NPDA's working

example.npda

@@ -2,18 +2,21 @@
 Q = {q0, q1} // states
 E = {a, b} // alphabet
 T = {z0, A, B} // stack 
-I = q0
+q0 = q0
+z0 = z0
 
 // construct all possible permutations of A's and B's
 d(q0, epsilon, z0)  =   { (q0, [A z0]), (q0, [B z0]) }
 d(q0, epsilon, A)   =   { (q0, [A A]),  (q0, [B A])  }
+
 d(q0, epsilon, B)   =   { (q0, [A B]),  (q0, [B B])  }
 
 // transition to q1
-d(q0, epsilon, z0)={ (q1, z0) }
+d(q0, epsilon, z0)  =   { (q1, z0) }
-d(q0, epsilon, A)={ (q1, A) }
+d(q0, epsilon, A)   =   { (q1, A)  }
-d(q0, epsilon, B)={ (q1, B) }
+
+//d(q0, epsilon, B)   =   { (q1, B)  }
 
 // consume stack until empty
-d(q1, a, A)={(q1, epsilon)}
+d(q1, a, A)         =   { (q1, epsilon) }
-d(q1, b, B)={(q1, epsilon)}
+d(q1, b, B)         =   { (q1, epsilon) }

src/automata/mod.rs

@@ -7,38 +7,76 @@ pub mod npda;
 pub mod ntm;
 pub mod tm;
 
+pub trait Get<Idx>{
+    type Output;
+    fn get(&self, idx: Idx) -> Option<&Self::Output>;
+    fn get_mut(&mut self, idx: Idx) -> Option<&mut Self::Output>;
+}
+
+pub trait GetDefault<Idx>{
+    type Output: Default;
+    fn get_or_insert_default(&mut self, idx: Idx) -> &Self::Output;
+    fn get_mut_or_insert_default(&mut self, idx: Idx) -> &mut Self::Output;
+}
+
+macro_rules! index {
+    ($ty: ident, $self:ident, $collection: expr, $index_calc: expr, $index: pat = $index_ty: ty $(, $default: expr)?) => {
+        impl<T> Get<$index_ty> for $ty<T> {
+            type Output = T;
+            fn get(&$self, $index: $index_ty) -> Option<&T>{
+                $collection.get($index_calc)
+            }
+
+            fn get_mut(&mut $self, $index: $index_ty) -> Option<&mut T>{
+                $collection.get_mut($index_calc)
+            }
+        }
+
+        impl<T> std::ops::Index<$index_ty> for $ty<T>{
+            type Output = T;
+
+            fn index(& $self, $index: $index_ty) -> &T{
+                $collection.get($index_calc).unwrap()
+            }
+        }
+
+        impl<T> std::ops::IndexMut<$index_ty> for $ty<T>{
+            fn index_mut(&mut $self, $index: $index_ty) -> &mut T{
+                $collection.get_mut($index_calc).unwrap()
+            }
+        }
+
+        $(
+            impl<T: Default> GetDefault<$index_ty> for $ty<T> {
+                type Output = T;
+                fn get_or_insert_default(&mut $self, $index: $index_ty) -> &T{
+                    $default
+                }
+
+                fn get_mut_or_insert_default(&mut $self, $index: $index_ty) -> &mut T{
+                    $default
+                }
+            }
+        )?
+    };
+}
+
 #[derive(Clone, Debug, Copy, Hash, PartialEq, Eq)]
 pub struct State(u16);
 
 #[derive(Clone, Debug, Copy, Hash, PartialEq, Eq)]
 pub struct Symbol(u16);
 
+
 #[derive(Clone, Debug)]
 pub struct StateMap<T>(Vec<T>);
 
-trait Get<Idx> {
+index!(StateMap, self, self.0, index.0 as usize, index = State);
-    type Output;
-    fn get(&self, index: Idx) -> Option<&Self::Output>;
-}
-
-impl<T> Get<State> for StateMap<T> {
-    type Output = T;
-
-    fn get(&self, index: State) -> Option<&Self::Output> {
-        self.0.get(index.0 as usize)
-    }
-}
 
