Nelumbo: A new logic meta-language

Nelumbo has launched as a logic meta-language for specifying declarative languages, in which developers define a DSL's syntax and semantics as inference rules over three-valued logic and every construct becomes available on the next line, with no generators, compile step or deployment loop. Nelumbo ships live IDE support in the browser, VS Code, IntelliJ and Eclipse, plus an MCP server for AI assistants, and a single pattern line such as `Boolean ::= <Person> likes <Person>` makes new notation first-class syntax. A no-install tutorial lets users try the language directly.

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 https://nelumbo.nl/tutorial.html ; no install needed.