wip: overcomplicating it on the way to simplifying it ultimately

edn/src/atom.rs

@@ -0,0 +1,10 @@
+use crate::*;
+#[derive(Debug, Copy, Clone, Default, PartialEq)] pub enum AtomType {
+    #[default] Nil, Num, Sym, Key, Exp
+}
+pub trait Atom: Sized + Send + Sync {
+    fn kind (&self) -> TokenKind;
+    fn text (&self) -> &str;
+    fn num (&self) -> usize;
+    fn exp (&self) -> impl Iterator<Item = Self>;
+}

edn/src/atom_arc.rs

@@ -0,0 +1,91 @@
+use crate::*;
+pub type ArcAtomResult = ParseResult<ArcAtom>;
+//const_iter!(|self: ArcAtomIter| => ArcAtom =>
+    //Some(if let Some(token) = Iterator::next(&mut self.0) {
+        //token.to_arc_atom(self.0.0).unwrap()
+    //} else {
+        //return None
+    //}));
+#[derive(Clone, PartialEq)] pub enum ArcAtom {
+    Num(usize),
+    Sym(Arc<str>),
+    Key(Arc<str>),
+    Exp(Vec<ArcAtom>),
+}
+impl ArcAtom {
+    pub fn read_all <'a> (source: &'a str) -> impl Iterator<Item = Result<ArcAtom, ParseError>> + 'a {
+        TokenResultIterator::new(source).map(move |result: TokenResult<'a>|match result{
+            Err(e) => Err(e),
+            Ok(token) => match token.kind() {
+                Nil => Err(ParseError::Empty),
+                Num => match to_number(token.slice_source(source).into()) {
+                    Ok(n) => Ok(ArcAtom::Num(n)),
+                    Err(e) => return Err(e)
+                },
+                Sym => Ok(ArcAtom::Sym(token.slice_source(source).into())),
+                Key => Ok(ArcAtom::Key(token.slice_source(source).into())),
+                Exp => Ok(ArcAtom::Exp({
+                    let mut iter = Self::read_all(token.slice_source(source));
+                    let mut atoms = vec![];
+                    while let Some(atom) = iter.next() {
+                        atoms.push(atom?);
+                    }
+                    atoms
+                }))
+            },
+        })
+    }
+}
+
+impl Atom for ArcAtom {
+    fn kind (&self) -> TokenKind {
+        match self {
+            Self::Num(_) => TokenKind::Num,
+            Self::Sym(_) => TokenKind::Sym,
+            Self::Key(_) => TokenKind::Key,
+            Self::Exp(_) => TokenKind::Exp,
+        }
+    }
+    fn text (&self) -> &str {
+        match self {
+            Self::Num(_)|Self::Exp(_) => "",
+            Self::Sym(s) => s.as_ref(),
+            Self::Key(k) => k.as_ref(),
+        }
+    }
+    fn num (&self) -> usize {
+        match self {
+            Self::Num(n) => *n,
+            _ => 0
+        }
+    }
+    fn exp (&self) -> impl Iterator<Item = ArcAtom> {
+        let cheap_clone = |t: &ArcAtom|t.clone();
+        if let Self::Exp(e) = self {
+            return e.iter().map(cheap_clone)
+        } else {
+            let empty: &[ArcAtom] = &[];
+            empty.iter().map(cheap_clone)
+        }
+    }
+}
+impl<'a> Debug for ArcAtom {
+    fn fmt (&self, f: &mut Formatter<'_>) -> Result<(), FormatError> {
+        match self {
+            Self::Num(n) => write!(f, "(num {n})"),
+            Self::Sym(t) => write!(f, "(sym {t:?})"),
+            Self::Key(t) => write!(f, "(key {t:?})"),
+            Self::Exp(u) => write!(f, "(exp {u:?})"),
+        }
+    }
+}
+impl<'a> Display for ArcAtom {
+    fn fmt (&self, f: &mut Formatter<'_>) -> Result<(), FormatError> {
+        match self {
+            Self::Num(n) => write!(f, "{n}"),
+            Self::Sym(t) => write!(f, "{t}"),
+            Self::Key(t) => write!(f, "{t}"),
+            Self::Exp(u) => write!(f, "({})", join(u.iter().map(|i|format!("{}", &i)), " "))
+        }
+    }
+}

