init i guess

crates/lopal_core/Cargo.toml

@@ -0,0 +1,12 @@
+[package]
+name = "lopal_core"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]
+rowan = "0.15.15"
+drop_bomb = "0.1.5"
+enumset = "1.1.3"
+
+[lints]
+workspace = true

crates/lopal_core/src/lib.rs

@@ -0,0 +1,8 @@
+#![feature(iter_collect_into)]
+pub mod parser;
+
+pub use parser::{
+    error::SyntaxError,
+    marker::{CompletedMarker, Marker},
+    Parser, SyntaxElement,
+};

crates/lopal_core/src/parser.rs

@@ -0,0 +1,253 @@
+use std::{cell::Cell, fmt, marker::PhantomData, mem};
+
+use enumset::{EnumSet, EnumSetType};
+use rowan::{GreenNode, GreenNodeBuilder};
+
+use crate::parser::event::NodeKind;
+
+use self::{event::Event, input::Input, marker::Marker};
+pub use {error::SyntaxError, output::ParserOutput};
+
+pub mod error;
+mod event;
+mod input;
+pub mod marker;
+pub mod output;
+
+/// 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>
+        + From<rowan::SyntaxKind>
+        + fmt::Debug
+        + Clone
+        + PartialEq
+        + Eq,
+{
+    /// EOF value. This will be used by the rest of the parser library to represent an EOF.
+    const SYNTAX_EOF: Self;
+    /// Error value. This will be used as a placeholder for associated respective errors.
+    const SYNTAX_ERROR: Self;
+    const SYNTAX_ROOT: Self;
+}
+
+pub struct Parser<'src, SyntaxKind: SyntaxElement, SyntaxErr: SyntaxError> {
+    input: Input<'src, SyntaxKind>,
+    pos: usize,
+    events: Vec<Event<SyntaxKind, SyntaxErr>>,
+    step_limit: u32,
+    steps: Cell<u32>,
+}
+
+impl<'src, 'toks, SyntaxKind: SyntaxElement, SyntaxErr: SyntaxError>
+    Parser<'src, 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
+    }
+
+    pub 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 fn finish(self) -> ParserOutput<SyntaxKind, SyntaxErr> {
+        let Self {
+            input,
+            pos,
+            mut events,
+            step_limit,
+            steps,
+        } = self;
+        let (mut raw_toks, meaningless_tokens) = input.dissolve();
+        let mut builder = GreenNodeBuilder::new();
+        // TODO: document what the hell a forward parent is
+        let mut fw_parents = Vec::new();
+        let mut errors: Vec<SyntaxErr> = Vec::new();
+        raw_toks.reverse();
+
+        // always have an implicit root node to avoid [`GreenNodeBuilder::finish()`] panicking due to multiple root elements.
+        builder.start_node(SyntaxKind::SYNTAX_ROOT.into());
+
+        for i in 0..events.len() {
+            match mem::replace(&mut events[i], Event::tombstone()) {
+                Event::Start {
+                    kind,
+                    forward_parent,
+                } => {
+                    if kind == NodeKind::Tombstone && forward_parent.is_none() {
+                        continue;
+                    }
+
+                    // resolving forward parents
+                    // temporarily jump around with the parser index and replace them with tombstones
+                    fw_parents.push(kind);
+                    let mut idx = i;
+                    let mut fp = forward_parent;
+                    while let Some(fwd) = fp {
+                        idx += fwd as usize;
+                        fp = match mem::replace(&mut events[idx], Event::tombstone()) {
+                            Event::Start {
+                                kind,
+                                forward_parent,
+                            } => {
+                                fw_parents.push(kind);
+                                forward_parent
+                            }
+                            _ => unreachable!(),
+                        }
+                    }
+
+                    // clear semantically meaningless tokens before the new tree node for aesthetic reasons
+                    while raw_toks
+                        .last()
+                        .is_some_and(|v| meaningless_tokens.contains(v.0))
+                    {
+                        // update first next Eat event
+                        match events.iter_mut().find(|ev| matches!(ev, Event::Eat { .. })) {
+                            Some(Event::Eat { count }) => *count -= 1,
+                            _ => unreachable!(),
+                        }
+
+                        // put whitespace into lst
+                        let (tok, text) = raw_toks.pop().unwrap();
+                        builder.token(tok.into(), text);
+                    }
+
+                    // insert forward parents into the tree in correct order
+                    for kind in fw_parents.drain(..).rev() {
+                        match kind {
+                            NodeKind::Syntax(kind) => builder.start_node(kind.into()),
+                            NodeKind::Error(err) => {
+                                errors.push(err);
+                                builder.start_node(SyntaxKind::SYNTAX_ERROR.into())
+                            }
+                            _ => {}
+                        }
+                    }
+                }
+                Event::Finish => builder.finish_node(),
+                Event::Eat { count } => (0..count).for_each(|_| {
+                    let (tok, text) = raw_toks.pop().unwrap();
+                    builder.token(tok.into(), text);
+                }),
+            }
+        }
+
+        // finish SYNTAX_ROOT
+        builder.finish_node();
+
+        ParserOutput {
+            green_node: builder.finish(),
+            errors,
+            _syntax_kind: PhantomData::<SyntaxKind>,
+        }
+    }
+}
+
+pub struct ParserBuilder<
+    'src,
+    SyntaxKind: SyntaxElement,
+    // SyntaxErr: SyntaxError,
+> {
+    raw_toks: Vec<(SyntaxKind, &'src str)>,
+    meaningless_token_kinds: EnumSet<SyntaxKind>,
+    step_limit: u32,
+}
+
+impl<'src, SyntaxKind: SyntaxElement> ParserBuilder<'src, SyntaxKind> {
+    pub fn new(raw_toks: Vec<(SyntaxKind, &'src str)>) -> Self {
+        Self {
+            raw_toks,
+            meaningless_token_kinds: EnumSet::new(),
+            step_limit: 4096,
+        }
+    }
+
+    /// Sets the parser step limit.
+    /// Defaults to 4096
+    pub fn step_limit(mut self, new: u32) -> Self {
+        self.step_limit = new;
+        self
+    }
+
+    pub fn add_meaningless(mut self, kind: SyntaxKind) -> Self {
+        self.meaningless_token_kinds.insert(kind);
+        self
+    }
+
+    pub fn add_meaningless_many(mut self, kind: Vec<SyntaxKind>) -> Self {
+        self.meaningless_token_kinds
+            .insert_all(kind.into_iter().collect());
+        self
+    }
+
+    pub fn build<SyntaxErr: SyntaxError>(self) -> Parser<'src, SyntaxKind, SyntaxErr> {
+        let Self {
+            raw_toks,
+            meaningless_token_kinds,
+            step_limit,
+        } = self;
+        Parser {
+            input: Input::new(raw_toks, Some(meaningless_token_kinds)),
+            pos: 0,
+            events: Vec::new(),
+            step_limit,
+            steps: Cell::new(0),
+        }
+    }
+}

