diff --git a/Cargo.lock b/Cargo.lock
index e9a3e91..037ec6d 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -25,12 +25,31 @@ version = "3.13.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "a3e2c3daef883ecc1b5d58c15adae93470a91d425f3532ba1695849656af3fc1"
 
+[[package]]
+name = "cc"
+version = "1.0.83"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f1174fb0b6ec23863f8b971027804a42614e347eafb0a95bf0b12cdae21fc4d0"
+dependencies = [
+ "libc",
+]
+
 [[package]]
 name = "cfg-if"
 version = "1.0.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "baf1de4339761588bc0619e3cbc0120ee582ebb74b53b4efbf79117bd2da40fd"
 
+[[package]]
+name = "chumsky"
+version = "1.0.0-alpha.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "cc3172a80699de358070dd99f80ea8badc6cdf8ac2417cb5a96e6d81bf5fe06d"
+dependencies = [
+ "hashbrown",
+ "stacker",
+]
+
 [[package]]
 name = "fnv"
 version = "1.0.7"
@@ -55,6 +74,12 @@ dependencies = [
  "hashbrown",
 ]
 
+[[package]]
+name = "libc"
+version = "0.2.148"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9cdc71e17332e86d2e1d38c1f99edcb6288ee11b815fb1a4b049eaa2114d369b"
+
 [[package]]
 name = "literify"
 version = "0.2.0"
@@ -128,6 +153,15 @@ dependencies = [
  "unicode-ident",
 ]
 
+[[package]]
+name = "psm"
+version = "0.1.21"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5787f7cda34e3033a72192c018bc5883100330f362ef279a8cbccfce8bb4e874"
+dependencies = [
+ "cc",
+]
+
 [[package]]
 name = "quote"
 version = "1.0.33"
@@ -148,12 +182,26 @@ name = "rhea"
 version = "0.1.0"
 dependencies = [
  "bumpalo",
+ "chumsky",
  "lasso",
  "literify",
  "logos",
  "paste",
 ]
 
+[[package]]
+name = "stacker"
+version = "0.1.15"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "c886bd4480155fd3ef527d45e9ac8dd7118a898a46530b7b94c3e21866259fce"
+dependencies = [
+ "cc",
+ "cfg-if",
+ "libc",
+ "psm",
+ "winapi",
+]
+
 [[package]]
 name = "syn"
 version = "2.0.33"
@@ -176,3 +224,25 @@ name = "version_check"
 version = "0.9.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "49874b5167b65d7193b8aba1567f5c7d93d001cafc34600cee003eda787e483f"
+
+[[package]]
+name = "winapi"
+version = "0.3.9"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5c839a674fcd7a98952e593242ea400abe93992746761e38641405d28b00f419"
+dependencies = [
+ "winapi-i686-pc-windows-gnu",
+ "winapi-x86_64-pc-windows-gnu",
+]
+
+[[package]]
+name = "winapi-i686-pc-windows-gnu"
+version = "0.4.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ac3b87c63620426dd9b991e5ce0329eff545bccbbb34f3be09ff6fb6ab51b7b6"
+
+[[package]]
+name = "winapi-x86_64-pc-windows-gnu"
+version = "0.4.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "712e227841d057c1ee1cd2fb22fa7e5a5461ae8e48fa2ca79ec42cfc1931183f"
diff --git a/Cargo.toml b/Cargo.toml
index 5ed8fcb..79bd5e0 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -5,6 +5,7 @@ edition = "2021"
 
 [dependencies]
 bumpalo  = { version = "3", features = ["collections"] }
+chumsky  = "1.0.0-alpha"
 lasso    = "0.7"
 literify = "0.2"
 logos    = "0.13"
diff --git a/src/main.rs b/src/main.rs
index 3caf743..209aebe 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,5 +1,7 @@
 // Rhea
 
+use {logos::Logos, syntax::token::Token};
+
 mod syntax;
 mod utils;
 
@@ -14,12 +16,7 @@ fn main() -> Result<(), Box<dyn std::error::Error>> {
     stdin().read_to_string(&mut buf)?;
 
     let arena = Bump::new();
-    match syntax::parser::parse(&buf, &arena) {
-        Ok(ast) => println!("{ast:?}"),
-        Err(e) => {
-            eprintln!("[ERROR] {e:?}");
-            eprintln!("        Caused at: `{}`", &buf[e.span.start..e.span.end])
-        }
-    }
+    syntax::parser::parse_lexer(Token::lexer(&buf), &arena);
+    
     Ok(())
 }
diff --git a/src/syntax/ast.rs b/src/syntax/ast.rs
index b687cfd..8594459 100644
--- a/src/syntax/ast.rs
+++ b/src/syntax/ast.rs
@@ -1,32 +1,21 @@
-use lasso::Spur;
-
-#[derive(Clone, Copy, Debug, PartialEq, Eq)]
-pub struct Span {
-    pub start: usize,
-    pub end:   usize,
-}
-
-impl From<std::ops::Range<usize>> for Span {
-    fn from(value: std::ops::Range<usize>) -> Self {
-        Self {
-            start: value.start,
-            end:   value.end,
-        }
-    }
-}
+use {chumsky::span::SimpleSpan, lasso::Spur};
 
