Lamdu is a graphical, projectional IDE for a custom statically typed functional language (Lamdu Calculus). Users edit a structured AST through a text-like GUI — not raw text — with automatic parenthesization, type-directed hole completion, live type annotations, and evaluation results displayed inline. Programs are persisted in a versioned RocksDB-backed store (Revision.Deltum) that supports undo/redo and branching, and are exchangeable via a schema-versioned JSON format (currently migration chain at version 16) plus a JavaScript export format. The system is a single monolithic Haskell desktop application: entry point src/main/Lamdu/Main.hs exposes CLI commands (DeleteDb, Undo, Import, Export, Editor); the GUI layer (Lamdu.GUI.*, built on the Momentu widget framework over GLFW) converts keystrokes and menu selections into editing transactions on the versioned store.