pawarser(setup): continue working on the bare basics

crates/pawarser/src/parser.rs

@@ -2,18 +2,25 @@ use std::cell::Cell;
 
 use enumset::{EnumSet, EnumSetType};
 
-use self::{error::SyntaxError, event::Event, input::Input};
+use self::{error::SyntaxError, event::Event, input::Input, marker::Marker};
 
 mod error;
 mod event;
-pub mod input;
+mod input;
+mod marker;
 
-pub struct Parser<
-    'src,
-    'toks,
-    SyntaxKind: EnumSetType + Into<rowan::SyntaxKind>,
-    SyntaxErr: SyntaxError,
-> {
+/// this is used to define some required SyntaxKinds like an EOF token or an error token
+pub trait SyntaxElement
+where
+    Self: EnumSetType + Into<rowan::SyntaxKind> + Clone,
+{
+    /// EOF value. This will be used by the rest of the parser library to represent an EOF.
+    const EOF: Self;
+    /// Error value. This will be used as a placeholder for associated respective errors.
+    const ERROR: Self;
+}
+
+pub struct Parser<'src, 'toks, SyntaxKind: SyntaxElement, SyntaxErr: SyntaxError> {
     input: Input<'src, 'toks, SyntaxKind>,
     pos: usize,
     events: Vec<Event<SyntaxKind, SyntaxErr>>,
@@ -21,10 +28,76 @@ pub struct Parser<
     steps: Cell<u32>,
 }
 
+impl<'src, 'toks, SyntaxKind: SyntaxElement, SyntaxErr: SyntaxError>
+    Parser<'src, 'toks, SyntaxKind, SyntaxErr>
+{
+    /// eat all meaningless tokens at the end of the file.
+    pub fn eat_succeeding_meaningless(&mut self) {
+        self.push_ev(Event::Eat {
+            count: self.input.meaningless_tail_len(),
+        });
+    }
+
+    /// Get token from current position of the parser.
+    pub fn current(&self) -> SyntaxKind {
+        self.step();
+        self.input.kind(self.pos)
+    }
+
+    pub fn start(&mut self, name: &str) -> Marker {
+        let pos = self.events.len();
+        self.push_ev(Event::tombstone());
+        Marker::new(pos, name)
+    }
+
+    /// Eat next token if it's of kind `kind` and return `true`.
+    /// Otherwise, `false`.
+    pub fn eat(&mut self, kind: SyntaxKind) -> bool {
+        if !self.at(kind) {
+            return false;
+        }
+
+        self.do_bump();
+        true
+    }
+
+    fn do_bump(&mut self) {
+        self.push_ev(Event::Eat {
+            count: self.input.preceding_meaningless(self.pos),
+        });
+        self.pos += 1;
+    }
+
+    /// Check if the token at the current parser position is of `kind`
+    pub fn at(&self, kind: SyntaxKind) -> bool {
+        self.nth_at(0, kind)
+    }
+
+    /// Check if the token that is `n` ahead is of `kind`
+    pub fn nth_at(&self, n: usize, kind: SyntaxKind) -> bool {
+        self.nth(n) == kind
+    }
+
+    pub fn nth(&self, n: usize) -> SyntaxKind {
+        self.step();
+        self.input.kind(self.pos + n)
+    }
+
+    fn push_ev(&mut self, event: Event<SyntaxKind, SyntaxErr>) {
+        self.events.push(event);
+    }
+
+    fn step(&self) {
+        let steps = self.steps.get();
+        assert!(steps <= self.step_limit, "the parser seems stuck.");
+        self.steps.set(steps + 1);
+    }
+}
+
 pub struct ParserBuilder<
     'src,
     'toks,
-    SyntaxKind: EnumSetType + Into<rowan::SyntaxKind>,
+    SyntaxKind: SyntaxElement,
     // SyntaxErr: SyntaxError,
 > {
     raw_toks: &'toks Vec<(SyntaxKind, &'src str)>,
@@ -32,9 +105,7 @@ pub struct ParserBuilder<
     step_limit: u32,
 }
 
