add-combinator

name	add-combinator
description	Add a card-authoring combinator to MtgPure.Model.Combinators in mtg-pure. Use when a card definition needs DSL vocabulary that doesn't exist yet (a new effect/cost/requirement/ability helper), or when card code is reaching for a raw Recursive constructor because no combinator wraps it. Explains the thin-wrapper + As* coercion pattern and how combinators relate to the Recursive DSL.

Add a card-authoring combinator

MtgPure.Model.Combinators is the surface vocabulary card definitions are written in (see the big import block at the top of Cards.hs). Combinators are thin wrappers over the raw MtgPure.Model.Recursive constructors, existing so cards read like Magic and so multiple concrete object types can be accepted uniformly.

House rule (from CODING_STYLE.md): card definitions use a combinator wherever one exists rather than a raw constructor. So when a card needs a constructor that isn't yet wrapped, add the wrapper here.

Do not build here (see memory mtg-pure-no-builds).

Before adding: check what exists

• Is there already a combinator that does this? (Grep the export list.)
• Does the underlying Recursive constructor exist? If the constructor itself is missing, that's a DSL change — see the model-round-trip skill first (adding a constructor touches Show/Ord/ConsIndex), then come back and wrap it.

The pattern

Most combinators are a one-liner: the constructor, possibly post-composed with an As* coercion. Examples from the file:

manaCost :: (ToManaCost a) => a -> Cost
manaCost = ManaCost . toManaCost

destroy :: (AsPermanent ot) => ZO 'ZBattlefield ot -> Effect 'OneShot
destroy = Destroy . asPermanent

dealDamage ::
  (AsDamageSource source, AsCreaturePlayerPlaneswalker target, AsDamage damage, IsZO zone OTNDamageSource) =>
  ZO zone source -> ZO 'ZBattlefield target -> damage -> Effect 'OneShot
dealDamage source target = DealDamage (asDamageSource source) (asCreaturePlayerPlaneswalker target) . asDamage

is :: (IsZone zone, CoAny ot) => ZO zone ot -> Requirement zone ot
is = Is

Conventions:

• Pick the right result layer the card author needs to produce: Effect 'OneShot / Effect 'Continuous, Cost, Requirement zone ot, Condition, Elect s el ot, StaticAbility/ActivatedAbility/... Match the constructor's own result type.
• Prefer an As* coercion class (AsDamage, AsPermanent, AsAny, AsSpell, AsCreaturePlayerPlaneswalker, …) on arguments so the combinator accepts any convertible object type, exactly like the neighbors. If you need a coercion that doesn't exist, add a small As* class here following the existing ones rather than forcing a concrete type.
• Keep the same constraint style (IsZO zone ot, CoPermanent ot, CoAny ot, IsOTN ot) the surrounding combinators use.
• InstanceSigs, \case, explicit lambdas — same house style as everywhere.

Wire it up

1. Add the name to the MtgPure.Model.Combinators export list. The list mixes plain values and As*(..)/class exports; keep it roughly alphabetized like the existing entries (leading commas).
2. Import whatever Recursive constructor / type you now reference into this module's import safe MtgPure.Model.Recursive ( ... ) block (alphabetized).
3. In Cards.hs, add the new name to the big import safe MtgPure.Model.Combinators ( ... ) block (alphabetized) so cards can use it.

Checklist

• Confirmed no existing combinator covers it, and the Recursive constructor exists
• Wrapper defined with explicit type, right result layer, As* coercions on args
• Exported from Combinators (alphabetized)
• Needed Recursive names imported into Combinators (alphabetized)
• Added to the Combinators import block in Cards.hs (alphabetized)