From 186d94ff1744db28f1ccf96a820e88a875ac22df Mon Sep 17 00:00:00 2001
From: Alexander Ignatov <yalishanda@abv.bg>
Date: Thu, 16 Dec 2021 12:26:50 +0200
Subject: [PATCH] Add membership function and continuous set basic defs

---
 Sources/FuzzyKit/ContinuousFuzzySet.swift     | 27 +++++++++++++++++
 Sources/FuzzyKit/MembershipFunction.swift     | 29 +++++++++++++++++++
 .../ContinuousFuzzySetTests.swift             |  6 ++++
 .../MembershipFunctionTests.swift             | 13 +++++++++
 4 files changed, 75 insertions(+)
 create mode 100644 Sources/FuzzyKit/ContinuousFuzzySet.swift
 create mode 100644 Sources/FuzzyKit/MembershipFunction.swift
 create mode 100644 Tests/FuzzyKitTests/ContinuousFuzzySetTests.swift
 create mode 100644 Tests/FuzzyKitTests/MembershipFunctionTests.swift

diff --git a/Sources/FuzzyKit/ContinuousFuzzySet.swift b/Sources/FuzzyKit/ContinuousFuzzySet.swift
new file mode 100644
index 0000000..e310bf6
--- /dev/null
+++ b/Sources/FuzzyKit/ContinuousFuzzySet.swift
@@ -0,0 +1,27 @@
+public struct ContinuousFuzzySet: FuzzySet {
+    public typealias Element = Double
+    
+    private let membershipFunction: MembershipFunction
+    
+    public init(membershipFunction: MembershipFunction) {
+        self.membershipFunction = membershipFunction
+    }
+    
+    public init(membershipFunction: @escaping (Element) -> Grade) {
+        self.membershipFunction = MembershipFunction(membershipFunction)
+    }
+    
+    public func grade(forElement element: Element) -> Grade {
+        membershipFunction(element)
+    }
+}
+
+public extension ContinuousFuzzySet {
+    static var empty: Self {
+        .init(membershipFunction: .zero)
+    }
+    
+    static var universe: Self {
+        .init(membershipFunction: .one)
+    }
+}
diff --git a/Sources/FuzzyKit/MembershipFunction.swift b/Sources/FuzzyKit/MembershipFunction.swift
new file mode 100644
index 0000000..3dcc8a5
--- /dev/null
+++ b/Sources/FuzzyKit/MembershipFunction.swift
@@ -0,0 +1,29 @@
+public struct MembershipFunction {
+    
+    private let function: (Double) -> Double
+    
+    public init(_ function: @escaping (Double) -> Grade) {
+        self.function = function
+    }
+    
+    public func callAsFunction(_ x: Double) -> Double {
+        function(x)
+    }
+}
+
+/// Common membership functions
+public extension MembershipFunction {
+    static var zero: Self {
+        .init { _ in 0.0 }
+    }
+    
+    static var one: Self {
+        .init { _ in 1.0 }
+    }
+    
+    static func fuzzySingleton(_ a: Double) -> Self {
+        .init { $0 == a ? 1.0 : 0.0 }
+    }
+    
+    // TODO: Add more
+}
diff --git a/Tests/FuzzyKitTests/ContinuousFuzzySetTests.swift b/Tests/FuzzyKitTests/ContinuousFuzzySetTests.swift
new file mode 100644
index 0000000..bf375e0
--- /dev/null
+++ b/Tests/FuzzyKitTests/ContinuousFuzzySetTests.swift
@@ -0,0 +1,6 @@
+import XCTest
+import FuzzyKit
+
+final class ContinuousFuzzySetTests: XCTestCase {
+    // TODO
+}
diff --git a/Tests/FuzzyKitTests/MembershipFunctionTests.swift b/Tests/FuzzyKitTests/MembershipFunctionTests.swift
new file mode 100644
index 0000000..9dda954
--- /dev/null
+++ b/Tests/FuzzyKitTests/MembershipFunctionTests.swift
@@ -0,0 +1,13 @@
+import XCTest
+import FuzzyKit
+
+final class MembershipFunctionTests: XCTestCase {
+    func test_isCallable() throws {
+        let sut = MembershipFunction.one
+        let x = 1.0
+        
+        let result = sut(x)
+        
+        XCTAssertEqual(result, x)
+    }
+}