 #[derive(Clone, Copy, Debug, PartialEq, Eq)]
 pub struct Spanned<T> {
     pub item: T,
-    pub span: Span,
+    pub span: SimpleSpan,
 }
 
 impl<T> Spanned<T> {
     #[inline]
-    pub fn new(item: T, span: impl Into<Span>) -> Self {
-        Self {
-            item,
-            span: span.into(),
+    pub const fn new(item: T, span: SimpleSpan) -> Self {
+        Self { item, span }
+    }
+
+    pub fn map<U>(self, mut f: impl FnMut(T) -> U) -> Spanned<U> {
+        Spanned {
+            item: f(self.item),
+            span: self.span,
         }
     }
 }
@@ -72,7 +61,7 @@ pub enum Definition<'a> {
         init:  ExprRef<'a>,
     },
     Func {
-        name:  Spanned<Ident>,
+        name:   Spanned<Ident>,
         params: &'a [(Spanned<Ident>, Spanned<Type>)],
         ret:    Spanned<Type>,
         body:   ExprList<'a>,
diff --git a/src/syntax/parser.rs b/src/syntax/parser.rs
index 644e5cb..1fc6a1a 100644
--- a/src/syntax/parser.rs
+++ b/src/syntax/parser.rs
@@ -1,204 +1,155 @@
+use super::ast::{DefKind, Expr, ExprList, Type};
+
 use {
     super::{
-        ast::{DefKind, Definition, Expr, ExprList, Ident, Spanned, Type},
-        token::Token,
+        ast::{Definition, Ident, SpanExpr, Spanned},
+        token::{Token, T},
     },
-    crate::syntax::token::T,
-    bumpalo::{vec, Bump},
-    logos::Logos,
+    crate::utils::Pipe,
+    bumpalo::Bump,
+    chumsky::{
+        extra::Full,
+        input::{Stream, ValueInput},
+        prelude::*,
+    },
+    logos::Lexer,
 };
 
-type Lexer<'a> = logos::Lexer<'a, Token>;
-
-macro_rules! extract {
-    ($self:expr, $pat:pat) => {
-        let $pat = $self.next()? else {
-            return Err($self.error(ErrorKind::UnexpectedToken));
-        };
+/// Equivalently-named unit variant mapping
+macro_rules! equivmap {
+    ($src:ident, $target:ident, [$variant0:ident $(, $variant:ident)* $(,)?] $(,)?) => {
+        just($src::$variant0).to($target::$variant0)
+            $(.or(just($src::$variant).to($target::$variant)))*
     };
 }
 
-macro_rules! let_until {
-    (
-        $self:expr,
-        let $bind:pat,
-        until |$next:pat_param| $cond:expr,
-        $expr:expr
-        $(,)?
-    ) => {
-        loop {
-            let $next = $self.next()?;
-            if $cond {
-                break;
-            }
-
-            let $bind = $self.next()? else {
-                return Err($self.error(ErrorKind::UnexpectedToken));
-            };
-
-            $expr;
-        }
-    };
+fn ident<'a, I>() -> impl Parser<'a, I, Spanned<Ident>, Extra<'a>> + Clone + Copy
+where
+    I: Input<'a, Token = Token, Span = SimpleSpan> + ValueInput<'a>,
+{
+    select!(Token::Ident(id) => id).map_with_span(Spanned::new)
 }
 
