Aven

Aven is an experimental typed glue language: Hindley-Milner inference with row-polymorphic records/variants and literal types, a Zig-style comptime layer, and a type-safe host/script boundary, built tooling-first (diagnostics, formatter, and LSP grew ahead of the runtime). Programs run today through a tree-walking evaluator with a host-provided platform (files, stdio, HTTP, JSON, structured logging).

cargo run -p aven -- check examples/hello.av        # parse + name + type checks
cargo run -p aven -- check --format json file.av    # machine-readable diagnostics
cargo run -p aven -- check --timings file.av        # phase timings
cargo run -p aven -- run examples/maps.av           # execute against the host
cargo run -p aven -- run tool.av -- --verbose       # pass arguments to a script
cargo run -p aven -- fmt --check examples/hello.av  # formatter
cargo run -p aven -- explain parse.unclosed-delimiter
cargo run -p aven -- tokens file.av                 # lexer debug
cargo run -p aven -- layout file.av                 # layout debug
cargo run -p aven -- lsp                            # language server (stdio)

Scripts receive args: Array(Text) and programName: Text (the script basename). Interpreter options precede the script path. A final Int expression selects the process exit code (0–255); use writeLine to print an integer. Other final values are displayed, and @Err entries exit with status 1.

For an executable script, use #!/usr/bin/env -S aven run -- (or an absolute interpreter path followed by run --). This separator comes before the script path so every script argument, including a leading --, is preserved. In an explicit aven run tool.av -- ... invocation, the first post-path -- is the interpreter separator; a second -- is passed to the script.

• crates/aven-core — source spans, structured diagnostics, the diagnostic code registry and explanations
• crates/aven-parser — lexer, layout pass, unified-grammar parser (types and patterns are ordinary expression terms), declarations, name analysis
• crates/aven-fmt — source formatter
• crates/aven-check — semantic checking: annotation lowering, HM inference, row polymorphism, literal types, the comptime evaluator
• crates/aven-compiler — compiler database: snapshots, timings, declaration-keyed artifacts and invalidation
• crates/aven-eval — tree-walking evaluator and runtime values
• crates/aven-host — the typed host boundary: value+type registration, typed-fn adapter, host comptime resolvers, file/stream/HTTP/JSON capabilities
• crates/aven-lsp — language server implementation
• crates/aven-cli — the aven command-line interface

examples/*.av are executable documentation, locked by integration tests: every example must check cleanly, and hermetic ones also run with asserted output.

• docs/tooling-first-plan.md — the milestone plan and its current queue (the authoritative "what's next")
• docs/cli-library.md — std/cli: typed arguments, commands, help and shell completions
• Editor setup lives in editors/