renaming core to chain and some other changes

Some changes:

- The core crate is renamed to "chain".

- The crate "viz" is added, which will provide layered graph drawing
  algorithms.

- A function is added to convert from a grammar to the regular
  language of its left-linear closures.

- A function is added to convert from a nondeterministic finite
  automaton to its "null" closure.  A null closure is the same
  automaton with edges added, as if some edges are "null".  Whether an
  edge is null is determined by a function.
  Combined with the previous change, we can convert a grammar to the
  regular language of the null closure of its left-linear closures.

---

Now it remains to test more grammars and add an Atom trait, before
finishing the part about compilations.

1 files changed, 25 insertions, 0 deletions

diff --git a/chain/src/lib.rs b/chain/src/lib.rs
new file mode 100644
index 0000000..0ec4d4c
--- /dev/null
+++ b/chain/src/lib.rs
@@ -0,0 +1,25 @@
+//! This package implements the core algorithm of the entire
+//! workspace: parsing with derivatives by means of chain rule and
+//! regular nulling languages.
+//!
+//! Since I shall not name my crate "core" to avoid collisions with
+//! the Rust's own core, I decided to name this crate after what I
+//! think is the essence of this algorithm, the chain-rule for
+//! derivatives of languages.
+
+pub mod grammar;
+
+pub fn add(left: usize, right: usize) -> usize {
+    left + right
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn it_works() {
+        let result = add(2, 2);
+        assert_eq!(result, 4);
+    }
+}