crates/lopal_core/src/parser/error.rs

@@ -0,0 +1,9 @@
+use std::fmt;
+
+/// A marker trait... for now!
+// TODO: constrain that conversion to `NodeKind::Error` is enforced to be possible
+pub trait SyntaxError
+where
+    Self: fmt::Debug + Clone + PartialEq + Eq,
+{
+}

crates/lopal_core/src/parser/event.rs

@@ -0,0 +1,42 @@
+use enumset::EnumSetType;
+
+use super::{error::SyntaxError, SyntaxElement};
+
+pub enum Event<SyntaxKind: SyntaxElement, SyntaxErr: SyntaxError> {
+    Start {
+        kind: NodeKind<SyntaxKind, SyntaxErr>,
+        forward_parent: Option<usize>,
+    },
+    Finish,
+    Eat {
+        count: usize,
+    },
+}
+
+impl<SyntaxKind: SyntaxElement, SyntaxErr: SyntaxError> Event<SyntaxKind, SyntaxErr> {
+    pub fn tombstone() -> Self {
+        Self::Start {
+            kind: NodeKind::Tombstone,
+            forward_parent: None,
+        }
+    }
+}
+
+#[derive(Clone, PartialEq, Eq)]
+pub enum NodeKind<SyntaxKind: SyntaxElement, SyntaxErr: SyntaxError> {
+    Tombstone,
+    Syntax(SyntaxKind),
+    Error(SyntaxErr),
+}
+
+impl<SyntaxKind: SyntaxElement, SyntaxErr: SyntaxError> NodeKind<SyntaxKind, SyntaxErr> {
+    pub fn is_tombstone(&self) -> bool {
+        matches!(self, Self::Tombstone)
+    }
+    pub fn is_syntax(&self) -> bool {
+        matches!(self, Self::Syntax(_))
+    }
+    pub fn is_error(&self) -> bool {
+        matches!(self, Self::Error(_))
+    }
+}