 #[derive(Clone, Debug)]
 pub struct SymbolMap<T>(Vec<T>);
 
-impl<T> Get<Symbol> for SymbolMap<T> {
+index!(SymbolMap, self, self.0, index.0 as usize, index = Symbol);
-    type Output = T;
-
-    fn get(&self, index: Symbol) -> Option<&Self::Output> {
-        self.0.get(index.0 as usize)
-    }
-}
 
 #[derive(Clone, Debug, Default)]
 pub struct StateSymbolMap<T> {
@@ -46,40 +84,18 @@ pub struct StateSymbolMap<T> {
     max_state: u16,
 }
 
-impl<T> Get<(State, Symbol)> for StateSymbolMap<T> {
-    type Output = T;
 
-    fn get(&self, (state, symbol): (State, Symbol)) -> Option<&Self::Output> {
+index!(StateSymbolMap, self, self.map, state.0 as usize + self.max_state as usize * symbol.0 as usize, (state, symbol) = (State, Symbol));
-        self.map
+index!(StateSymbolMap, self, self.map, state.0 as usize + self.max_state as usize * symbol.0 as usize, (symbol, state) = (Symbol, State));
-            .get(state.0 as usize + self.max_state as usize * symbol.0 as usize)
+
-    }
-}
 
 #[derive(Clone, Debug, Default)]
 pub struct CharMap<T>(HashMap<char, T>);
-impl<T> Get<char> for CharMap<T> {
-    type Output = T;
 
-    fn get(&self, index: char) -> Option<&Self::Output> {
+index!(CharMap, self, self.0, &char, char = char, self.0.entry(char).or_default());
-        self.0.get(&index)
-    }
-}
 
 #[derive(Clone, Debug, Default)]
 pub struct CharEpsilonMap<T>(HashMap<Option<char>, T>);
 
-impl<T> Get<char> for CharEpsilonMap<T> {
+index!(CharEpsilonMap, self, self.0, &Some(char), char = char, self.0.entry(Some(char)).or_default());
-    type Output = T;
+index!(CharEpsilonMap, self, self.0, &char, char = Option<char>, self.0.entry(char).or_default());
-
-    fn get(&self, index: char) -> Option<&Self::Output> {
-        self.0.get(&Some(index))
-    }
-}
-
-impl<T> Get<Option<char>> for CharEpsilonMap<T> {
-    type Output = T;
-
-    fn get(&self, index: Option<char>) -> Option<&Self::Output> {
-        self.0.get(&index)
-    }
-}

src/automata/npda.rs

@@ -7,14 +7,13 @@ struct To(State, Vec<Symbol>);
 
 #[derive(Clone, Debug)]
 pub struct TransitionTable {
-    pub(in super::npda) initial_state: State,
+    initial_state: State,
     initial_stack: Symbol,
-    state_names: Vec<String>,
+    state_names: StateMap<String>,
-    symbol_names: Vec<String>,
+    symbol_names: SymbolMap<String>,
     alphabet: HashSet<char>,
 
-    accept_empty: bool,
+    final_states: Option<StateMap<bool>>,
-    final_states: Vec<bool>,
     transitions: StateSymbolMap<CharEpsilonMap<Vec<To>>>,
 }
 
@@ -31,8 +30,15 @@ pub struct Simulator {
     running: Vec<NPDA>,
 }
 
+pub enum SimulatorResult{
+    Pending,
+    Reject,
+    Accept(NPDA)
+}
+
 impl Simulator {
     pub fn begin(input: impl Into<String>, table: TransitionTable) -> Self {
+        
         Self {
             input: input.into(),
             running: vec![NPDA {
@@ -44,7 +50,8 @@ impl Simulator {
         }
     }
 
