A small programming language where everything is pass-by-value
This is a hobby project of mine that I started a few years ago to learn about programming language implementation. It was created 95% without AI, although a few recent commits include code from Gemini CLI. I started out following Crafting Interpreters, but gradually branched off that until I had almost nothing left in common. Tech stack: Rust, Cranelift (JIT compilation), LALRPOP (parser). Original title: "A small programming language where everything is a value" (edited based on comments)
A small programming language where everything is pass-by-value launched on January 25, 2026 with 91 votes, #383 of 14,585 launches that month and more than 95% of that year's launches.
In plain words
This is a hobby programming language built in Rust that implements pass-by-value semantics throughout. The creator developed it over several years to learn language implementation, initially following Crafting Interpreters before diverging significantly. It uses Cranelift for JIT compilation and LALRPOP for parsing. Designed for programmers interested in language design, it represents a learning project created almost entirely without AI assistance.
written from the facts on this page · September 2026
From the sources
A simple interpreted programming language where everything is pass-by-value - Jcparkyn/herd
Herd is a simple interpreted programming language where everything is a value. Disclaimer: This is a hobby language, and you probably shouldn't use it for anything important. In Herd, everything is pass-by-value, including lists and dicts. This means that when you pass a list or dict to a function, you can guarantee that the function won't modify your copy . You can modify variables locally just like you would in an imperative language, but there will never be any side-effects on other copies of the value. var foo = { a : 1 }; var bar = foo; // make a copy of foo set bar.a = 2 ; // modify bar (makes a copy) println foo.a bar.a; // prints 1 2 How does it work? All reference types in Herd…from github.com
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