3 files changed, 124 insertions, 0 deletions
diff --git a/repcore/src/grammar.rs b/repcore/src/grammar.rs
new file mode 100644
index 0000000..ee9f033
--- /dev/null
+++ b/repcore/src/grammar.rs
@@ -0,0 +1,59 @@
+//! 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),
+}
diff --git a/repcore/src/lib.rs b/repcore/src/lib.rs
index 7d12d9a..589b61c 100644
--- a/repcore/src/lib.rs
+++ b/repcore/src/lib.rs
@@ -1,3 +1,9 @@
+//! This package implements the core algorithm of the entire
+//! workspace: parsing with derivatives by means of regular nulling
+//! languages.
+
+pub mod grammar;
+
 pub fn add(left: usize, right: usize) -> usize {
     left + right
 }
diff --git a/repcore/src/plan.org b/repcore/src/plan.org
new file mode 100644
index 0000000..13c2ee0
--- /dev/null
+++ b/repcore/src/plan.org
@@ -0,0 +1,59 @@
+#+TITLE: Plan of the package
+#+AUTHOR: Durand
+#+DATE: <2022-11-18 Ven 19:57>
+
+* Atomic Languages
+
+This describes the behaviours of atomic languages.  The atomic
+language consists of the null closure of any non-terminal symbol in
+the grammar, and their deriavtives by terminals and non-terminal.
+
+* Derivative Languages
+
+This is the main driving device of the algorithm.  Basically, the
+algorithm works by taking successive derivatives, according to the
+input symbol.  At each step, we calculate the derivative language.  In
+this process, we also compute some semiring value and store in a
+carrier.  The end result of the algorithm is the final semiring
+value.
+
+If one wants simply to determine if the input string belongs to the
+grammar, one chooses the semiring to be the field with two elements,
+the boolean field.  If one wants to find how many ways are there to
+derive a given input string, then one uses the semiring of natural
+numbers instead.  If one wants, moreover, to find all the possible
+ways to derive a particular input string, then one can use the
+free semiring on the set of terminals and non-terminals of the
+grammar.  Here the free semiring is the left-adjoint functor to the
+forgetful functor from the category of semirings to the category of
+sets.
+
+To be more specific, the free semiring on a set is given by sets of
+sequences of elements in the set.  The addition of the semiring is the
+set union operation, and the multiplication is taking the respective
+concatenations.
+
+** Semirings
+
+So we need a module to define the behaviours of semirings, and provide
+some common semirings implementations.  Then in the main driving force
+we can freely substitute different semirings, according to the
+particular needs.
+
+** Languages
+
+Then the main part is to define the behaviour of languages.  This
+should be easy enough, since we already have the mechanism of graphs,
+nondeterministic automata, and semirings.  All we need to do is to
+combine them together.
+
+* Testing ground
+
+I am in a strong need to test things out.  The most important one is
+to visualize each step of the derivation, in a human-friendly manner.
+I need this to examine whether my atomic languages are wrongly
+implemented, or my atomic languages are wrongly derived, or my
+understanding of the main algorithm is plain wrong.
+
+This is the main reason I started this rewrite of the package.
+