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Vera

Vera is a statically typed, purely functional programming language designed for large language models to write. It uses typed slot references (`@T.n`) instead of variable names, requires contracts (preconditions, postconditions, effect declarations) on every function, and compiles to WebAssembly. Programs run at the command line via wasmtime or in the browser.

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Authority: 45 reach 0 · trust 5 · quality 25 · freshness 15
Tier: listed
llms.txt: https://veralang.dev/llms.txt
llms-full.txt: https://veralang.dev/llms-full.txt
Sections: 7
Links: 37
Size: 7602 bytes
Country: United States Hosting inference
Hosting country: United States Hosting inference
Country evidence: No published address evidence collected yet
Categories: AI and machine learning
For agents: Informational: content or services for people, nothing to operate
First seen: 2026-10-27T10:04:55.510Z
Last checked: 2026-10-27T10:04:56.201Z
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The beginning of the file, from our validated copy saved 2026-10-27T10:04:55.517Z. Cached copy · Source on veralang.dev

# Vera

> Vera is a statically typed, purely functional programming language designed for large language models to write. It uses typed slot references (`@T.n`) instead of variable names, requires contracts (preconditions, postconditions, effect declarations) on every function, and compiles to WebAssembly. Programs run at the command line via wasmtime or in the browser.

Vera uses De Bruijn indexing for bindings: `@Int.0` is the most recent `Int` binding, `@Int.1` the one before. There are no variable names. Contracts are mandatory — every function must declare `requires(...)`, `ensures(...)`, and `effects(...)`, and every recursive function a `decreases(...)` measure or the `Diverge` effect. The Z3 SMT solver verifies contracts statically where possible; every contract is also compiled as a runtime check where code generation can express it, and most of what can be neither proved nor guarded is disclosed (#1695 tracks the contracts that are not). All side effects (IO, Http, HttpServer, State, Exceptions, Async, Inference, DB, Random, Diverge) are tracked in the type system via algebraic effects.

The reference compiler is written in Python; its releases are listed on [GitHub](https://github.com/aallan/vera/releases) and [PyPI](https://pypi.org/project/veralang/). Install the `veralang` distribution from PyPI, or use `pip install -e ".[dev]"` from the repository — the recommended route for agents, since it includes the examples, conformance programs and specification the language reference teaches from.

## Homepage

- [Vera](https://veralang.dev/index.md): Markdown companion to veralang.dev — project overview, thesis, design principles, key features, quick install, and links to the full documentation set.

## Language Reference

- [SKILL.md](https://veralang.dev/SKILL.md): Complete language reference — syntax, types, slot references, contracts, effects, built-in functions, common mistakes, and working examples. This is the primary document for writing Vera code.

## Quick Start

- [AGENTS.md](https://raw.githubusercontent.com/aallan/vera/main/AGENTS.md): Instructions for AI agents — workflow, commands, error handling, and essential rules for writing correct Vera.
- [FAQ](https://raw.githubusercontent.com/aallan/vera/main/FAQ.md): Design rationale — why no variable names, what gets verified, comparison to Dafny/Lean/Koka, research citations.
- [TOOLCHAIN.md](https://raw.githubusercontent.com/aallan/vera/main/TOOLCHAIN.md): The CLI cookbook — driving the toolchain to write, verify, test, run, and debug Vera, and the `builtins`/`effects`/`errors` introspection commands.
- [DE_BRUIJN.md](https://raw.githubusercontent.com/aallan/vera/main/DE_BRUIJN.md): Typed slot references in depth — worked examples and the commutative-operations trap.
- [ENVIRONMENT.md](https://raw.githubusercontent.com/aallan/vera/main/ENVIRONMENT.md): Every `VERA_*` environment variable — provider keys, runtime knobs, and debug flags.
- [KNOWN_ISSUES.md](https://raw.githubuserco
…

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