-    pub fn step(&mut self) -> Option<NPDA> {
+    pub fn step(&mut self) -> SimulatorResult {
+        println!("step, ({}) paths", self.running.len());
         let mut new = Vec::new();
         for mut npda in self.running.drain(..) {
             let Some(top) = npda.stack.pop() else {
@@ -73,10 +80,12 @@ impl Simulator {
                 .get(npda.position..)
                 .and_then(|c| c.chars().next())
             else {
-                if self.table.final_states[npda.state.0 as usize]
+                if let Some(final_states) = &self.table.final_states
-                    || self.table.accept_empty && npda.stack == [self.table.initial_stack]
+                    && final_states.get(npda.state).copied().unwrap_or_default()
                 {
-                    return Some(npda.clone());
+                    return SimulatorResult::Accept(npda.clone());
+                } else if npda.stack == [self.table.initial_stack] {
+                    return SimulatorResult::Accept(npda.clone());
                 } else {
                     continue;
                 }
@@ -100,7 +109,11 @@ impl Simulator {
             }
         }
         self.running = new;
-        None
+        if self.running.is_empty(){
+            SimulatorResult::Reject
+        }else{
+            SimulatorResult::Pending
+        }
     }
 }
 
@@ -108,7 +121,7 @@ impl Simulator {
 
 use crate::loader::{
     DELTA_LOWER, GAMMA_UPPER, SIGMA_UPPER, Spanned,
-    ast::{self, Symbol as Sym, Tuple},
+    ast::{self, Symbol as Sym},
     lexer::Lexer,
     log::Logs,
     parser::Parser,
@@ -130,11 +143,12 @@ impl TransitionTable {
         let mut initial_state = None;
         let mut initial_stack = None;
 
-        let mut states = HashSet::new();
+        let mut states = HashMap::new();
-        let mut stack_symbols = HashSet::new();
+        let mut stack_symbols = HashMap::new();
         let mut alphabet = HashSet::new();
         let mut final_states = None;
-        let mut accept_empty = false;
+
+        let mut transitions_map = HashMap::new();
 
         for Spanned(element, span) in ast {
             use Spanned as S;
@@ -152,12 +166,19 @@ impl TransitionTable {
                         let Some(ident) = item.expect_ident(&mut logs) else {
                             continue;
                         };
-                        if !states.insert(ident) {
+                        let state = match states.len().try_into() {
+                            Ok(ok) => State(ok),
+                            Err(_) => {
+                                logs.emit_error("too many states defined", item.1);
+                                State(0)
+                            }
+                        };
+                        if states.insert(ident, state).is_some() {
                             logs.emit_error("state redefined", item.1);
                         }
                     }
 
-                    if list.is_empty(){
+                    if list.is_empty() {
                         logs.emit_error("states cannot be empty", *span);
                     }
                 }
@@ -177,15 +198,18 @@ impl TransitionTable {
                             logs.emit_error("letter cannot be longer than one char", item.1);
                         }
 
-                        if !alphabet.insert(ident) {
+                        if !alphabet.insert(ident.chars().next().unwrap_or_default()) {
                             logs.emit_error("letter redefined", item.1);
                         }
                     }
-                    if list.is_empty(){
+                    if list.is_empty() {
                         logs.emit_error("alphabet cannot be empty", *span);
                     }
                 }
                 TL::Assignment(S(Dest::Ident("F"), _), list) => {
+                    if final_states.is_some() {
+                        logs.emit_error("final states already set", *span);
+                    }
                     let mut map = HashSet::new();
                     let Some(list) = list.expect_set(&mut logs) else {
                         continue;
@@ -194,16 +218,13 @@ impl TransitionTable {
                         let Some(ident) = item.expect_ident(&mut logs) else {
                             continue;
                         };
-                        if !states.contains(ident) {
+                        if let Some(state) = states.get(ident){
+                            if !map.insert(*state) {
+                                logs.emit_error("final state redefined", item.1);
+                            }
+                        } else{
                             logs.emit_error("final state not defined in set of states", item.1);
                         }
-                        if !map.insert(ident) {
-                            logs.emit_error("final states redefined", item.1);
-                        }
-                    }
-
-                    if final_states.is_some() {
-                        logs.emit_error("final states already set", *span);
                     }
                     final_states = Some(map);
                 }
@@ -218,40 +239,48 @@ impl TransitionTable {
                         let Some(ident) = item.expect_ident(&mut logs) else {
                             continue;
                         };
-                        if !stack_symbols.insert(ident) {
+                        let symbol = match stack_symbols.len().try_into() {
+                            Ok(ok) => Symbol(ok),
+                            Err(_) => {
+                                logs.emit_error("too many stack symbols defined", item.1);
+                                Symbol(0)
+                            }
+                        };
+                        if stack_symbols.insert(ident, symbol).is_some() {
                             logs.emit_error("stack symbol redefined", item.1);
                         }
                     }
 