-struct Parser<'a, 'l> {
+fn ty<'a, I>() -> impl Parser<'a, I, Spanned<Type>, Extra<'a>> + Clone + Copy
+where
+    I: Input<'a, Token = Token, Span = SimpleSpan> + ValueInput<'a>,
+{
+    ident().map(|i| i.map(Type::Ident))
+}
+
+fn definition<'a, I>() -> impl Parser<'a, I, Spanned<Definition<'a>>, Extra<'a>> + Clone
+where
+    I: Input<'a, Token = Token, Span = SimpleSpan> + ValueInput<'a>,
+{
+    let ident = ident();
+    let ty = ty();
+
+    let func = just(T!["func"])
+        .ignore_then(ident)
+        .then(
+            ident
+                .then_ignore(just(T![":"]))
+                .then(ty)
+                .separated_by(just(T![","]))
+                .allow_trailing()
+                .pipe(arena_collect)
+                .delimited_by(just(T!["("]), just(T![")"])),
+        )
+        .then_ignore(just(T!["→"]))
+        .then(ty)
+        .then(just([T!["{"], T!["}"]]))
+        .map_with_state(
+            |(((name, params), ret), _body), _, state| Definition::Func {
+                name,
+                params,
+                ret,
+                body: state.arena.alloc_slice_copy(&[]),
+            },
+        );
+
+    let binding = equivmap!(Token, DefKind, [Const, Var])
+        .then(ident)
+        .then(just(T![":"]).ignore_then(ty).or_not())
+        .then(
+            just(T!["="]).ignore_then(
+                just(T!["uninit"])
+                    .to(Expr::Uninit)
+                    .map_with_span(Spanned::new),
+            ),
+        )
+        .map_with_state(
+            |(((kind, ident), ty), init), _, state| Definition::Binding {
+                kind,
+                ident,
+                ty,
+                init: state.arena.alloc(init),
+            },
+        );
+
+    func.or(binding).map_with_span(Spanned::new)
+}
+
+pub struct State<'a> {
+    pub arena: &'a Bump,
+}
+
+type Extra<'a> = Full<Rich<'a, Token>, State<'a>, ()>;
+type ParseResult = ();
+
+pub fn parse_input<'a>(
+    input: impl ValueInput<'a, Token = Token, Span = SimpleSpan>,
     arena: &'a Bump,
-    lexer: Lexer<'l>,
+) -> ParseResult {
+    println!(
+        "{:?}",
+        definition().parse_with_state(input, &mut State { arena })
+    );
 }
 
-impl<'a, 'l> Parser<'a, 'l> {
-    /// Poll next token
-    fn next(&mut self) -> Result<Token> {
-        match self.lexer.next() {
-            Some(Ok(token)) => Ok(token),
-            Some(Err(())) => Err(ErrorKind::InvalidToken),
-            None => Err(ErrorKind::UnexpectedEnd),
-        }
-        .map_err(|k| Spanned::new(k, self.lexer.span()))
-    }
-
-    /// Form an error
-    #[inline]
-    fn error(&self, kind: ErrorKind) -> Error {
-        Spanned::new(kind, self.lexer.span())
-    }
-
-    /// Mark with current span
-    #[inline]
-    fn spanned<T>(&self, item: T) -> Spanned<T> {
-        Spanned::new(item, self.lexer.span())
-    }
-
-    /// Require a token to be
-    fn require(&mut self, token: Token) -> Result<()> {
-        if self.next()? != token {
-            Err(self.error(ErrorKind::UnexpectedToken))
-        } else {
-            Ok(())
-        }
-    }
-
-    /// Parse everything or DIE!
-    fn run(mut self) -> Result<&'a [Definition<'a>]> {
-        let mut defs = vec![in self.arena];
-        loop {
-            match self.lexer.next() {
-                Some(Ok(Token::Func)) => {
-                    defs.push(self.func()?);
-                }
-                Some(Ok(Token::Const)) => defs.push(self.var_def(DefKind::Const)?),
-                Some(Ok(Token::Var)) => defs.push(self.var_def(DefKind::Var)?),
-                Some(Ok(_)) => return Err(self.error(ErrorKind::UnexpectedToken)),
-                Some(Err(())) => return Err(self.error(ErrorKind::InvalidToken)),
-                None => return Ok(defs.into_bump_slice()),
-            }
-        }
-    }
-
-    fn ident(&mut self) -> Result<Spanned<Ident>> {
-        extract!(self, Token::Ident(id));
-        Ok(self.spanned(id))
-    }
-
-    fn ty(&mut self) -> Result<Spanned<Type>> {
-        extract!(self, Token::Ident(id));
-        Ok(self.spanned(Type::Ident(id)))
-    }
-
-    fn block(&mut self) -> Result<ExprList<'a>> {
-        self.require(T!["{"])?;
-        // TODO
-        self.require(T!["}"])?;
-
-        Ok(self.arena.alloc_slice_copy(&[]))
-    }
-
-    fn var_def(&mut self, kind: DefKind) -> Result<Definition<'a>> {
-        // <kind> <ident> [: <ty>] = <expr>;
-        // ^^^^^^
-
-        extract!(self, Token::Ident(id));
-        let ident = self.spanned(id);
-
-        let ty = match self.next()? {
-            Token::Colon => {
-                let r = Some(self.ty()?);
-                self.require(T!["="])?;
-                r
-            }
-            Token::Equ => None,
-            _ => return Err(self.error(ErrorKind::UnexpectedToken)),
-        };
-
-        self.require(T!["uninit"])?;
-        self.require(T![";"])?;
-
-        Ok(Definition::Binding {
-            kind,
-            ident,
-            ty,
-            init: self.arena.alloc(self.spanned(Expr::Uninit)),
-        })
-    }
-
-    fn func(&mut self) -> Result<Definition<'a>> {
-        // func <ident> ($(<ident>: <ty>),*) → <ty> { … }
-        // ^^^^
-
-        let name = self.ident()?;
-
-        // Parameter list
-        let mut params = vec![in self.arena];
-
-        self.require(T!["("])?;
-        let mut next = self.next()?;
-        if next != T![")"] {
-            loop {
-                let Token::Ident(id) = next else {
-                    return Err(self.error(ErrorKind::UnexpectedToken));
-                };
-
-                let id = self.spanned(id);
-                self.require(T![":"])?;
-                params.push((id, self.ty()?));
-
-                match self.next()? {
-                    Token::RightParen => break,
-                    Token::Comma => (),
-                    _ => return Err(self.error(ErrorKind::UnexpectedToken)),
-                }
-
-                next = self.next()?;
-            }
-        }
-
-        self.require(T!["→"])?;
-        let ret = self.ty()?;
-        let body = self.block()?;
-
-        Ok(Definition::Func {
-            name,
-            params: params.into_bump_slice(),
-            ret,
-            body,
-        })
-    }
+pub fn parse_iter(
+    input: impl Iterator<Item = (Token, SimpleSpan)>,
+    eoi: impl Into<SimpleSpan>,
+    arena: &Bump,
+) -> ParseResult {
+    parse_input(Stream::from_iter(input).spanned(eoi.into()), arena)
 }
 
