Support dictionary literals using infix operator (#40)

Sources/AnyExpression.swift

@@ -401,7 +401,24 @@ public struct AnyExpression: CustomStringConvertible {
                         }
                     }
                 case .function("[]", _):
-                    return { box.store($0.map(box.load)) }
+                    return { args in
+                        let args = args.map(box.load)
+                        let keyVals = args.compactMap({ $0 as? Dictionary<AnyHashable, Any>.Element })
+                        return box.store(
+                            args.isEmpty || args.count != keyVals.count
+                            ? args
+                            : keyVals.reduce(into: [AnyHashable: Any](), { $0[$1.key] = $1.value })
+                        )
+                    }
+                case .infix(":"):
+                    return { args in
+                        switch (box.load(args[0]), box.load(args[1])) {
+                        case let (lhs as AnyHashable, rhs):
+                            return box.store(Dictionary<AnyHashable, Any>.Element(key: lhs, value: rhs))
+                        case let (lhs, rhs):
+                            throw Error.typeMismatch(symbol, [lhs, rhs])
+                        }
+                    }
                 case let .variable(name):
                     guard let string = unwrapString(name) else {
                         return { _ in throw Error.undefinedSymbol(symbol) }
@@ -608,6 +625,8 @@ extension AnyExpression.Error {
             }
         case .infix("==") where types.count == 2 && types[0] == types[1]:
             return .message("Arguments for \(symbol) must conform to the Hashable protocol")
+        case .infix(":") where types.count == 2 && !(args[0] is AnyHashable):
+            return .message("First argument for \(symbol) must conform to the Hashable protocol")
         case _ where types.count == 1:
             return .message("Argument of type \(types[0]) is not compatible with \(symbol)")
         default:

Tests/AnyExpressionTests.swift

@@ -398,6 +398,48 @@ class AnyExpressionTests: XCTestCase {
         }
     }
 
+    func testStringDictionaryLiteral() {
+        let expression = AnyExpression("['a': 1, 'b': 2.5, 'c': 3]")
+        XCTAssertEqual(try expression.evaluate(), ["a": 1, "b": 2.5, "c": 3])
+    }
+
+    func testDoubleDictionaryLiteral() {
+        let expression = AnyExpression("[1.5: false, 2.0: nil, 3.5: true]")
+        XCTAssertEqual(try expression.evaluate(), [1.5: false, 2.0: nil, 3.5: true])
+    }
+
+    func testIntDictionaryLiteral() {
+        let expression = AnyExpression("[1: 'f', 2: 'e', 3: 'd']")
+        XCTAssertEqual(try expression.evaluate(), [1: "f", 2: "e", 3: "d"])
+    }
+
+    func testDictionaryLiteralWithNonHashableKey() {
+        let expression = AnyExpression("[nil: false]")
+        XCTAssertThrowsError(try expression.evaluate() as Any) { error in
+            XCTAssertEqual(error as? Expression.Error, .typeMismatch(.infix(":"), [nil as Any? as Any, false]))
+        }
+    }
+
+    func testSubscriptStringDictionaryLiteralWithString() {
+        let expression = AnyExpression("['a': 1, 'b': 2.5, 'c': 3]['c']")
+        XCTAssertEqual(try expression.evaluate(), 3)
+    }
+
+    func testSubscriptDoubleDictionaryLiteralWithInt() {
+        let expression = AnyExpression("[1.5: false, 2.0: nil, 3.5: true][2]")
+        XCTAssertEqual(try expression.evaluate(), Optional<Bool>.none)
+    }
+
+    func testSubscriptIntDictionaryLiteralWithDouble() {
+        let expression = AnyExpression("[1: 'f', 2: 'e', 3: 'd'][1.0]")
+        XCTAssertEqual(try expression.evaluate(), "f")
+    }
+
+    func testSubscriptDictionaryLiteralWithNonexistentKey() {
+        let expression = AnyExpression("[1: 'f', 2: 'e', 3: 'd']['d']")
+        XCTAssertEqual(try expression.evaluate(), Optional<String>.none)
+    }
+
     // MARK: Ranges
 
     func testClosedIntRange() {