-                    if list.is_empty(){
+                    if list.is_empty() {
                         logs.emit_error("stack symbols cannot be empty", *span);
                     }
                 }
                 TL::Assignment(S(Dest::Ident("I" | "q0"), _), S(src, src_d)) => match src {
                     ast::Item::Symbol(Sym::Ident(ident)) => {
-                        if !states.contains(ident) {
-                            logs.emit_error("initial state symbol not defined as a state", *src_d);
-                        }
                         if initial_state.is_some() {
                             logs.emit_error("initial state already set", *span);
                         }
-                        initial_state = Some(ident)
+                        if let Some(initial) = states.get(ident) {
+                            initial_state = Some(*initial)
+                        } else {
+                            logs.emit_error("initial state symbol not defined as a state", *src_d);
+                        }
                     }
                     _ => logs.emit_error("expected ident", *src_d),
                 },
                 TL::Assignment(S(Dest::Ident("S" | "z0"), _), S(src, src_d)) => match src {
                     ast::Item::Symbol(Sym::Ident(ident)) => {
-                        if !stack_symbols.contains(ident)
+                        if initial_stack.is_some() {
-                        {
+                            logs.emit_error("initial stack already set", *span);
+                        }
+                        if let Some(initial) = stack_symbols.get(ident) {
+                            initial_stack = Some(*initial)
+                        } else {
                             logs.emit_error(
                                 "initial stack symbol not defined as a stack symbol",
                                 *src_d,
                             );
                         }
-                        if initial_stack.is_some() {
-                            logs.emit_error("initial stack already set", *span);
-                        }
-                        initial_stack = Some(ident)
                     }
                     _ => logs.emit_error("expected ident", *src_d),
                 },
@@ -264,17 +293,38 @@ impl TransitionTable {
                     list,
                 ) => {
                     let list = list.set_weak();
-                    let Some((state, letter, sym)) =
+                    let Some((state, letter, stack_symbol)) =
                         tuple.as_ref().expect_npda_transition_function(&mut logs)
                     else {
                         continue;
                     };
-                    if !states.contains(state.0){
+                    let Some(state) = states.get(state.0).copied() else{
                         logs.emit_error("transition state not defined as state", state.1);
-                    }
+                        continue;
-                    if !stack_symbols.contains(sym.0){
+                    };
-                        logs.emit_error("transition stack symbol not defined as stack symbol", sym.1);
+                    let Some(stack_symbol) = stack_symbols.get(stack_symbol.0).copied() else {
-                    }
+                        logs.emit_error(
+                            "transition stack symbol not defined as stack symbol",
+                            stack_symbol.1,
+                        );
+                        continue;
+                    };
+
+                    let char = match letter.0 {
+                        Sym::Epsilon => None,
+                        Sym::Ident(val) => if let Some(char) = val.chars().next() && val.chars().count() == 1 {
+                            if !alphabet.contains(&char){
+                                logs.emit_error("transition letter not defined in alphabet", letter.1);
+                            }
+                            Some(char)
+                        }else{
+                            logs.emit_error(
+                                "transition letter can only be single character",
+                                letter.1,
+                            );
+                            None
+                        },
+                    };
 
                     for item in list {
                         let Some((next_state, stack)) = item
@@ -284,9 +334,28 @@ impl TransitionTable {
                             continue;
                         };
 