crates/lopal_core/src/parser/input.rs

@@ -0,0 +1,67 @@
+use enumset::{EnumSet, EnumSetType};
+
+use super::SyntaxElement;
+
+pub struct Input<'src, SyntaxKind: SyntaxElement> {
+    raw: Vec<(SyntaxKind, &'src str)>,
+    // enumset of meaningless tokens
+    semantically_meaningless: EnumSet<SyntaxKind>,
+    // indices of non-meaningless tokens
+    meaningful_toks: Vec<usize>,
+}
+
+impl<'src, SyntaxKind: SyntaxElement> Input<'src, SyntaxKind> {
+    pub fn new(
+        raw_toks: Vec<(SyntaxKind, &'src str)>,
+        meaningless: Option<EnumSet<SyntaxKind>>,
+    ) -> Self {
+        let mut meaningful_toks = Vec::new();
+
+        if let Some(meaningless) = meaningless {
+            let meaningful_toks = raw_toks
+                .iter()
+                .enumerate()
+                .filter_map(|(i, tok)| (!meaningless.contains(tok.0)).then_some(i))
+                .collect_into(&mut meaningful_toks);
+        }
+
+        Self {
+            raw: raw_toks,
+            semantically_meaningless: meaningless.unwrap_or_default(),
+            meaningful_toks,
+        }
+    }
+
+    pub fn kind(&self, idx: usize) -> SyntaxKind {
+        let Some(meaningful_idx) = self.meaningful_toks.get(idx) else {
+            return SyntaxKind::SYNTAX_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)
+    }
+
+    pub fn dissolve(self) -> (Vec<(SyntaxKind, &'src str)>, EnumSet<SyntaxKind>) {
+        let Self {
+            raw,
+            semantically_meaningless,
+            ..
+        } = self;
+        (raw, semantically_meaningless)
+    }
+}

crates/lopal_core/src/parser/marker.rs

@@ -0,0 +1,97 @@
+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>,
+    ) {
+        self.bomb.defuse();
+
+        // clean up empty tombstone event from marker
+        if self.pos == p.events.len() - 1 {
+            match p.events.pop() {
+                Some(Event::Start {
+                    kind: NodeKind::Tombstone,
+                    forward_parent: None,
+                }) => (),
+                _ => unreachable!(),
+            }
+        }
+    }
+}
+
+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 {
+        let new_pos = p.start(name);
+
+        match &mut p.events[self.pos] {
+            Event::Start { forward_parent, .. } => {
+                // point forward parent of the node this marker completed to the new node
+                // will later be used to make the new node a parent of the current node.
+                *forward_parent = Some(new_pos.pos - self.pos)
+            }
+            _ => unreachable!(),
+        }
+
+        new_pos
+    }
+}

crates/lopal_core/src/parser/output.rs

@@ -0,0 +1,73 @@
+use std::{fmt, marker::PhantomData};
+
+use rowan::{GreenNode, GreenNodeData, GreenTokenData, NodeOrToken};
+
+use crate::{SyntaxElement, SyntaxError};
+
+pub struct ParserOutput<SyntaxKind: SyntaxElement, SyntaxErr: SyntaxError> {
+    pub green_node: GreenNode,
+    pub errors: Vec<SyntaxErr>,
+    pub(super) _syntax_kind: PhantomData<SyntaxKind>,
+}
+
+impl<SyntaxKind: SyntaxElement, SyntaxErr: SyntaxError> std::fmt::Debug
+    for ParserOutput<SyntaxKind, SyntaxErr>
+{
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        let mut errs: Vec<&SyntaxErr> = self.errors.iter().collect();
+        errs.reverse();
+        debug_print_output::<SyntaxKind, SyntaxErr>(
+            NodeOrToken::Node(&self.green_node),
+            f,
+            0,
+            &mut errs,
+        )
+    }
+}
+
+fn debug_print_output<SyntaxKind: SyntaxElement, SyntaxErr: SyntaxError>(
+    node: NodeOrToken<&GreenNodeData, &GreenTokenData>,
+    f: &mut std::fmt::Formatter<'_>,
+    lvl: i32,
+    errs: &mut Vec<&SyntaxErr>,
+) -> std::fmt::Result {
+    if f.alternate() {
+        for _ in 0..lvl {
+            f.write_str("    ")?;
+        }
+    }
+    let maybe_newline = if f.alternate() { "\n" } else { " " };
+
+    match node {
+        NodeOrToken::Node(n) => {
+            let kind: SyntaxKind = node.kind().into();
+            if kind != SyntaxKind::SYNTAX_ERROR {
+                write!(f, "{:?} {{{maybe_newline}", kind)?;
+            } else {
+                let err = errs
+                    .pop()
+                    .expect("all error syntax nodes should correspond to an error");
+
+                write!(f, "{:?}: {err:?} {{{maybe_newline}", kind)?;
+            }
+            for c in n.children() {
+                debug_print_output::<SyntaxKind, SyntaxErr>(c, f, lvl + 1, errs)?;
+            }
+
+            if f.alternate() {
+                for _ in 0..lvl {
+                    f.write_str("    ")?;
+                }
+            }
+            write!(f, "}}{maybe_newline}")
+        }
+        NodeOrToken::Token(t) => {
+            write!(
+                f,
+                "{:?} {:?};{maybe_newline}",
+                Into::<SyntaxKind>::into(t.kind()),
+                t.text()
+            )
+        }
+    }
+}

