1 files changed, 46 insertions, 0 deletions
diff --git a/chain/src/default.rs b/chain/src/default.rs
new file mode 100644
index 0000000..e04be9f
--- /dev/null
+++ b/chain/src/default.rs
@@ -0,0 +1,46 @@
+//! This file provides a default implementation of the
+//! [`Chain`][crate::Chain] trait.
+//!
+//! The reason for using a trait is that I might want to experiment
+//! with different implementation ideas in the future, and this
+//! modular design makes that easy.
+
+use super::*;
+use core::fmt::Display;
+
+/// The errors related to taking derivatives by chain rule.
+#[derive(Debug)]
+pub enum Error {
+    /// An invalid situation happens.
+    Invalid,
+}
+
+impl Display for Error {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            Self::Invalid => write!(f, "invalid"),
+        }
+    }
+}
+
+impl std::error::Error for Error {}
+
+/// A default implementation for the [`Chain`] trait.
+#[derive(Debug, Clone, Default)]
+pub struct DefaultChain {}
+
+impl Chain for DefaultChain {
+    type Error = Error;
+
+    fn unit() -> Self {
+        todo!()
+    }
+
+    fn chain(&mut self, _t: usize) {
+        todo!()
+    }
+
+    fn epsilon(&self) -> bool {
+        todo!()
+    }
+}