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Task/Fibonacci-sequence/Ra/fibonacci-sequence.ra

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+class FibonacciSequence
+	**Prints the nth fibonacci number**
+	
+	on start
+		
+		args := program arguments
+		
+		if args empty
+			print .fibonacci(8)
+		
+		else
+			
+			try
+				print .fibonacci(integer.parse(args[0]))
+			
+			catch FormatException
+				print to Console.error made !, "Input must be an integer"
+				exit program with error code
+			
+			catch OverflowException
+				print to Console.error made !, "Number too large"
+				exit program with error code
+	
+	define fibonacci(n as integer) as integer is shared
+		**Returns the nth fibonacci number**
+		
+		test
+			assert fibonacci(0) = 0
+			assert fibonacci(1) = 1
+			assert fibonacci(2) = 1
+			assert fibonacci(3) = 2
+			assert fibonacci(4) = 3
+			assert fibonacci(5) = 5
+			assert fibonacci(6) = 8
+			assert fibonacci(7) = 13
+			assert fibonacci(8) = 21
+
+		
+		body
+			a, b := 0, 1
+		
+			for n
+				a, b := b, a + b
+		
+			return a