crates/lopal_json/Cargo.toml

@@ -0,0 +1,13 @@
+[package]
+name = "lopal_json"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]
+logos = "0.14.2"
+enumset = "1.1.3"
+rowan = "0.15.15"
+lopal_core = { path = "../lopal_core" }
+
+[lints]
+workspace = true

crates/lopal_json/src/grammar.rs

@@ -0,0 +1,78 @@
+use array::array;
+use enumset::{enum_set, EnumSet};
+use lopal_core::parser::ParserBuilder;
+
+use crate::{
+    syntax_error::SyntaxError,
+    syntax_kind::{lex, SyntaxKind},
+};
+
+use self::object::object;
+
+mod array;
+mod object;
+
+pub(crate) type Parser<'src> = lopal_core::Parser<'src, SyntaxKind, SyntaxError>;
+pub(crate) type CompletedMarker = lopal_core::CompletedMarker<SyntaxKind, SyntaxError>;
+
+const BASIC_VALUE_TOKENS: EnumSet<SyntaxKind> =
+    enum_set!(SyntaxKind::BOOL | SyntaxKind::NULL | SyntaxKind::NUMBER | SyntaxKind::STRING);
+
+pub fn value(p: &mut Parser) -> bool {
+    if BASIC_VALUE_TOKENS.contains(p.current()) {
+        p.do_bump();
+        return true;
+    } else {
+        object(p).or_else(|| array(p)).is_some()
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::{
+        test_utils::{check_parser, gen_checks},
+        value,
+    };
+
+    #[test]
+    fn value_lit() {
+        gen_checks! {value;
+            r#""helo world""# => r#"ROOT { STRING "\"helo world\""; }"#,
+            "42"              => r#"ROOT { NUMBER "42"; }"#,
+            "null"            => r#"ROOT { NULL "null"; }"#,
+            "true"            => r#"ROOT { BOOL "true"; }"#,
+            "false"           => r#"ROOT { BOOL "false"; }"#
+        };
+    }
+}
+
+#[cfg(test)]
+mod test_utils {
+    use lopal_core::parser::ParserBuilder;
+
+    use crate::syntax_kind::{lex, SyntaxKind};
+
+    use super::Parser;
+
+    macro_rules! gen_checks {
+        ($fn_to_test:ident; $($in:literal => $out:literal),+) => {
+            $(crate::grammar::test_utils::check_parser($in, |p| { $fn_to_test(p); }, $out);)+
+        }
+    }
+
+    pub(super) use gen_checks;
+
+    pub(super) fn check_parser(input: &str, parser_fn: fn(&mut Parser), expected_output: &str) {
+        let toks = lex(input);
+        let mut p: Parser = ParserBuilder::new(toks)
+            .add_meaningless(SyntaxKind::WHITESPACE)
+            .add_meaningless(SyntaxKind::NEWLINE)
+            .build();
+
+        parser_fn(&mut p);
+
+        let out = p.finish();
+
+        assert_eq!(format!("{out:?}").trim_end(), expected_output);
+    }
+}

