Implement std::fmt::Display for eval::Error

src/eval.rs

@@ -21,3 +21,11 @@ pub trait Evaluator {
 
 	fn eval(&mut self, input: Self::Expr) -> Result<Self::Expr, Self::Error>;
 }
+
+impl std::fmt::Display for Error {
+	fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+		write!(f, "{}", match self {
+			Error::UnsupportedExpression => "Unsupported expression",
+		})
+	}
+}