AttaLambda: a language where types and data are made of untyped lambdas

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49699477

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HN

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AttaLambda: a language where types and data are made of untyped lambdas

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attalambda.com

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Sept. 14, 2026

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44

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0.8381180223285486

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Fetched at

Sept. 18, 2026, 5:02 p.m.

Updated at

Sept. 18, 2026, 5:02 p.m.

Description

I made a programming language!I call it AttaLambda.The idea is this: a usable Lisp-shaped language where all the meaningful computation is done in untyped lambda calculus. Logic, arithmetic, data structures, control flow, even the types — all untyped lambdas. A small, explicit Racket layer sits at the boundary to handle the outside world, plus some macros for syntactic sugar.This is its story:A couple years ago, I wanted to play with untyped lambda calculus and go beyond where tutorials usually stop. They show booleans, numbers, arithmetic, maybe the Y-combinator — and then stop. I wanted them to keep going.So I started a project called All The Lambdas. Using Racket set to lazy, I used only one Racket construct for actual computation — lambda — and built integers, rationals, lists, binary digit-list number encodings, search algorithms, and more.Then I found Functional Programming Through Lambda Calculus by Greg Michaelson. In it, Michaelson sketches the bones of a language built in untyped lambda calculus, including a type system where typed objects are themselves pair functions containing a type tag and value.I found that intriguing and implemented and extended the idea, still entirely with untyped lambdas. I don't have a background in programming language theory, so I was figuring it out as I went.Then I stopped tinkering with it for a while.Recently I came back and thought: why not turn this into a real usable language with the help of coding agents? I reused most of All The Lambdas as the foundation.Thus AttaLambda was born.Some additional details:* Rat, its number type, uses binary digit-list encodings instead of Church numerals, so numbers scale with their number of binary digits rather than their value* errors are lambda-encoded values, not Racket exceptions, and propagate through the language like ordinary data* the Racket host only performs irreducibly external operations; even things like HTTP parsing, routing, and response construction stay in the pure lambda world* recursion uses lambda-calculus recursion: no loops or true self-reference, just the Y-combinator underneath* automated purity checks catch accidental cheating, like native computation leaking into the pure parts* syntax like multi-argument lambdas, let, cond, and list is just macro sugar that reduces to unary lambdas and applicationA couple code examples: (short of print, every single thing here reduces to unary untyped lambdas)Factorial: #lang attalambda (rec factorial n = (cond ((eq n 0) 1) (else (mult n (factorial (sub n 1)))))) (print (factorial 10)) Which prints: 3628800 Or an exact harmonic sum: #lang attalambda (print (reduce add 0 (map (lambda (n) (unwrap-ok (div 1 n))) (range 1 8)))) Which prints exactly: 363/140 As far as I know, no programming language combines all these features: Michaelson-style type tags built from untyped lambdas, exact rationals backed by binary digit lists, errors as lambda values, and real-world programs where almost all computation stays inside the lambda core. None of those pieces are individually new, but I don't know of another language combining them this way.Download: https://github.com/kserrec/attalambda/releases/tag/v0.7.0Code: https://github.com/kserrec/attalambdaOriginal All The Lambdas: https://github.com/kserrec/all_the_lambdas

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