Use differentiation pipeline in demo

src/bin/demo.rs

@@ -1,20 +1,12 @@
-use deriv::Expression;
-use deriv::Evaluator;
 use deriv::Repl;
-
-struct DummyEvaluator;
-
-impl Evaluator for DummyEvaluator {
-	type Expr = Expression;
-	type Error = std::io::Error;
-
-	fn eval(&mut self, input: Self::Expr) -> Result<Self::Expr, Self::Error> {
-		Ok(input)
-	}
-}
+use deriv::eval;
 
 fn main() -> std::io::Result<()> {
-	let mut repl = Repl::new(
-		std::io::stdin(), std::io::stdout(), DummyEvaluator {});
+	let eval = deriv::pipeline!(
+		eval::Normaliser::new(),
+		eval::Differentiator::new('x'),
+		eval::ConstFolder::new(),
+		eval::Simplifier::new());
+	let mut repl = Repl::new(std::io::stdin(), std::io::stdout(), eval);
 	repl.run()
 }