No Vocabulary is insufficient for Index

src/error.rs

@@ -5,8 +5,6 @@ pub type Result<T, E = crate::Error> = std::result::Result<T, E>;
 #[derive(Error, Debug)]
 pub enum Error {
     // Index Errors
-    #[error("The vocabulary does not allow to build an index that matches the input")]
-    InsufficientVocabulary,
     #[error("Failed to build DFA {0}")]
     IndexDfaError(#[from] Box<regex_automata::dfa::dense::BuildError>),
     #[error("Index failed since anchored universal start state doesn't exist")]

src/index.rs

@@ -14,15 +14,44 @@ pub struct Index {
     initial_state: StateId,
     /// A collection of states considered as terminal states.
     final_states: HashSet<StateId>,
-    /// A mapping of state transitions, defined by tokens ids and their corresponding state changes:
-    ///   - The outer map's keys are the state IDs.
-    ///   - The inner map's keys are token IDs.
-    ///   - The inner map's values are state IDs, indicating transitions to the next state.
+    /// A mapping of state transitions, defined by tokens ids and their corresponding state changes.
+    ///
+    /// ### Example
+    /// ```
+    /// transitions = {
+    ///    1: {10: 2, 15: 3},
+    ///    2: {20: 4, 25: 3},
+    ///    3: {30: 4},
+    ///    4: {40: 4},
+    /// }
+    ///  +--------------------------------------+
+    ///  |               State 1                |
+    ///  |            Initial State             |
+    ///  +--------------------------------------+
+    ///              |                     |
+    ///              +                     |
+    ///         Token ID 10                |
+    ///  +-----------------------+         |
+    ///  |        State 2        |         |
+    ///  +-----------------------+         |
+    ///       |             |              |
+    ///       |             +              +
+    ///       |        Token ID 25    Token ID 15
+    ///       |        +------------------------+
+    ///       |        |        State 3         |
+    ///       |        +------------------------+
+    ///       |                            |
+    ///       +                            +
+    ///  Token ID 20                  Token ID 30
+    ///  +--------------------------------------+
+    ///  |               State 4                |
+    ///  |             Final state              |
+    ///  +--------------------------------------+
+    /// ```
     transitions: HashMap<StateId, HashMap<TokenId, StateId>>,
     /// The token ID reserved for the "end-of-sequence" token.
     eos_token_id: TokenId,
 }
-
 /// The `Index` structure is designed to efficiently map tokens from a given vocabulary
 /// to state transitions within a finite-state automaton.
 ///
@@ -122,30 +151,19 @@ impl Index {
                 .insert(eos_token_id, final_state);
         }
 
-        // Check if there is at least one valid mapping
-        let is_valid = transitions.values().any(|mapping| {
-            mapping
-                .values()
-                .any(|end_state| final_states.contains(end_state))
-        });
-
-        if is_valid {
-            Ok(Self {
-                initial_state: start_state.as_u32(),
-                final_states,
-                transitions,
-                eos_token_id,
-            })
-        } else {
-            Err(Error::InsufficientVocabulary)
-        }
+        Ok(Self {
+            initial_state: start_state.as_u32(),
+            final_states,
+            transitions,
+            eos_token_id,
+        })
     }
 
     /// Lists allowed tokens for a give state ID or `None` if it is not found in `Index`.
     pub fn allowed_tokens(&self, state: &StateId) -> Option<Vec<TokenId>> {
         self.transitions
             .get(state)
-            .map_or_else(|| None, |res| Some(res.keys().cloned().collect()))
+            .map(|res| res.keys().cloned().collect())
     }
 
     /// Returns transition state for a given state and token id or `None` otherwise.
@@ -259,7 +277,6 @@ mod tests {
         }
 
         let index = Index::new(regex, &vocabulary).expect("Index failed");
-
         assert_eq!(index.final_states(), &HashSet::from_iter([208, 128]));
 
         let expected = HashMap::from_iter([