painless-java-engine

Painless → Java execution engine for document mutation.

Overview

This project is a demo implementation of a Painless-like scripting engine, built to showcase the full processing pipeline:

• Tokenization (lexical analysis)
• Parsing into an Abstract Syntax Tree (AST)
• Compilation into executable commands
• Runtime execution

The implementation demonstrates how a simple scripting language can be designed and executed end-to-end.

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Supported Painless Subset

The current implementation supports a practical subset of Painless, including:

• variable declarations and assignments
• if / if-else / block statements / return
• path access via dot notation (ctx._source.status)
• map-style bracket access (ctx._source['status'])
• symbolic map/list initialization ([:], [], ['k': v], [1,2,3])
• literals: null, string, integer, decimal, boolean
• binary operators: logical, equality, comparison, arithmetic
• unary operators: !, unary + / -, prefix/postfix ++ and --
• function calls, method calls, casts, and instanceof

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Scope

This is a demo / showcase project, focused on:

• language modeling
• AST design
• execution flow

It is not a full implementation of OpenSearch Painless.

Example

if (ctx._source.status == null) {
  ctx._source.status = 'READY';
}

return ctx._source.status;