before a major refactor

I decide to adopt a new approach of recording and updating item
derivation forests.  Since this affects a lot of things, I decide to
commit before the refactor, so that I can create a branch for that
refactor.

3 files changed, 26 insertions, 55 deletions

diff --git a/grammar/src/label.rs b/grammar/src/label.rs
index 058baaf..e3f3422 100644
--- a/grammar/src/label.rs
+++ b/grammar/src/label.rs
@@ -119,6 +119,12 @@ impl GrammarLabel {
         self.end
     }
 
+    /// Set the start.
+    #[inline]
+    pub fn set_start(&mut self, pos: usize) {
+        self.start = pos;
+    }
+
     /// Return the start in the input.
     #[inline]
     pub fn start(&self) -> usize {
diff --git a/grammar/src/lib.rs b/grammar/src/lib.rs
index ab0f693..21ce2b4 100644
--- a/grammar/src/lib.rs
+++ b/grammar/src/lib.rs
@@ -25,6 +25,12 @@ use std::{
     fmt::Display,
 };
 
+/// The index of the starting non-terminal.
+///
+/// By convention this is the zero-th non-terminal.  I define this
+/// constant just for the sake of clarity.
+pub const START_NONTERMINAL: usize = 0;
+
 /// The type of a terminal.
 ///
 /// For the time being this is a wrapper around a string, but in the
@@ -478,8 +484,17 @@ impl Grammar {
 
     /// Return true if and only if the terminal can appear as the
     /// first terminal in a string expanded from the non-terminal.
+    ///
+    /// # Errors
+    ///
+    /// If `non_terminal` or `terminal` is out of bounds, the function
+    /// returns an error indicating this fact.
     #[inline]
     pub fn is_first_of(&self, non_terminal: usize, terminal: usize) -> Result<bool, Error> {
+        if terminal >= self.ter_num() {
+            return Err(Error::IndexOutOfBounds(terminal, self.ter_num()));
+        }
+
         Ok(self
             .firsts
             .get(non_terminal)
@@ -488,6 +503,11 @@ impl Grammar {
     }
 
     /// Return true if and only if the non-terminal is nullable.
+    ///
+    /// # Error
+    ///
+    /// If `non_terminal` is out of bounds, return the corresponding
+    /// error.
     #[inline]
     pub fn is_nullable(&self, non_terminal: usize) -> Result<bool, Error> {
         Ok(self
diff --git a/grammar/src/tests/test_grammar_left_closure.rs b/grammar/src/tests/test_grammar_left_closure.rs
index ffc7c0f..be1df9d 100644
--- a/grammar/src/tests/test_grammar_left_closure.rs
+++ b/grammar/src/tests/test_grammar_left_closure.rs
@@ -82,59 +82,6 @@ fn test_nfa() -> Result<(), Box<dyn std::error::Error>> {
 }
 
 #[test]
-fn test_remove_epsilon() -> Result<(), Box<dyn std::error::Error>> {
-    let mut lock = stdout().lock();
-
-    let mut grammar = new_paren_grammar()?;
-
-    writeln!(lock, "grammar:")?;
-    writeln!(lock, "{grammar}")?;
-
-    let closure = new_closure_regex(&mut grammar)?;
-
-    let mut accumulator_value: usize = 0;
-
-    for regex in closure.iter() {
-        writeln!(
-            lock,
-            "regex: {}",
-            regex.to_string_with(|tnt| {
-                match tnt {
-                    TNT::Ter(t) => {
-                        format!(
-                            "({})",
-                            grammar.name_of_tnt(grammar.unpack_tnt(t).unwrap()).unwrap()
-                        )
-                    }
-                    TNT::Non(_) => {
-                        // hyper non-terminal
-                        format!("({})", grammar.name_of_tnt(tnt).unwrap())
-                    }
-                }
-            })?
-        )?;
-        writeln!(lock, "regex len = {}", regex.nodes_len())?;
-        writeln!(lock, "offset = {accumulator_value}")?;
-
-        accumulator_value += regex.nodes_len();
-    }
-
-    writeln!(lock, "total = {accumulator_value}")?;
-
-    let mut nfa = grammar.left_closure_to_nfa(&closure)?;
-
-    #[cfg(features = "test-print-viz")]
-    nfa.print_viz("nfa_orig.gv")?;
-
-    nfa.remove_epsilon(|label| label.get_value().is_none())?;
-
-    #[cfg(features = "test-print-viz")]
-    nfa.print_viz("nfa_no_epsilon.gv")?;
-
-    Ok(())
-}
-
-#[test]
 fn test_remove_dead() -> Result<(), Box<dyn std::error::Error>> {
     let mut grammar = new_paren_grammar()?;
     let closure = new_closure_regex(&mut grammar)?;
@@ -177,8 +124,6 @@ fn test_remove_dead() -> Result<(), Box<dyn std::error::Error>> {
     #[cfg(features = "test-print-viz")]
     nfa.print_viz("nfa_orig.gv")?;
 
-    // nfa.remove_epsilon(|label| label.get_value().is_none())?;
-
     let accumulators: HashSet<usize> = accumulators.into_iter().collect();
 
     println!("accumulators = {accumulators:?}");