crates/lopal_json/src/grammar/array.rs

@@ -0,0 +1,52 @@
+use crate::{syntax_error::SyntaxError, syntax_kind::SyntaxKind};
+
+use super::{value, CompletedMarker, Parser};
+
+pub(super) fn array(p: &mut Parser) -> Option<CompletedMarker> {
+    let array_start = p.start("array");
+
+    if !p.eat(SyntaxKind::BRACKET_OPEN) {
+        array_start.abandon(p);
+        return None;
+    }
+
+    let el = p.start("arr_el");
+    value(p);
+    el.complete(p, SyntaxKind::ELEMENT);
+
+    while p.at(SyntaxKind::COMMA) {
+        let potential_trailing_comma = p.start("potential_trailing_comma");
+
+        p.eat(SyntaxKind::COMMA);
+        let maybe_el = p.start("arr_el");
+        if !value(p) {
+            maybe_el.abandon(p);
+            potential_trailing_comma.complete(p, SyntaxKind::TRAILING_COMMA);
+        } else {
+            maybe_el.complete(p, SyntaxKind::ELEMENT);
+            potential_trailing_comma.abandon(p);
+        }
+    }
+
+    Some(if !p.eat(SyntaxKind::BRACKET_CLOSE) {
+        array_start.error(p, SyntaxError::UnclosedArray)
+    } else {
+        array_start.complete(p, SyntaxKind::ARRAY)
+    })
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::grammar::{array::array, test_utils::gen_checks};
+
+    #[test]
+    fn array_basic() {
+        gen_checks! {array;
+            r#"[1,2,3]"# => r#"ROOT { ARRAY { BRACKET_OPEN "["; ELEMENT { NUMBER "1"; } COMMA ","; ELEMENT { NUMBER "2"; } COMMA ","; ELEMENT { NUMBER "3"; } BRACKET_CLOSE "]"; } }"#,
+            r#"[1,2,]"# => r#"ROOT { ARRAY { BRACKET_OPEN "["; ELEMENT { NUMBER "1"; } COMMA ","; ELEMENT { NUMBER "2"; } TRAILING_COMMA { COMMA ","; } BRACKET_CLOSE "]"; } }"#,
+            r#"[1,2"# => r#"ROOT { PARSE_ERR: UnclosedArray { BRACKET_OPEN "["; ELEMENT { NUMBER "1"; } COMMA ","; ELEMENT { NUMBER "2"; } } }"#,
+            r#"[1,2,"# => r#"ROOT { PARSE_ERR: UnclosedArray { BRACKET_OPEN "["; ELEMENT { NUMBER "1"; } COMMA ","; ELEMENT { NUMBER "2"; } TRAILING_COMMA { COMMA ","; } } }"#,
+            r#"[{"hello":"world""# => r#"ROOT { PARSE_ERR: UnclosedArray { BRACKET_OPEN "["; ELEMENT { PARSE_ERR: UnclosedObject { BRACE_OPEN "{"; MEMBER { MEMBER_NAME { STRING "\"hello\""; } COLON ":"; MEMBER_VALUE { STRING "\"world\""; } } } } } }"#
+        }
+    }
+}

