Playground

The playground runs the same tree-walking interpreter that powers nex run — compiled to JavaScript via Scala.js and loaded lazily into the page on first click. Single-file programs only; the playground bypasses the module loader so there’s no filesystem dependency, no Node assumption.

Click Run to execute. The first run loads the interpreter bundle (~1.8 MB minified, ~400 KB over compression), so it takes a second; subsequent runs reuse the cached bundle and finish in milliseconds.

Hello

Arrays and HOFs

Complex numbers

A tiny FFT (recursive, N = 4)

Limitations

• Single-file programs only. The playground bypasses the module loader; import won’t work here. Use multiple defs in the same buffer.
• No file I/O, no stdin. Output is whatever print(...) produces.
• No nex compile path. This runs the interpreter; the AOT compile path needs clang and is JVM-only.
• Real precision. Numbers print with Java’s Double.toString shortest-round-trip here (matching the JVM interpreter exactly). The AOT binary uses an iterative shortest-round-trip helper that converges to the same byte sequence — see the Verification chapter for the parity contract.

A polished editor (CodeMirror + Nex syntax highlighting) is on the roadmap; the current textarea is intentionally minimal to validate the experience first.