Add interface for enumerating over sequences.

source/coral.cpp

@@ -495,6 +495,35 @@ export namespace coral {
 		 */
 		virtual expected<usize, io_error> write(slice<u8 const> const & data) = 0;
 	};
+
+	/**
+	 * Sequence enumeration interface.
+	 */
+	template<typename type> struct enumerator {
+		virtual ~enumerator() {}
+
+		/**
+		 * Returns the last-enumerated value.
+		 *
+		 * *Note*: calling this function before first having recieved a `true` value from [enumerate] will result in
+		 * implementation-defined behaviour.
+		 */
+		virtual type value() = 0;
+
+		/**
+		 * Attempts to retrieve the next file path in the file tree, returning true if another value was retrieved or
+		 * `false` if there are no more values to be enumerated over.
+		 *
+		 * ```cpp
+		 * while (sequence.enumerate()) {
+		 *   do_thing(sequence.value());
+		 * }
+		 * ```
+		 *
+		 * The enumerated value may be accessed through [value].
+		 */
+		virtual bool enumerate() = 0;
+	}
 }
 
 // Input/output operations.