edn/src/atom_ref.rs

@@ -0,0 +1,78 @@
+use crate::*;
+pub type RefAtomResult<'a> = ParseResult<RefAtom<'a>>;
+#[derive(Copy, Clone, PartialEq)] pub struct RefAtomIter<'a>(pub TokenIter<'a>);
+const_iter!(<'a>|self: RefAtomIter<'a>| => RefAtom<'a> =>
+    Some(if let Some(token) = Iterator::next(&mut self.0) {
+        token.to_ref_atom(self.0.0).unwrap()
+    } else {
+        return None
+    }));
+impl<'a> From<&'a str> for RefAtomIter<'a> {
+    fn from (source: &'a str) -> Self { Self::from_source(source) }
+}
+impl<'a> From<TokenIter<'a>> for RefAtomIter<'a> {
+    fn from (iter: TokenIter<'a>) -> Self { Self::from_tokens_iter(iter) }
+}
+impl<'a> RefAtomIter<'a> {
+    pub const fn from_source (source: &'a str) -> Self { Self(TokenIter(source)) }
+    pub const fn from_tokens_iter (iter: TokenIter<'a>) -> Self { Self(iter) }
+}
+#[derive(Copy, Clone, PartialEq)] pub struct RefAtomResultIterator<'a>(pub TokenResultIterator<'a>);
+const_iter!(<'a>|self: RefAtomResultIterator<'a>| => RefAtomResult<'a> =>
+    Some(if let Some(result) = Iterator::next(&mut self.0) {
+        match result { Ok(token) => token.to_ref_atom(self.0.0), Err(e) => Err(e), }
+    } else {
+        return None
+    }));
+impl<'a> From<&'a str> for RefAtomResultIterator<'a> {
+    fn from (source: &'a str) -> Self { Self::from_source(source) }
+}
+impl<'a> From<TokenResultIterator<'a>> for RefAtomResultIterator<'a> {
+    fn from (iter: TokenResultIterator<'a>) -> Self { Self::from_tokens_iter(iter) }
+}
+impl<'a> RefAtomResultIterator<'a> {
+    pub const fn from_source (source: &'a str) -> Self { Self(TokenResultIterator(source)) }
+    pub const fn from_tokens_iter (iter: TokenResultIterator<'a>) -> Self { Self(iter) }
+}
+#[derive(Copy, Clone, PartialEq)] pub enum RefAtom<'a> {
+    Num(usize), Sym(&'a str), Key(&'a str), Exp(RefAtomIter<'a>),
+}
+impl<'a> RefAtom<'a> {
+    pub fn to_arc_atom (&self) -> ArcAtom { todo!() }
+    pub fn read_all <'b: 'a> (source: &'b str) -> impl Iterator<Item = ParseResult<RefAtom<'b>>> + 'b {
+        TokenResultIterator::new(source).map(move |result|match result {
+            Ok(token) => token.to_ref_atom(source), Err(e) => Err(e),
+        })
+    }
+}
+impl<'a> Atom for RefAtom<'a> {
+    fn kind (&self) -> TokenKind {
+        match self {
+            Self::Num(_) => TokenKind::Num,
+            Self::Sym(_) => TokenKind::Sym,
+            Self::Key(_) => TokenKind::Key,
+            Self::Exp(_) => TokenKind::Exp,
+        }
+    }
+    fn text (&self) -> &str {
+        match self {
+            Self::Num(_)|Self::Exp(_) => "",
+            Self::Sym(s) => s,
+            Self::Key(k) => k,
+        }
+    }
+    fn num (&self) -> usize { match self { Self::Num(n) => *n, _ => 0 } }
+    fn exp (&self) -> impl Iterator<Item = RefAtom<'a>> {
+        match self { Self::Exp(e) => *e, _ => RefAtomIter::from("") }
+    }
+}
+impl<'a> Debug for RefAtom<'a> {
+    fn fmt (&self, f: &mut Formatter<'_>) -> Result<(), FormatError> {
+        match self {
+            RefAtom::Num(n) => write!(f, "(num {n})"),
+            RefAtom::Sym(t) => write!(f, "(sym {t:?})"),
+            RefAtom::Key(t) => write!(f, "(key {t:?})"),
+            RefAtom::Exp(u) => write!(f, "(exp {})", join(u.clone().map(|t|format!("{t:?}")), ","))
+        }
+    }
+}