-                        if !states.contains(next_state.0){
+                        let Some(next_state) = states.get(next_state.0).copied() else {
                             logs.emit_error("transition state not defined as state", next_state.1);
-                        }
+                            continue;
+                        };
+                        
+                        let stack: Vec<_> = stack.iter().rev().filter_map(|symbol|{
+                            if matches!(symbol.0, ast::Item::Symbol(Sym::Epsilon)) {
+                                return None;
+                            }
+                            let ident = symbol.expect_ident(&mut logs)?;
+
+                            let Some(symbol) = stack_symbols.get(ident).copied() else{
+                                logs.emit_error("transition stack symbol not defined", symbol.1);
+                                return None;
+                            };
+                            Some(symbol)
+                        }).collect();
+                        
+                        transitions_map
+                            .entry((state, char, stack_symbol))
+                            .or_insert(Vec::new())
+                            .push((next_state, stack))
                     }
                 }
                 TL::Assignment(S(Dest::Function(S(name, _), _), dest_s), _) => {
@@ -303,15 +372,87 @@ impl TransitionTable {
             }
         }
 
+        if stack_symbols.is_empty() {
+            logs.emit_error_locless("stack symbols never defined");
+        }
+
+        if alphabet.is_empty() {
+            logs.emit_error_locless("alphabet never defined");
+        }
+
+        if states.is_empty() {
+            logs.emit_error_locless("states never defined");
+        }
+
+        let initial_stack = match initial_stack {
+            Some(some) => some,
+            None => {
+                if let Some(initial) = stack_symbols.get("z0") {
+                    logs.emit_warning_locless(
+                        "initial stack symbol not defined, defaulting to 'z0'",
+                    );
+                    *initial
+                } else {
+                    logs.emit_error_locless("initial stack symbol not defined");
+                    Symbol(0)
+                }
+            }
+        };
+
+        let initial_state = match initial_state {
+            Some(some) => some,
+            None => {
+                if let Some(initial) = states.get("z0") {
+                    logs.emit_warning_locless("initial state not defined, defaulting to 'q0'");
+                    *initial
+                } else {
+                    logs.emit_error_locless("initial state not defined");
+                    State(0)
+                }
+            }
+        };
+
+        let state_names = StateMap(states.iter().fold(
+            vec![String::new(); states.len()],
+            |mut a, (k, v)| {
+                a[v.0 as usize] = k.to_string();
+                a
+            },
+        ));
+        let symbol_names = SymbolMap(stack_symbols.iter().fold(
+            vec![String::new(); stack_symbols.len()],
+            |mut a, (k, v)| {
+                a[v.0 as usize] = k.to_string();
+                a
+            },
+        ));
+        let final_states = final_states.map(|f|{
+            StateMap(f.iter().fold(vec![false; states.len()], |mut a, k|{
+                a[k.0 as usize] = true;
+                a
+            }))
+        });
+
+        let mut transitions: StateSymbolMap<CharEpsilonMap<Vec<To>>> = StateSymbolMap{
+            map: vec![CharEpsilonMap::default(); stack_symbols.len() * states.len()],
+            max_state: states.len() as u16,
+        };
+        
+        for ((q, c, s), to) in transitions_map{
+            let from = &mut transitions[(q, s)];
+            for (n, ss) in to{
+                from.get_mut_or_insert_default(c).push(To(n, ss));
+            }
+        }
+
         let table = TransitionTable {
-            initial_state: crate::automata::State(0),
+            initial_state,
-            initial_stack: crate::automata::Symbol(0),
+            initial_stack,
-            state_names: Vec::new(),
+            state_names,
-            symbol_names: Vec::new(),
+            symbol_names,
-            alphabet: HashSet::new(),
+            alphabet,
-            accept_empty: false,
+            final_states,
-            final_states: Vec::new(),
+            transitions,
-            transitions: Default::default(),
         };
 