-impl<'src, 'toks, SyntaxKind: EnumSetType + Into<rowan::SyntaxKind>>
-    ParserBuilder<'src, 'toks, SyntaxKind>
-{
+impl<'src, 'toks, SyntaxKind: SyntaxElement> ParserBuilder<'src, 'toks, SyntaxKind> {
     pub fn new(raw_toks: &'toks Vec<(SyntaxKind, &'src str)>) -> Self {
         Self {
             raw_toks,

crates/pawarser/src/parser/error.rs

@@ -1,3 +1,7 @@
 /// A marker trait... for now!
 // TODO: constrain that conversion to `NodeKind::Error` is enforced to be possible
-pub trait SyntaxError {}
+pub trait SyntaxError
+where
+    Self: Clone,
+{
+}

crates/pawarser/src/parser/event.rs

@@ -1,8 +1,8 @@
 use enumset::EnumSetType;
 
-use super::error::SyntaxError;
+use super::{error::SyntaxError, SyntaxElement};
 
-pub enum Event<SyntaxKind: EnumSetType + Into<rowan::SyntaxKind>, SyntaxErr: SyntaxError> {
+pub enum Event<SyntaxKind: SyntaxElement, SyntaxErr: SyntaxError> {
     Start {
         kind: NodeKind<SyntaxKind, SyntaxErr>,
         forward_parent: Option<usize>,
@@ -13,9 +13,7 @@ pub enum Event<SyntaxKind: EnumSetType + Into<rowan::SyntaxKind>, SyntaxErr: Syn
     },
 }
 
-impl<SyntaxKind: EnumSetType + Into<rowan::SyntaxKind>, SyntaxErr: SyntaxError>
-    Event<SyntaxKind, SyntaxErr>
-{
+impl<SyntaxKind: SyntaxElement, SyntaxErr: SyntaxError> Event<SyntaxKind, SyntaxErr> {
     pub fn tombstone() -> Self {
         Self::Start {
             kind: NodeKind::Tombstone,
@@ -24,15 +22,14 @@ impl<SyntaxKind: EnumSetType + Into<rowan::SyntaxKind>, SyntaxErr: SyntaxError>
     }
 }
 
-pub enum NodeKind<SyntaxKind: EnumSetType + Into<rowan::SyntaxKind>, SyntaxErr: SyntaxError> {
+#[derive(Clone)]
+pub enum NodeKind<SyntaxKind: SyntaxElement, SyntaxErr: SyntaxError> {
     Tombstone,
     Syntax(SyntaxKind),
     Error(SyntaxErr),
 }
 
-impl<SyntaxKind: EnumSetType + Into<rowan::SyntaxKind>, SyntaxErr: SyntaxError>
-    NodeKind<SyntaxKind, SyntaxErr>
-{
+impl<SyntaxKind: SyntaxElement, SyntaxErr: SyntaxError> NodeKind<SyntaxKind, SyntaxErr> {
     pub fn is_tombstone(&self) -> bool {
         matches!(self, Self::Tombstone)
     }

crates/pawarser/src/parser/input.rs

@@ -1,6 +1,8 @@
 use enumset::{EnumSet, EnumSetType};
 
-pub struct Input<'src, 'toks, SyntaxKind: EnumSetType + Into<rowan::SyntaxKind>> {
+use super::SyntaxElement;
+
+pub struct Input<'src, 'toks, SyntaxKind: SyntaxElement> {
     raw: &'toks Vec<(SyntaxKind, &'src str)>,
     // enumset of meaningless tokens
     semantically_meaningless: EnumSet<SyntaxKind>,
@@ -8,9 +10,7 @@ pub struct Input<'src, 'toks, SyntaxKind: EnumSetType + Into<rowan::SyntaxKind>>
     meaningful_toks: Vec<usize>,
 }
 
