LambdaHandler

type LambdaHandler<T = any> = (ctx: LambdaCtx) => T;

A LambdaHandler is a function that takes a LambdaCtx context object as its parameter and returns a value of the specified type T. It's a core concept in NarraLeaf for creating dynamic, context-aware logic that can access game state, player data, and other runtime information.

Overview

LambdaHandlers are used throughout NarraLeaf to provide dynamic behavior based on the current game state. They allow you to write functions that can:

Access player data and game state
Perform calculations based on current context
Create conditional logic that responds to runtime conditions
Generate dynamic content based on game progress

Basic Usage

In Conditions

// Simple boolean condition
Condition.If(
    (ctx) => ctx.$("player").get("coin") >= 10,
    [/* actions when player has 10+ coins */]
)
 
// Complex condition with multiple checks
Condition.If(
    (ctx) => {
        const player = ctx.$("player");
        const hasKey = player.get("key") === true;
        const hasEnoughCoins = player.get("coin") >= 50;
        return hasKey && hasEnoughCoins;
    },
    [/* actions when both conditions are met */]
)

In Menu Choices

// Dynamic menu choice visibility
menu.choose("Go to the shop", [/* actions */])
    .hideIf((ctx) => ctx.$("player").get("shop_unlocked") !== true);
 
// Dynamic menu choice state
menu.choose("Buy item", [/* actions */])
    .disableIf((ctx) => ctx.$("player").get("coin") < 100);

In Persistent Data Comparisons

// Compare with dynamic values
persis.equals("player_id", (ctx) => ctx.storable.getNamespace("player").get("player_id"));

Context Object (LambdaCtx)

The ctx parameter provides access to the current game context:

interface LambdaCtx extends ScriptCtx {
    gameState: GameState;    // Current game state
    game: Game;              // Game instance
    liveGame: LiveGame;      // Live game session
    storable: Storable;      // Data storage system
    $: NamespaceGetter;      // Namespace accessor function
}

Accessing Data

// Access player data
(ctx) => ctx.$("player").get("health")
 
// Access game state
(ctx) => ctx.gameState.currentScene?.id
 
// Access stored data
(ctx) => ctx.storable.getNamespace("inventory").get("items")
 
// Access live game data
(ctx) => ctx.liveGame.getCurrentTime()

Advanced Examples

Complex Conditional Logic

// Multi-condition check
const canEnterDungeon = (ctx) => {
    const player = ctx.$("player");
    const inventory = ctx.$("inventory");
    
    const hasKey = inventory.get("dungeon_key") === true;
    const hasWeapon = inventory.get("weapon") !== null;
    const hasEnoughHealth = player.get("health") >= 50;
    
    return hasKey && hasWeapon && hasEnoughHealth;
};
 
Condition.If(canEnterDungeon, [
    // Allow dungeon entry
]);

Type Safety

LambdaHandlers support full TypeScript type inference:

// Explicitly typed handler
const getPlayerName: LambdaHandler<string> = (ctx) => {
    return ctx.$("player").get("name") || "Unknown Player";
};
 
// Type-safe data access
const getPlayerLevel: LambdaHandler<number> = (ctx) => {
    return ctx.$("player").get("level") || 1;
};

For more information about the context object, see LambdaCtx and ScriptCtx.

LambdaCtx LiveGameEvent