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storybook/docs/reference/13-life-arcs.md

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release: Storybook v0.2.0 - Major syntax and features update BREAKING CHANGES: - Relationship syntax now requires blocks for all participants - Removed self/other perspective blocks from relationships - Replaced 'guard' keyword with 'if' for behavior tree decorators Language Features: - Add tree-sitter grammar with improved if/condition disambiguation - Add comprehensive tutorial and reference documentation - Add SBIR v0.2.0 binary format specification - Add resource linking system for behaviors and schedules - Add year-long schedule patterns (day, season, recurrence) - Add behavior tree enhancements (named nodes, decorators) Documentation: - Complete tutorial series (9 chapters) with baker family examples - Complete reference documentation for all language features - SBIR v0.2.0 specification with binary format details - Added locations and institutions documentation Examples: - Convert all examples to baker family scenario - Add comprehensive working examples Tooling: - Zed extension with LSP integration - Tree-sitter grammar for syntax highlighting - Build scripts and development tools Version Updates: - Main package: 0.1.0 → 0.2.0 - Tree-sitter grammar: 0.1.0 → 0.2.0 - Zed extension: 0.1.0 → 0.2.0 - Storybook editor: 0.1.0 → 0.2.0
2026-02-13 21:52:03 +00:00
# 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
```bnf
<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
```storybook
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
```storybook
state state_name {
on enter {
EntityName.field_name: value
EntityName.other_field: other_value
}
}
```
### Examples
```storybook
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](./18-value-types.md)
- **Effect**: Field is set to the specified value when state is entered
- **Timing**: Happens immediately upon transition to the state
### Multiple Field Updates
```storybook
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
```storybook
state source_state {
on condition_expression -> target_state
on another_condition -> another_target
}
```
### Basic Transitions
```storybook
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](./17-expressions.md):
**Comparisons:**
```storybook
on health < 20 -> low_health
on distance > 100 -> far_away
on count == 0 -> empty
```
**Boolean fields:**
```storybook
on is_hostile -> combat
on completed -> done
on not ready -> waiting
```
**Logical operators:**
```storybook
on health < 20 and not has_potion -> desperate
on is_day or is_lit -> visible
```
**Complex conditions:**
```storybook
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:
```storybook
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:
```storybook
state patrolling {
on enemy_spotted -> combat
on checkpoint_reached -> patrolling // Reset patrol state
}
```
## Complete Examples
### Elena's Career Journey
```storybook
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
```storybook
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)
```storybook
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
```storybook
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
```storybook
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:
```storybook
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.
```storybook
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:
```storybook
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:
```storybook
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):
```storybook
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):
```storybook
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:
```storybook
// 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:**
```storybook
state s1 { ... }
state s2 { ... }
```
**Prefer:**
```storybook
state waiting_for_player { ... }
state engaged_in_combat { ... }
```
### 2. Add Narrative Prose Blocks
```storybook
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
```storybook
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:**
```storybook
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
```storybook
state combat {
on enter {
Character.weapon_drawn: true
Character.combat_stance: "aggressive"
Character.target: nearest_enemy
}
}
```
## Cross-References
- [Characters](./10-characters.md) - Characters can have associated life arcs
- [Expression Language](./17-expressions.md) - Transition condition syntax
- [Value Types](./18-value-types.md) - On-enter field value types
- [Validation Rules](./19-validation.md) - 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
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