# Life Arcs - Storybook Language Guide
Comprehensive documentation for the Storybook narrative simulation language

# Life Arcs

Life arcs are state machines that model how characters or other entities evolve over time. They define discrete states and the conditions under which an entity transitions between states. Life arcs capture character development, quest progress, relationship phases, and any other finite-state processes.

## What is a Life Arc?

A life arc is a finite state machine (FSM) composed of:

- States: Discrete phases or modes (e.g., “happy”, “angry”, “sleeping”)
- Transitions: Conditional edges between states (e.g., “when health < 20, go to ‘fleeing’”)
- On-enter actions: Field updates that occur when entering a state

    [State A] --condition--> [State B] --condition--> [State C]
        |                         |                       |
     on enter                  on enter                on enter
     (set fields)              (set fields)            (set fields)

Life arcs run continuously, evaluating transitions every tick and moving between states as conditions become true.

## Syntax

    <life-arc-decl> ::= "life_arc" <identifier> <body>

    <body> ::= "{" <prose-blocks>* <state>+ "}"

    <state> ::= "state" <identifier> "{" <state-body>* "}"

    <state-body> ::= <on-enter-block>
                   | <transition>
                   | <prose-block>

    <on-enter-block> ::= "on" "enter" "{" <field>+ "}"

    <transition> ::= "on" <expression> "->" <identifier>

    <prose-block> ::= "---" <identifier> <content> "---"

## States

A state represents a discrete phase in an entity’s lifecycle.

### Basic State

    life_arc SimpleArc {
        state idle {
            ---narrative
            The character is doing nothing, waiting for something to happen.
            ---
        }

        state active {
            ---narrative
            The character is engaged in their primary activity.
            ---
        }
    }

### State Names

State names are identifiers that must be unique within the life arc. Use descriptive names:

- Good: `idle`, `combat`, `sleeping`, `enlightened`
- Avoid: `state1`, `s`, `temp`

## On-Enter Actions

When entering a state, the `on enter` block updates entity fields.

### Syntax

    state state_name {
        on enter {
            EntityName.field_name: value
            EntityName.other_field: other_value
        }
    }

### Examples

    life_arc CharacterMood {
        state happy {
            on enter {
                Martha.emotional_state: "happy"
                Martha.energy: 100
            }
        }

        state tired {
            on enter {
                Martha.emotional_state: "exhausted"
                Martha.energy: 20
            }
        }
    }

### Field Update Semantics

- Target: `EntityName.field_name` must reference an existing character/entity
- Value: Any valid value type
- Effect: Field is set to the specified value when state is entered
- Timing: Happens immediately upon transition to the state

### Multiple Field Updates

    state exhausted_baker {
        on enter {
            Martha.energy: 0.1
            Martha.mood: "stressed"
            Martha.quality_output: 0.7
            Martha.needs_break: true
        }

        ---narrative
        After a sixteen-hour shift during the harvest festival,
        Martha's hands are shaking. She knows her bread quality is
        suffering and reluctantly steps away from the oven.
        ---
    }

## Transitions

Transitions define conditional edges between states. When a transition’s condition becomes true, the state machine moves to the target state.

### Syntax

    state source_state {
        on condition_expression -> target_state
        on another_condition -> another_target
    }

### Basic Transitions

    life_arc Combat {
        state fighting {
            on health < 20 -> fleeing
            on enemy_defeated -> victorious
        }

        state fleeing {
            on safe_distance_reached -> idle
        }

        state victorious {
            on celebration_complete -> idle
        }

        state idle {}
    }

### Expression Conditions

Transitions use the full expression language:

Comparisons:

    on health < 20 -> low_health
    on distance > 100 -> far_away
    on count == 0 -> empty

Boolean fields:

    on is_hostile -> combat
    on completed -> done
    on not ready -> waiting

Logical operators:

    on health < 20 and not has_potion -> desperate
    on is_day or is_lit -> visible

Complex conditions:

    on (health < 50 and enemy_count > 3) or surrounded -> retreat
    on forall e in enemies: e.defeated -> victory

### Multiple Transitions

A state can have multiple outgoing transitions:

    state monitoring {
        on status is "active" -> active_state
        on status is "inactive" -> inactive_state
        on status is "error" -> error_state
        on shutdown_requested -> shutting_down
    }

Evaluation order:

- Transitions are evaluated in declaration order (top to bottom)
- First transition with a true condition is taken
- If no conditions are true, state remains unchanged

### Self-Transitions

A state can transition to itself:

    state patrolling {
        on enemy_spotted -> combat
        on checkpoint_reached -> patrolling  // Reset patrol state
    }

