2: The Fireplace DSL

Action Sequences

Hearthstone defines sequences of actions that can happen at certain times. For example, a Battlecry will happen when a card was played from the hand. A Deathrattle will happen when a card with the DEATHRATTLE tag dies.

Those sequences can be defined in two ways. The recommended way is using the Fireplace DSL. Sequences which are too complex to be implemented using the DSL can be implemented as callables, which return an iterable of actions. An Action Sequence refers to an argument which can be an iterable of actions, or a callable that returns an iterable of actions.

The full Action reference is available here.

Card Pickers

When generating a card dynamically is needed, such as summoning a random minion of some sort, card pickers can declaratively describe how the card should be picked.

Random pickers

There is a set of RandomPickers available, all building on top of fireplace.dsl.RandomCardPicker:

• RandomCard()
• RandomCollectible()
• RandomMinion()
• RandomSpell()
• RandomWeapon()
• RandomSparePart()

Each of those pickers, as well as the base one, can take filters. For example, to give the controller a random Dream Card, you would do:

Give(CONTROLLER, RandomCard(card_class=CardClass.DREAM))

To summon a random legendary minion that costs 5 mana, you would do:

Summon(CONTROLLER, RandomMinion(cost=5, rarity=Rarity.LEGENDARY))

Copy()

Copy() is a picker that takes a selector as argument, and returns copies of the arguments it's given. It can also be OR'd, in order to provide a fallback when the selector comes up empty:

Summon(CONTROLLER, Copy(RANDOM_ENEMY_MINION) | "CS2_231")

Card Evaluators

When lazily evaluating a certain condition is required for a card's functionality, an Evaluator can be written. An Evaluator implements the evaluate(source, game) method, which returns True or False, depending on its given conditions.

The following Evaluators are implemented:

• Dead(selector): Returns True if every target matching the selector is dead.
• Find(selector, count): Returns True if the selector evaluates to at least count entities. count defaults to 1.

An evaluator has an optional "then" clause, and an optional "else" clause. To describe those clauses, use the & (binary and) and | (binary or) operators, respectively. For example, to implement the Kill Command effect:

Find(FRIENDLY_MINIONS + BEAST) & Hit(TARGET, 5) | Hit(TARGET, 3)

Lazy Numbers

The DSL supports some lazy numbers, which evaluate when the action runs. They can be used to multiply action or affect the amounts of other actions.

There are two LazyNum implemented: Count() and Attr()

Count() takes a selector argument and will evaluate to how many matches there are. For example, to draw a card for every enemy minion:

Draw(CONTROLLER) * Count(ENEMY_MINIONS)

Attr() takes a selector and a tag GameTag argument and will evaluate the sum of the tags matching the selector. For example, to hit a target with the total armor of your hero:

Hit(TARGET, Attr(FRIENDLY_HERO, GameTag.ARMOR))

When performing some operations on LazyNums, they turn into a LazyNumEvaluator, which lets them behave as an evaluator. For example, Light of the Naaru is implemented as such:

play = Heal(TARGET, 3), (Attr(TARGET, GameTag.DAMAGE) >= 1) & Summon(CONTROLLER, "EX1_001")

Note that the parentheses are required due to Python's operator precedence.