinyinterpreters.dev/posts/var/https://blog.tinyinterpreters.dev/posts/var/VAR extends IF with variable expressions and environments, making evaluation depend on context as variable names are looked up in the current environment.Mon, 31 Aug 2026 11:55:00 GMThttps://blog.tinyinterpreters.dev/posts/if/https://blog.tinyinterpreters.dev/posts/if/IF extends ZERO with conditional expressions, using Boolean conditions to choose which of two branches to evaluate while leaving the other unevaluated.Mon, 24 Aug 2026 06:40:00 GMThttps://blog.tinyinterpreters.dev/posts/make-it-a-syntax-error/https://blog.tinyinterpreters.dev/posts/make-it-a-syntax-error/See how grammar and AST design in a tiny Elm interpreter can turn runtime type errors into syntax errors, simplify evaluation, and connect to GADTs.Thu, 20 Aug 2026 12:00:00 GMThttps://blog.tinyinterpreters.dev/posts/zero/https://blog.tinyinterpreters.dev/posts/zero/ZERO extends DIFF with the zero? predicate and Boolean values, then introduces runtime type errors for expressions that use values of the wrong type.Mon, 17 Aug 2026 07:40:00 GMThttps://blog.tinyinterpreters.dev/posts/lexeme-parsers-in-elm/https://blog.tinyinterpreters.dev/posts/lexeme-parsers-in-elm/Learn how lexeme parsers simplify whitespace handling in elm/parser by consuming trailing whitespace and keeping parsers close to the grammar.Fri, 14 Aug 2026 11:50:00 GMThttps://blog.tinyinterpreters.dev/posts/why-recursive-elm-parsers-need-parser-lazy/https://blog.tinyinterpreters.dev/posts/why-recursive-elm-parsers-need-parser-lazy/Learn why recursive Elm parsers create cyclic definitions, how Parser.lazy breaks the cycle, and when recursive parsers do and don't need it.Wed, 12 Aug 2026 12:50:00 GMThttps://blog.tinyinterpreters.dev/posts/diff/https://blog.tinyinterpreters.dev/posts/diff/DIFF extends CONST with difference expressions whose operands are themselves expressions, revealing the same recursive structure in the grammar, AST, parser, and evaluator.Mon, 10 Aug 2026 09:00:00 GMThttps://blog.tinyinterpreters.dev/posts/setting-up-a-reproducible-elm-interpreter-project-with-nix/https://blog.tinyinterpreters.dev/posts/setting-up-a-reproducible-elm-interpreter-project-with-nix/Set up a reproducible Elm interpreter project with a Nix flake, Elm tooling, helper commands, source and test structure, and grammar documentation.Thu, 06 Aug 2026 08:50:00 GMThttps://blog.tinyinterpreters.dev/posts/testing-an-elm-interpreter-with-elm-test/https://blog.tinyinterpreters.dev/posts/testing-an-elm-interpreter-with-elm-test/Learn how to test an Elm interpreter with elm-test at the lexer, parser, and interpreter boundaries, then extract a reusable testValue helper.Tue, 04 Aug 2026 07:50:00 GMThttps://blog.tinyinterpreters.dev/posts/const/https://blog.tinyinterpreters.dev/posts/const/CONST is a tiny Elm interpreter for non-negative integer constants, showing the path from source text through an AST to an evaluated value.Mon, 03 Aug 2026 05:00:00 GMT