## Complete Examples

### Elena’s Career Journey

    life_arc ElenaCareer {
        ---description
        Tracks Elena's progression from nervous apprentice to confident
        master baker. Each state represents a key phase of her career.
        ---

        state early_apprentice {
            on enter {
                Elena.skill_level: novice
                Elena.confidence: timid
            }

            on recipes_mastered > 5 -> growing_apprentice

            ---narrative
            Elena's hands shake as she measures flour. She checks the
            recipe three times before adding each ingredient. Martha
            patiently corrects her technique.
            ---
        }

        state growing_apprentice {
            on enter {
                Elena.skill_level: beginner
                Elena.confidence: uncertain
            }

            on recipes_mastered > 15 -> journeyman

            ---narrative
            The shaking stops. Elena can make basic breads without
            looking at the recipe. She still doubts herself but
            Martha's encouragement is taking root.
            ---
        }

        state journeyman {
            on enter {
                Elena.skill_level: intermediate
                Elena.confidence: growing
                Elena.can_work_independently: true
            }

            on recipes_mastered > 30 -> senior_journeyman

            ---narrative
            Elena runs the morning shift alone while Martha handles
            special orders. Customers start asking for "Elena's rolls."
            She begins experimenting with her own recipes.
            ---
        }

        state senior_journeyman {
            on enter {
                Elena.skill_level: advanced
                Elena.confidence: steady
            }

            on recipes_mastered > 50 -> master

            ---narrative
            Elena develops her signature recipe: rosemary olive bread
            that becomes the bakery's bestseller. She handles difficult
            customers with grace and trains new helpers.
            ---
        }

        state master {
            on enter {
                Elena.skill_level: master
                Elena.confidence: commanding
                Elena.can_teach: true
            }

            ---narrative
            Master Baker Elena. She has earned it. The guild acknowledges
            her mastery, and Martha beams with pride. Elena begins
            mentoring her own apprentice.
            ---
        }
    }

### Quest Progress

    life_arc HeroQuest {
        state not_started {
            on talked_to_elder -> received_quest
        }

        state received_quest {
            on enter {
                Hero.quest_active: true
                Hero.quest_step: 0
            }

            on found_first_artifact -> collecting
        }

        state collecting {
            on enter {
                Hero.quest_step: 1
            }

            on artifact_count == 3 -> returning
            on failed_trial -> failed
        }

        state returning {
            on enter {
                Hero.quest_step: 2
            }

            on reached_elder -> completed
        }

        state completed {
            on enter {
                Hero.quest_active: false
                Hero.quest_completed: true
                Hero.reputation: 100
            }

            ---narrative
            The hero returns triumphant, artifacts in hand. The elder
            bestows great rewards and the village celebrates.
            ---
        }

        state failed {
            on enter {
                Hero.quest_active: false
                Hero.quest_failed: true
            }

            on retry_accepted -> received_quest
        }
    }

### Name Checker (Equality Examples)

    life_arc NameCheck {
        state checking {
            on name is "Martha" -> found_martha
            on name is "Jane" -> found_jane
        }

        state found_martha {
            on ready -> checking
        }

        state found_jane {
            on ready -> checking
        }
    }

### Status Monitor

    life_arc StatusMonitor {
        state monitoring {
            on status is active -> active_state
            on status is inactive -> inactive_state
            on status is error -> error_state
        }

        state active_state {
            on enter {
                System.led_color: "green"
            }

            on status is inactive -> inactive_state
            on status is error -> error_state
        }

        state inactive_state {
            on enter {
                System.led_color: "yellow"
            }

            on status is active -> active_state
            on status is error -> error_state
        }

        state error_state {
            on enter {
                System.led_color: "red"
                System.alarm: true
            }

            on error_cleared -> monitoring
        }
    }

### Character Mood Swings

    life_arc MoodSwings {
        state neutral {
            on provoked -> angry
            on complimented -> happy
            on tired -> sleepy
        }

        state angry {
            on enter {
                Character.aggression: 0.9
                Character.willingness_to_talk: 0.1
            }

            on calmed_down -> neutral
            on escalated -> furious
        }

        state furious {
            on enter {
                Character.aggression: 1.0
                Character.will_attack: true
            }

            on timeout_elapsed -> angry
            on apologized_to -> neutral
        }

        state happy {
            on enter {
                Character.aggression: 0.0
                Character.willingness_to_talk: 1.0
                Character.gives_discounts: true
            }

            on insulted -> neutral
            on bored -> neutral
        }

        state sleepy {
            on enter {
                Character.responsiveness: 0.2
            }

            on woke_up -> neutral
            on fell_asleep -> sleeping
        }

        state sleeping {
            on enter {
                Character.responsiveness: 0.0
                Character.is_vulnerable: true
            }

            on woke_up -> neutral
        }
    }

## Execution Semantics

### Tick-Based Evaluation

Life arcs evaluate transitions every “tick” (typically once per frame):