crates/lopal_json/src/grammar/object.rs

@@ -0,0 +1,92 @@
+use crate::{grammar::value, syntax_error::SyntaxError, syntax_kind::SyntaxKind};
+
+use super::{CompletedMarker, Parser, BASIC_VALUE_TOKENS};
+
+pub(super) fn object(p: &mut Parser) -> Option<CompletedMarker> {
+    let obj_start = p.start("object");
+
+    if !p.eat(SyntaxKind::BRACE_OPEN) {
+        obj_start.abandon(p);
+        return None;
+    }
+
+    member(p);
+    while p.at(SyntaxKind::COMMA) {
+        // not always an error, later configurable
+        let potential_trailing_comma = p.start("potential_trailing_comma");
+        p.eat(SyntaxKind::COMMA);
+
+        if member(p).is_none() {
+            potential_trailing_comma.complete(p, SyntaxKind::TRAILING_COMMA);
+        } else {
+            potential_trailing_comma.abandon(p);
+        }
+    }
+
+    Some(if p.eat(SyntaxKind::BRACE_CLOSE) {
+        obj_start.complete(p, SyntaxKind::OBJECT)
+    } else {
+        obj_start.error(p, SyntaxError::UnclosedObject)
+    })
+}
+
+fn member(p: &mut Parser) -> Option<CompletedMarker> {
+    let member_start = p.start("member");
+
+    if p.at(SyntaxKind::BRACE_CLOSE) {
+        member_start.abandon(p);
+        return None;
+    } else if p.at(SyntaxKind::STRING) {
+        let member_name_start = p.start("member_name");
+        p.eat(SyntaxKind::STRING);
+        member_name_start.complete(p, SyntaxKind::MEMBER_NAME);
+    } else {
+        return todo!("handle other tokens: {:?}", p.current());
+    }
+
+    if !p.eat(SyntaxKind::COLON) {
+        todo!("handle wrong tokens")
+    }
+
+    let member_value_start = p.start("member_value_start");
+    if value(p) {
+        member_value_start.complete(p, SyntaxKind::MEMBER_VALUE);
+        Some(member_start.complete(p, SyntaxKind::MEMBER))
+    } else {
+        member_value_start.abandon(p);
+        let e = member_start.error(p, SyntaxError::MemberMissingValue);
+        Some(
+            e.precede(p, "member but failed already")
+                .complete(p, SyntaxKind::MEMBER),
+        )
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::grammar::{
+        object::{member, object},
+        test_utils::gen_checks,
+    };
+
+    #[test]
+    fn object_basic() {
+        gen_checks! {object;
+            r#"{"a": "b"}"#  => r#"ROOT { OBJECT { BRACE_OPEN "{"; MEMBER { MEMBER_NAME { STRING "\"a\""; } COLON ":"; WHITESPACE " "; MEMBER_VALUE { STRING "\"b\""; } } BRACE_CLOSE "}"; } }"#,
+            r#"{"a": 42}"#   => r#"ROOT { OBJECT { BRACE_OPEN "{"; MEMBER { MEMBER_NAME { STRING "\"a\""; } COLON ":"; WHITESPACE " "; MEMBER_VALUE { NUMBER "42"; } } BRACE_CLOSE "}"; } }"#,
+            r#"{"a": "b""#   => r#"ROOT { PARSE_ERR: UnclosedObject { BRACE_OPEN "{"; MEMBER { MEMBER_NAME { STRING "\"a\""; } COLON ":"; WHITESPACE " "; MEMBER_VALUE { STRING "\"b\""; } } } }"#,
+            r#"{"a": }"#     => r#"ROOT { OBJECT { BRACE_OPEN "{"; MEMBER { PARSE_ERR: MemberMissingValue { MEMBER_NAME { STRING "\"a\""; } COLON ":"; } } WHITESPACE " "; BRACE_CLOSE "}"; } }"#,
+            r#"{"a":"#       => r#"ROOT { PARSE_ERR: UnclosedObject { BRACE_OPEN "{"; MEMBER { PARSE_ERR: MemberMissingValue { MEMBER_NAME { STRING "\"a\""; } COLON ":"; } } } }"#,
+            r#"{"a":true,}"# => r#"ROOT { OBJECT { BRACE_OPEN "{"; MEMBER { MEMBER_NAME { STRING "\"a\""; } COLON ":"; MEMBER_VALUE { BOOL "true"; } } TRAILING_COMMA { COMMA ","; } BRACE_CLOSE "}"; } }"#
+        }
+    }
+
+    #[test]
+    fn member_basic() {
+        gen_checks! {member;
+            r#""a": "b""# => r#"ROOT { MEMBER { MEMBER_NAME { STRING "\"a\""; } COLON ":"; WHITESPACE " "; MEMBER_VALUE { STRING "\"b\""; } } }"#,
+            r#""a": 42"#  => r#"ROOT { MEMBER { MEMBER_NAME { STRING "\"a\""; } COLON ":"; WHITESPACE " "; MEMBER_VALUE { NUMBER "42"; } } }"#,
+            r#""a":"#     => r#"ROOT { MEMBER { PARSE_ERR: MemberMissingValue { MEMBER_NAME { STRING "\"a\""; } COLON ":"; } } }"#
+        }
+    }
+}

crates/lopal_json/src/lib.rs

@@ -0,0 +1,3 @@
+mod grammar;
+mod syntax_error;
+mod syntax_kind;