         Ok((table, logs))

src/loader/log.rs

@@ -26,10 +26,18 @@ impl<'a> Logs<'a> {
         self.logs.push(entry);
     }
 
+    pub fn emit_error_locless(&mut self, msg: impl Into<String>) {
+        self.emit(LogEntry {
+            message: msg.into(),
+            span: None,
+            level: LogLevel::Error,
+        });
+    }
+
     pub fn emit_error(&mut self, msg: impl Into<String>, span: Span) {
         self.emit(LogEntry {
             message: msg.into(),
-            span,
+            span: Some(span),
             level: LogLevel::Error,
         });
     }
@@ -37,7 +45,15 @@ impl<'a> Logs<'a> {
     pub fn emit_warning(&mut self, msg: impl Into<String>, span: Span) {
         self.emit(LogEntry {
             message: msg.into(),
-            span,
+            span: Some(span),
+            level: LogLevel::Warning,
+        });
+    }
+
+    pub fn emit_warning_locless(&mut self, msg: impl Into<String>) {
+        self.emit(LogEntry {
+            message: msg.into(),
+            span: None,
             level: LogLevel::Warning,
         });
     }
@@ -45,7 +61,7 @@ impl<'a> Logs<'a> {
     pub fn emit_info(&mut self, msg: impl Into<String>, span: Span) {
         self.emit(LogEntry {
             message: msg.into(),
-            span,
+            span: Some(span),
             level: LogLevel::Info,
         });
     }
@@ -66,7 +82,7 @@ pub enum LogLevel {
 
 pub struct LogEntry {
     pub message: String,
-    pub span: Span,
+    pub span: Option<Span>,
     pub level: LogLevel,
 }
 
@@ -93,61 +109,53 @@ impl<'a> Display for LogEntryDisplay<'a> {
         }
         writeln!(f, "{}{RESET}", self.entry.message)?;
 
-        let line_start = self
+        if let Some(span) = self.entry.span {
-            .src
+            let line_start = self.src.get(..=span.0).unwrap_or("").lines().count();
-            .get(..=self.entry.span.0)
+            let line_end = self.src.get(..span.1).unwrap_or("").lines().count();
-            .unwrap_or("")
-            .lines()
-            .count();
-        let line_end = self
-            .src
-            .get(..self.entry.span.1)
-            .unwrap_or("")
-            .lines()
-            .count();
 
-        let padding = line_end.ilog10() as usize;
+            let padding = line_end.ilog10() as usize;
 
-        let start = self
+            let start = self
-            .src
+                .src
-            .get(..self.entry.span.0)
+                .get(..span.0)
-            .and_then(|s| s.rfind('\n'))
+                .and_then(|s| s.rfind('\n'))
-            .map(|v| v + 1)
+                .map(|v| v + 1)
-            .unwrap_or(0);
+                .unwrap_or(0);
 
-        let end = self
+            let end = self
-            .src
+                .src
-            .get(self.entry.span.1..)
+                .get(span.1..)
-            .and_then(|s| s.find('\n'))
+                .and_then(|s| s.find('\n'))
-            .map(|v| v + self.entry.span.1)
+                .map(|v| v + span.1)
-            .unwrap_or(self.src.len());
+                .unwrap_or(self.src.len());
 