1. Current state: Start in the current state
2. Evaluate transitions: Check each outgoing transition’s condition (in order)
3. First true transition: Take the first transition with a true condition
4. Enter new state: Execute the new state’s `on enter` block
5. Repeat next tick

### Transition Priority

When multiple transitions could fire, the first one in declaration order is taken:

    state combat {
        on health < 10 -> desperate       // Checked first
        on health < 50 -> defensive       // Checked second
        on surrounded -> retreat          // Checked third
    }

If health is 5, only `desperate` transition fires (even though `defensive` condition is also true).

### State Persistence

The current state persists across ticks until a transition fires.

    state waiting {
        on signal_received -> active
    }

The entity remains in `waiting` state indefinitely until `signal_received` becomes true.

### On-Enter Execution

`on enter` blocks execute once when entering the state, not every tick:

    state combat {
        on enter {
            Character.weapon_drawn: true  // Runs once when entering combat
        }
    }

## Validation Rules

1. At least one state: Life arc must contain at least one state
2. Unique state names: State names must be unique within the life arc
3. Valid transitions: Transition targets must reference defined states
4. No orphan states: All states should be reachable (warning, not error)
5. Expression validity: Transition conditions must be well-formed expressions
6. Field targets: On-enter field updates must reference valid entities/fields
7. No cyclic immediate transitions: Avoid transitions that fire immediately in a loop

## Design Patterns

### 1. Hub-and-Spoke

A central “hub” state with transitions to specialized states:

    life_arc HubPattern {
        state idle {
            on combat_triggered -> combat
            on quest_accepted -> questing
            on entered_shop -> shopping
        }

        state combat {
            on combat_ended -> idle
        }

        state questing {
            on quest_completed -> idle
        }

        state shopping {
            on left_shop -> idle
        }
    }

### 2. Linear Progression

States form a linear sequence (quests, tutorials):

    life_arc Tutorial {
        state intro {
            on clicked_start -> movement
        }

        state movement {
            on moved_forward -> combat
        }

        state combat {
            on defeated_enemy -> inventory
        }

        state inventory {
            on opened_inventory -> complete
        }

        state complete {}
    }

### 3. Cyclic States

States form a cycle (day/night, seasons):

    life_arc DayNightCycle {
        state dawn {
            on hour >= 8 -> day
        }

        state day {
            on hour >= 18 -> dusk
        }

        state dusk {
            on hour >= 20 -> night
        }

        state night {
            on hour >= 6 -> dawn
        }
    }

### 4. Hierarchical (Simulated)

Use multiple life arcs for hierarchical state:

    // Top-level life arc
    life_arc CharacterState {
        state alive {
            on health <= 0 -> dead
        }

        state dead {}
    }

    // Nested life arc (only active when alive)
    life_arc CombatState {
        state idle {
            on enemy_nearby -> combat
        }

        state combat {
            on enemy_defeated -> idle
        }
    }

## Best Practices

### 1. Use Descriptive State Names

Avoid:

    state s1 { ... }
    state s2 { ... }

Prefer:

    state waiting_for_player { ... }
    state engaged_in_combat { ... }

### 2. Add Narrative Prose Blocks

    state master_baker {
        ---narrative
        Master Baker Elena. She has earned it. The guild acknowledges
        her mastery, and Martha beams with pride. Elena begins
        mentoring her own apprentice.
        ---
    }

### 3. Order Transitions by Priority

    state health_check {
        on health <= 0 -> dead          // Most urgent
        on health < 20 -> critical      // Very urgent
        on health < 50 -> wounded       // Moderate
    }

### 4. Avoid Orphan States

Ensure all states are reachable from the initial state.

Avoid:

    life_arc Broken {
        state start {
            on ready -> middle
        }

        state middle {
            on done -> end
        }

        state unreachable {}  // No transition leads here!

        state end {}
    }

### 5. Use On-Enter for State Initialization

    state combat {
        on enter {
            Character.weapon_drawn: true
            Character.combat_stance: "aggressive"
            Character.target: nearest_enemy
        }
    }

## Cross-References

- Characters - Characters can have associated life arcs
- Expression Language - Transition condition syntax
- Value Types - On-enter field value types
- Validation Rules - Life arc validation constraints

## Related Concepts

- Finite State Machines (FSM): Life arcs are FSMs
- Character development: Track character growth over time
- Quest states: Model quest progression
- Mood systems: Model emotional states
- Lifecycle modeling: Birth, growth, aging, death