-impl<'src, 'toks, SyntaxKind: EnumSetType + Into<rowan::SyntaxKind>>
-    Input<'src, 'toks, SyntaxKind>
-{
+impl<'src, 'toks, SyntaxKind: SyntaxElement> Input<'src, 'toks, SyntaxKind> {
     pub fn new(
         raw_toks: &'toks Vec<(SyntaxKind, &'src str)>,
         meaningless: Option<EnumSet<SyntaxKind>>,
@@ -31,4 +31,28 @@ impl<'src, 'toks, SyntaxKind: EnumSetType + Into<rowan::SyntaxKind>>
             meaningful_toks,
         }
     }
+
+    pub fn kind(&self, idx: usize) -> SyntaxKind {
+        let Some(meaningful_idx) = self.meaningful_toks.get(idx) else {
+            return SyntaxKind::EOF;
+        };
+
+        self.raw.get(*meaningful_idx).unwrap().0
+    }
+
+    pub fn preceding_meaningless(&self, idx: usize) -> usize {
+        assert!(self.meaningful_toks.len() > idx);
+
+        if idx == 0 {
+            // maybe should be `self.meaningful_toks[idx]` instead??
+            1
+        } else {
+            self.meaningful_toks[idx] - self.meaningful_toks[idx - 1]
+        }
+    }
+
+    /// get the count of meaningless tokens at the end of the file.
+    pub fn meaningless_tail_len(&self) -> usize {
+        self.raw.len() - (self.meaningful_toks.last().unwrap() + 1)
+    }
 }

crates/pawarser/src/parser/marker.rs

@@ -0,0 +1,74 @@
+use drop_bomb::DropBomb;
+use rowan::SyntaxKind;
+
+use super::{
+    error::SyntaxError,
+    event::{Event, NodeKind},
+    Parser, SyntaxElement,
+};
+
+pub struct Marker {
+    pos: usize,
+    bomb: DropBomb,
+}
+
+impl Marker {
+    pub(super) fn new(pos: usize, name: &str) -> Self {
+        Self {
+            pos,
+            bomb: DropBomb::new(format!("Marker {name} must be completed or abandoned.")),
+        }
+    }
+
+    fn close_node<SyntaxKind: SyntaxElement, SyntaxErr: SyntaxError>(
+        mut self,
+        p: &mut Parser<SyntaxKind, SyntaxErr>,
+        kind: NodeKind<SyntaxKind, SyntaxErr>,
+    ) -> CompletedMarker<SyntaxKind, SyntaxErr> {
+        self.bomb.defuse();
+
+        match &mut p.events[self.pos] {
+            Event::Start { kind: slot, .. } => *slot = kind.clone(),
+            _ => unreachable!(),
+        }
+
+        p.push_ev(Event::Finish);
+        CompletedMarker {
+            pos: self.pos,
+            kind,
+        }
+    }
+
+    pub fn complete<SyntaxKind: SyntaxElement, SyntaxErr: SyntaxError>(
+        self,
+        p: &mut Parser<SyntaxKind, SyntaxErr>,
+        kind: SyntaxKind,
+    ) -> CompletedMarker<SyntaxKind, SyntaxErr> {
+        self.close_node(p, NodeKind::Syntax(kind))
+    }
+
+    pub fn error<SyntaxKind: SyntaxElement, SyntaxErr: SyntaxError>(
+        self,
+        p: &mut Parser<SyntaxKind, SyntaxErr>,
+        kind: SyntaxErr,
+    ) -> CompletedMarker<SyntaxKind, SyntaxErr> {
+        self.close_node(p, NodeKind::Error(kind))
+    }
+
+    pub fn abandon<SyntaxKind: SyntaxElement, SyntaxErr: SyntaxError>(
+        mut self,
+        p: &mut Parser<SyntaxKind, SyntaxErr>,
+    ) {
+    }
+}
+
+pub struct CompletedMarker<SyntaxKind: SyntaxElement, SyntaxErr: SyntaxError> {
+    pos: usize,
+    kind: NodeKind<SyntaxKind, SyntaxErr>,
+}
+
+impl<SyntaxKind: SyntaxElement, SyntaxErr: SyntaxError> CompletedMarker<SyntaxKind, SyntaxErr> {
+    pub fn precede(self, p: &mut Parser<SyntaxKind, SyntaxErr>, name: &str) -> Marker {
+        todo!()
+    }
+}