Nelumbo is a logic meta-language for specifying declarative languages. You define your DSL's syntax and semantics - the semantics in pure logic - and every construct is live on the very next line.
Why Nelumbo
Language workbenches let you define structure and notation. Nelumbo goes further: you also define what your language means, as inference rules - and the language runs while you are still writing it.
One pattern line - `Boolean ::= <Person> likes <Person>` -
and the new notation is first-class syntax, with IDE support included.
Meaning is written as inference rules over honest three-valued logic. Logic is the medium, not the target: you write your domain, the engine does the reasoning.
Nelumbo executes immediately: a construct defined on line n
is available from line n+1 on. No generators, no compile
step, no deployment loop.
Everything a language workbench gives you, plus executable semantics - with live IDE support in the browser, VS Code, IntelliJ and Eclipse, and an MCP server for AI assistants.
See it grow
This is real Nelumbo: one line declares new syntax, one rule gives it meaning in logic, and the query at the bottom already speaks the new language - the editor verifies the expected answer live. Try it yourself in the tutorial; no install needed.