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, 0 insertions, 59 deletions

diff --git a/repcore/src/grammar.rs b/repcore/src/grammar.rs
deleted file mode 100644
index ee9f033..0000000
--- a/repcore/src/grammar.rs
+++ /dev/null
@@ -1,59 +0,0 @@
-//! This file implements the extected behaviours of grammars.
-
-// NOTE: We shall first start with a parser that works at the level of
-// characters.  The purpose is to first experiment with the workings
-// and the performance of the algorithms, before optimising by using
-// regular expressions to classify inputs into tokens.  In other
-// words, the current focus is not on the optimisations, whereas
-// scanners are for optimisations only, so to speak.
-
-/// The type of a terminal.
-///
-/// For the time being this is a wrapper around a string, but in the
-/// future it may hold more information of scanners.
-pub struct Terminal {
-    // If we want to use scanners, per chance add them as a new field
-    // here.
-    name: String,
-}
-
-impl Terminal {
-    /// Create a terminal with the given name.
-    #[inline]
-    pub fn new(name: String) -> Self {
-        Self { name }
-    }
-
-    /// Return the name of the terminal.
-    #[inline]
-    pub fn name(&self) -> &str {
-        &self.name
-    }
-}
-
-/// The type of a non-terminal.
-///
-/// This is just a wrapper around a string.
-pub struct Nonterminal(String);
-
-impl Nonterminal {
-    /// Return the name of the nonterminal.
-    ///
-    /// Just to improve readability.
-    #[inline]
-    pub fn name(&self) -> &str {
-        &self.0
-    }
-}
-
-/// The type of a terminal or a non-terminal.
-///
-/// Only an index is stored here.  Actual data are stored in two other
-/// arrays.
-#[derive(Debug, Hash, Eq, PartialEq, Clone, Copy, Ord, PartialOrd)]
-pub enum TNT {
-    /// Terminal variant
-    Ter(usize),
-    /// Nonterminal variant
-    Non(usize),
-}