xpr-lang

A sandboxed expression language with near-byte-identical runtimes in TypeScript, Python, and Go.

3 runtimes 601 conformance tests 71 built-ins

npm: @xpr-lang/xpr
PyPI: xpr-lang
Go: github.com/xpr-lang/xpr-go

Source Homepage

TypeScript
Python
Go
Parser theory
EBNF
VitePress
Vite
CodeMirror

Sandboxed expression language with a formal EBNF specification — no I/O, no loops, no side effects — with parsers and evaluators in TypeScript, Python, and Go held near-byte-identical across 601 conformance tests.
Shipped to npm + PyPI + Go modules with VitePress docs, an interactive playground (Vite + CodeMirror), and 71 built-in functions.

The XPR language specification page covering literals and operators, alongside a contents list running from arrow functions and let bindings through the pipe operator, regex functions and negative array indexing. — The spec is the source of truth all three runtimes are tested against.

Why I built it

Most expression languages for data pipelines are either too unsafe (full JavaScript with eval), too primitive (cron-style templates), or runtime- specific (you write your pipeline expression once for Python, again for Go). xpr-lang fills the gap: one syntax, three implementations, formal guarantees about safety, and conformance-tested behavior across runtimes.

Architecture highlights

Single source of truth: the EBNF grammar in xpr-lang/xpr is the authoritative spec. Each runtime parses to the same AST shape.
YAML conformance suite: 601 test cases driving identical behavior across TS/Python/Go, plus 71 built-in functions. CI on every PR.
Zero I/O surface: no file, network, or OS access; no import, no eval, no loops. Safe to evaluate untrusted user expressions.
Familiar syntax: arrow functions, pipe operator, optional chaining, destructuring, regex literals — if you know modern JS/Python, you can read xpr-lang.
Three runtimes: TypeScript (@xpr-lang/xpr), Python (xpr-lang), Go (github.com/xpr-lang/xpr-go).