feature: adds support for Quantity hyperoperation at level 0

Author: bjacobgordon

NumberSystems/Sources/NumberSystems/Hyperoperable.swift

@@ -0,0 +1,17 @@
+public protocol Hyperoperable: Equatable, Operable {
+    mutating func hyperoperateUpon(
+        atLevel givenLevel: Self,
+        by givenOperametrum: Self
+    )
+}
+
+extension Hyperoperable {
+    public func hyperoperatedUpon(
+        atLevel givenLevel: Self,
+        by givenOperametrum: Self
+    ) -> Self {
+        var operatum = self
+        operatum.hyperoperateUpon(atLevel: givenLevel, by: givenOperametrum)
+        return operatum
+    }
+}

NumberSystems/Sources/NumberSystems/Quantity.swift

@@ -34,7 +34,7 @@ extension Quantity: Equatable {
     }
 }
 
-extension Quantity: Operable {
+extension Quantity: Hyperoperable {
     public mutating func succeed() {
         let newElement = self.embodiment.first ?? Quantity.standardEmbodyingElement
         self.embodiment.append(newElement)
@@ -45,6 +45,15 @@ extension Quantity: Operable {
 
         self.embodiment.removeLast()
     }
+    
+    public mutating func hyperoperateUpon(
+        atLevel givenLevel: Quantity,
+        by givenOperametrum: Quantity
+    ) {
+        if (givenLevel == Quantity.none) { return self.succeed() }
+
+        fatalError("Higher-level operations not yet defined")
+    }
 }
 
 extension String {

NumberSystems/Tests/NumberSystemsTests/QuantityTests.swift

@@ -73,3 +73,19 @@ func predecessorOfQuantity(_ givenCount: Int) async throws {
     let  precededQuantity = operativeQuantity.predecessor
     #expect(precededCount.represents(precededQuantity))
 }
+
+@Test("Operatrum-agnostic characteristics of level 0 hyperoperation", arguments: [
+    Quantity(""  )!,
+    Quantity("|" )!,
+    Quantity("||")!
+])
+func hyperoperationAtLevel0(_ givenOperametrum: Quantity) async throws {
+    let zero =  0.asQuantity
+    let ten  = 10.asQuantity
+
+    let eleven =    ten.hyperoperatedUpon(atLevel: zero, by: givenOperametrum)
+    let twelve = eleven.hyperoperatedUpon(atLevel: zero, by: givenOperametrum)
+
+    #expect(11.represents(eleven))
+    #expect(12.represents(twelve))
+}