-        let mut index = start;
+            let mut index = start;
-        for (i, line) in self.src.get(start..end).unwrap_or("").lines().enumerate() {
+            for (i, line) in self.src.get(start..end).unwrap_or("").lines().enumerate() {
-            write!(f, "{BOLD}{CYAN}{:>padding$}: {RESET}", i + line_start)?;
+                write!(f, "{BOLD}{CYAN}{:>padding$}: {RESET}", i + line_start)?;
-            for char in line.chars() {
+                for char in line.chars() {
-                if char == '\t' {
+                    if char == '\t' {
-                    write!(f, " ")?
+                        write!(f, " ")?
-                } else {
+                    } else {
-                    write!(f, "{char}")?
+                        write!(f, "{char}")?
+                    }
                 }
-            }
+                writeln!(f)?;
-            writeln!(f)?;
+                write!(f, "{BOLD}{CYAN}")?;
-            write!(f, "{BOLD}{CYAN}")?;
+                for _ in 0..padding + 3 {
-            for _ in 0..padding + 3 {
-                write!(f, " ")?;
-            }
-            for char in line.chars() {
-                if (self.entry.span.0..self.entry.span.1).contains(&index) {
-                    write!(f, "~")?;
-                } else {
                     write!(f, " ")?;
                 }
-                index += char.len_utf8();
+                for char in line.chars() {
+                    if (span.0..span.1).contains(&index) {
+                        write!(f, "~")?;
+                    } else {
+                        write!(f, " ")?;
+                    }
+                    index += char.len_utf8();
+                }
+                write!(f, "{RESET}")?;
+                index += '\n'.len_utf8();
+                writeln!(f)?;
             }
-            write!(f, "{RESET}")?;
-            index += '\n'.len_utf8();
-            writeln!(f)?;
         }
 
         Ok(())

src/loader/parser.rs

@@ -6,7 +6,8 @@ use super::lexer::{Lexer, Token};
 use std::iter::Peekable;
 
 pub struct Parser<'a> {
-    lexer: Peekable<Lexer<'a>>,
+    lexer: Lexer<'a>,
+    peek: Option<Spanned<Token<'a>>>,
     logs: Logs<'a>,
     src: &'a str,
     eof: Span,
@@ -18,11 +19,15 @@ impl<'a> Parser<'a> {
             eof: lexer.eof_span(),
             src: lexer.input(),
             logs: Logs::new(lexer.input()),
-            lexer: lexer.peekable(),
+            peek: None,
+            lexer,
         }
     }
 
     fn next_token(&mut self) -> Option<Spanned<Token<'a>>> {
+        if self.peek.is_some(){
+            return self.peek.take()
+        }
         loop {
             match self.lexer.next()? {
                 Spanned(Ok(Token::Comment(_)), _) => {}
@@ -33,12 +38,10 @@ impl<'a> Parser<'a> {
     }
 
     fn peek_token(&mut self) -> Option<Spanned<Token<'a>>> {
-        loop {
+        if self.peek.is_none(){
-            match *self.lexer.peek()? {
+            self.peek = self.next_token();
-                Spanned(Ok(ok), r) => return Some(Spanned(ok, r)),
-                Spanned(Err(err), span) => self.logs.emit_error(format!("lexer: {err:?}"), span),
-            }
         }
+        self.peek
     }
 
     fn expect_token(&mut self, expected: Token<'a>) -> (bool, Span) {
@@ -125,6 +128,7 @@ impl<'a> Parser<'a> {
             Some(Spanned(Token::LPar, _)) => self.parse_tupple().map(Item::Tuple),
             Some(Spanned(Token::LBrace | Token::LBracket, _)) => self.parse_list().map(Item::List),
             Some(Spanned(got, span)) => {
+                self.next_token();
                 self.logs.emit_error(
                     format!(
                         "unexpected token {:#}, expected {:}|{:}|{:}|{:}|{:}",

src/main.rs

@@ -17,4 +17,21 @@ fn main() {
             return;
         }
     };
+
+    let input = "aababaab";
+    println!("running on: '{input}'");
+    let mut simulator = npda::Simulator::begin(input, table);
+    loop {
+        match simulator.step(){
+            npda::SimulatorResult::Pending => {},
+            npda::SimulatorResult::Reject => {
+                println!("REJECTED");
+                break;
+            },
+            npda::SimulatorResult::Accept(npda) => {
+                println!("ACCEPT: {npda:?}");
+                break;
+            },
+        }
+    }
 }