crates/lopal_json/src/syntax_error.rs

@@ -0,0 +1,11 @@
+use crate::syntax_kind::SyntaxKind;
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub enum SyntaxError {
+    UnclosedObject,
+    UnclosedArray,
+    DisallowedKeyType(SyntaxKind),
+    MemberMissingValue,
+    UnexpectedTrailingComma,
+}
+impl lopal_core::parser::SyntaxError for SyntaxError {}

crates/lopal_json/src/syntax_kind.rs

@@ -0,0 +1,117 @@
+use logos::Logos;
+
+pub fn lex(src: &str) -> Vec<(SyntaxKind, &str)> {
+    let mut lex = SyntaxKind::lexer(src);
+    let mut r = Vec::new();
+
+    while let Some(tok_res) = lex.next() {
+        r.push((tok_res.unwrap_or(SyntaxKind::LEX_ERR), lex.slice()))
+    }
+
+    r
+}
+
+#[derive(enumset::EnumSetType, Debug, Logos, PartialEq, Eq, Clone, Copy, Hash)]
+#[repr(u16)]
+#[enumset(no_super_impls)]
+#[allow(non_camel_case_types)]
+pub enum SyntaxKind {
+    OBJECT,
+    MEMBER,
+    MEMBER_NAME,
+    MEMBER_VALUE,
+
+    ARRAY,
+    ELEMENT,
+
+    // SyntaxKinds for future json5/etc support
+    TRAILING_COMMA,
+
+    // Tokens
+    // Regexes adapted from [the logos handbook](https://logos.maciej.codes/examples/json_borrowed.html)
+    #[token("true")]
+    #[token("false")]
+    BOOL,
+    #[token("{")]
+    BRACE_OPEN,
+    #[token("}")]
+    BRACE_CLOSE,
+    #[token("[")]
+    BRACKET_OPEN,
+    #[token("]")]
+    BRACKET_CLOSE,
+    #[token(":")]
+    COLON,
+    #[token(",")]
+    COMMA,
+    #[token("null")]
+    NULL,
+    #[regex(r"-?(?:0|[1-9]\d*)(?:\.\d+)?(?:[eE][+-]?\d+)?")]
+    NUMBER,
+    #[regex(r#""([^"\\]|\\["\\bnfrt]|u[a-fA-F0-9]{4})*""#)]
+    STRING,
+
+    // Whitespace tokens
+    #[regex("[ \\t\\f]+")]
+    WHITESPACE,
+    #[token("\n")]
+    NEWLINE,
+
+    // Error SyntaxKinds
+    LEX_ERR,
+    PARSE_ERR,
+
+    // Meta SyntaxKinds
+    ROOT,
+    EOF,
+}
+
+impl lopal_core::parser::SyntaxElement for SyntaxKind {
+    const SYNTAX_EOF: Self = Self::EOF;
+
+    const SYNTAX_ERROR: Self = Self::PARSE_ERR;
+    const SYNTAX_ROOT: Self = Self::ROOT;
+}
+
+impl From<SyntaxKind> for rowan::SyntaxKind {
+    fn from(kind: SyntaxKind) -> Self {
+        Self(kind as u16)
+    }
+}
+
+impl From<rowan::SyntaxKind> for SyntaxKind {
+    fn from(raw: rowan::SyntaxKind) -> Self {
+        assert!(raw.0 <= SyntaxKind::EOF as u16);
+        #[allow(unsafe_code, reason = "The transmute is necessary here")]
+        unsafe {
+            std::mem::transmute::<u16, SyntaxKind>(raw.0)
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::syntax_kind::{lex, SyntaxKind};
+
+    #[test]
+    fn simple_object() {
+        const TEST_DATA: &str = r#"{"hello_world": "meow", "some_num":7.42}"#;
+
+        assert_eq!(
+            dbg!(lex(TEST_DATA)),
+            vec![
+                (SyntaxKind::BRACE_OPEN, "{"),
+                (SyntaxKind::STRING, "\"hello_world\""),
+                (SyntaxKind::COLON, ":"),
+                (SyntaxKind::WHITESPACE, " "),
+                (SyntaxKind::STRING, "\"meow\""),
+                (SyntaxKind::COMMA, ","),
+                (SyntaxKind::WHITESPACE, " "),
+                (SyntaxKind::STRING, "\"some_num\""),
+                (SyntaxKind::COLON, ":"),
+                (SyntaxKind::NUMBER, "7.42"),
+                (SyntaxKind::BRACE_CLOSE, "}")
+            ]
+        );
+    }
+}