-#[derive(Clone, Copy, Debug, PartialEq, Eq)]
-pub enum ErrorKind {
-    InvalidToken,
-    UnexpectedEnd,
-    UnexpectedToken,
-}
-
-pub type Error = Spanned<ErrorKind>;
-type Result<T, E = Error> = std::result::Result<T, E>;
-
-pub fn parse<'a>(code: &str, arena: &'a Bump) -> Result<&'a [Definition<'a>]> {
-    Parser {
+pub fn parse_lexer(input: Lexer<Token>, arena: &Bump) -> ParseResult {
+    let end = input.span().end;
+    parse_iter(
+        input
+            .spanned()
+            .map(|(token, span)| (token.unwrap_or(Token::Invalid), span.into())),
+        end..end + 1,
         arena,
-        lexer: Token::lexer(code),
-    }
-    .run()
+    )
+}
+
+fn arena_collect<'a, I, O: 'a>(
+    parser: impl IterParser<'a, I, O, Extra<'a>> + Clone,
+) -> impl Parser<'a, I, &'a [O], Extra<'a>> + Clone
+where
+    I: Input<'a, Span = SimpleSpan, Token = Token>,
+{
+    empty()
+        .map_with_state(|_, _, state: &mut State| bumpalo::vec![in state.arena])
+        .foldl(parser, |mut v, o| {
+            v.push(o);
+            v
+        })
+        .map(bumpalo::collections::Vec::into_bump_slice)
+}
+
+fn arena_box<'a, I, O: 'a>(
+    parser: impl Parser<'a, I, O, Extra<'a>> + Clone,
+) -> impl Parser<'a, I, &'a O, Extra<'a>> + Clone
+where
+    I: Input<'a, Span = SimpleSpan, Token = Token>,
+{
+    parser.map_with_state(|item, _, state| &*state.arena.alloc(item))
+}
+
+#[inline]
+fn merge_spans(start: SimpleSpan, end: SimpleSpan) -> SimpleSpan {
+    SimpleSpan::new(start.start, end.end)
 }
diff --git a/src/syntax/token.rs b/src/syntax/token.rs
index 28e6caa..5500f44 100644
--- a/src/syntax/token.rs
+++ b/src/syntax/token.rs
@@ -91,6 +91,8 @@ token_def!(
             "[0-9]+",
             |l| l.slice().parse::<u64>().ok()
         )] Int(u64),
+
+        Invalid,
     }
 );
 
diff --git a/src/utils.rs b/src/utils.rs
index 31a900e..6b4c784 100644
--- a/src/utils.rs
+++ b/src/utils.rs
@@ -2,3 +2,14 @@
 pub fn default<T: Default>() -> T {
     Default::default()
 }
+
+pub trait Pipe {
+    fn pipe<R>(self, mut f: impl FnMut(Self) -> R) -> R
+    where
+        Self: Sized,
+    {
+        f(self)
+    }
+}
+
+impl<T> Pipe for T {}