Return Stack

"Where you've been is where you can go back to."

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What Is It?

Return Stack treats navigation history as a first-class continuation — a stack of saved positions you can manipulate like browser history or a call stack.

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The Metaphor

Programming	Browser	MOOLLM
Call stack	History	Return stack
Return address	Back button	Previous room
Stack frame	Tab	Room context
Push	Navigate	ENTER
Pop	Back	BACK

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Commands

Command	Effect
ENTER room	Push current room, enter new one
BACK	Pop stack, return to previous room
FORWARD	Redo after BACK (if available)
HISTORY	Show the stack
BOOKMARK	Save current position
GOTO bookmark	Jump to saved position
STACK	Show all open "tabs" (parallel stacks)
FORK	Create new tab from current position

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Example Session

> ENTER workshop
[Stack: lobby]

> ENTER storage
[Stack: lobby → workshop]

> ENTER archive
[Stack: lobby → workshop → storage]

> BACK
Returning to storage...
[Stack: lobby → workshop]

> BACK
Returning to workshop...
[Stack: lobby]

> HISTORY
  1. lobby (start)
  2. workshop
  3. storage
  4. archive ← furthest

Current: workshop (position 2)

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Bookmarks

Save positions for later:

> BOOKMARK "interesting-spot"
Bookmarked: workshop as "interesting-spot"

> ENTER research
> ENTER data-room
> ENTER sub-analysis
[Deep in the hierarchy]

> GOTO interesting-spot
Returning to workshop...
[Stack cleared, at bookmark]

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Forking (Tabs)

Create parallel exploration paths:

> FORK
Created new tab from workshop.
Tab 1: lobby → workshop
Tab 2: workshop (active) ←

> ENTER experiment-A
[Tab 2: workshop → experiment-A]

> STACK
Tab 1: lobby → workshop
Tab 2: workshop → experiment-A ←

> TAB 1
Switching to Tab 1...
[Now at workshop via tab 1]

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As Continuation

The return stack IS a continuation:

# Stored in character's pocket
return_stack:
  - path: "./lobby"
    context: {examining: "welcome-sign"}
  - path: "./workshop"
    context: {crafting: "blueprint-v2"}
  - path: "./storage"
    context: {searching: "rare-materials"}

# Current position
current: "./archive"
context: {reading: "old-records"}

When you BACK, you don't just return to the room — you restore the context you had there.

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Portable Journey

The stack travels with you:

> INVENT
Inventory:
  - notebook
  - pen
  - return_stack: [lobby → workshop → storage]

You can:

• Save your journey to a file
• Share it with others
• Replay someone else's exploration
• Branch from any point in their journey

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HyperCard Heritage

HyperCard had:

• Stacks of cards
• "Go back" button
• Breadcrumb trail
• Bookmarks

MOOLLM extends this:

• Rooms as cards
• BACK command
• Return stack as data
• Bookmarks as saved positions
• FORK for parallel exploration

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Implementation

# character.yml
name: explorer
location: ./archive

navigation:
  return_stack:
    - room: ./lobby
      entered: "2024-01-15T10:00:00"
    - room: ./workshop
      entered: "2024-01-15T10:05:00"
      context:
        active_task: "crafting"
    - room: ./storage
      entered: "2024-01-15T10:15:00"

  bookmarks:
    interesting-spot:
      room: ./workshop
      context: {task: "blueprint-review"}
    start:
      room: ./lobby

  forward_stack: []  # After BACK, stores where you came from

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Dynamic Deoptimization

The Self programming language (source of our prototype inheritance) pioneered dynamic deoptimization: aggressively inlining code for performance, then reconstructing the "logical" call stack on demand when debugging.

The LLM does this naturally for narrative:

Self	MOOLLM
Inlined bytecode	Flattened conversation
Deoptimized frames	Reconstructed causality
Breakpoint trigger	"How did we get here?"
Stack trace	Causal chain from evidence

The stack isn't explicitly maintained, but it's recoverable.

How It Works

When you ask for history, the LLM examines:

evidence_sources:
  - session_log: "Append-only narrative trail"
  - room_state: "Accumulated changes"
  - character_location: "Current position"
  - file_timestamps: "Order of modifications"
  - chat_context: "Recent decisions"

And synthesizes a virtual stack trace:

Deduced navigation:
1. lobby (start)
2. workshop (examining blueprints)
3. storage (found locked chest)
4. workshop (returned for key) ← BACK
5. storage (unlocked chest)
6. archive (following map) ← current

This is introspection without instrumentation — the same insight that made Self's debugger magical.

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Dovetails With

• Action Queue — The complement: stack = past, queue = future
• Room — What you're navigating between
• Coherence Engine — Tracks navigation state
• Adventure — Narrative exploration
• Session Log — Records the journey
• Prototype — Self language heritage
• Debugging — Stack traces on demand

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Protocol Symbols

RETURN-STACK      — Navigation history as data
BACK / FORWARD    — Stack manipulation
BOOKMARK / GOTO   — Saved positions
FORK              — Parallel exploration
HYPERCARD-HIERARCHY — The room/card model

See: PROTOCOLS.yml