edn/src/context.rs

@@ -0,0 +1,101 @@
+use crate::*;
+/// Map EDN tokens to parameters of a given type for a given context
+pub trait Context<U>: Sized {
+    fn get (&self, _atom: &impl Atom) -> Option<U> {
+        None
+    }
+    fn get_or_fail (&self, atom: &impl Atom) -> U {
+        self.get(atom).expect("no value")
+    }
+}
+impl<T: Context<U>, U> Context<U> for &T {
+    fn get (&self, atom: &impl Atom) -> Option<U> {
+        (*self).get(atom)
+    }
+    fn get_or_fail (&self, atom: &impl Atom) -> U {
+        (*self).get_or_fail(atom)
+    }
+}
+impl<T: Context<U>, U> Context<U> for Option<T> {
+    fn get (&self, atom: &impl Atom) -> Option<U> {
+        self.as_ref().map(|s|s.get(atom)).flatten()
+    }
+    fn get_or_fail (&self, atom: &impl Atom) -> U {
+        self.as_ref().map(|s|s.get_or_fail(atom)).expect("no provider")
+    }
+}
+/// Implement `Context` for a context and type.
+#[macro_export] macro_rules! provide {
+    // Provide a value to the EDN template
+    ($type:ty:|$self:ident:$State:ty|{ $($pat:pat => $expr:expr),* $(,)? }) => {
+        impl Context<$type> for $State {
+            fn get (&$self, atom: &impl Atom) -> Option<$type> {
+                Some(match (atom.kind(), atom.text()) {
+                    $((TokenKind::Sym, $pat) => $expr,)*
+                    _ => return None
+                })
+            }
+        }
+    };
+    // Provide a value more generically
+    ($lt:lifetime: $type:ty:|$self:ident:$State:ty|{ $($pat:pat => $expr:expr),* $(,)? }) => {
+        impl<$lt> Context<$lt, $type> for $State {
+            fn get (&$lt $self, atom: &impl Atom) -> Option<$type> {
+                Some(match (atom.kind(), atom.text()) {
+                    $((TokenKind::Sym, $pat) => $expr,)*
+                    _ => return None
+                })
+            }
+        }
+    };
+}
+/// Implement `Context` for a context and numeric type.
+///
+/// This enables support for numeric literals.
+#[macro_export] macro_rules! provide_num {
+    // Provide a value that may also be a numeric literal in the EDN, to a generic implementation.
+    ($type:ty:|$self:ident:<$T:ident:$Trait:path>|{ $($pat:pat => $expr:expr),* $(,)? }) => {
+        impl<$T: $Trait> Context<$type> for $T {
+            fn get (&$self, atom: &impl Atom) -> Option<$type> {
+                Some(match (atom.kind(), atom.text()) {
+                    $((TokenKind::Sym, $pat) => $expr,)*
+                    (TokenKind::Num, _) => atom.num() as $type,
+                    _ => return None
+                })
+            }
+        }
+    };
+    // Provide a value that may also be a numeric literal in the EDN, to a concrete implementation.
+    ($type:ty:|$self:ident:$State:ty|{ $($pat:pat => $expr:expr),* $(,)? }) => {
+        impl Context<$type> for $State {
+            fn get (&$self, atom: &impl Atom) -> Option<$type> {
+                Some(match (atom.kind(), atom.text()) {
+                    $((TokenKind::Sym, $pat) => $expr,)*
+                    (TokenKind::Num, _) => atom.num() as $type,
+                    _ => return None
+                })
+            }
+        }
+    };
+}
+/// Implement `Context` for a context and content type.
+///
+/// This enables support for layout expressions.
+#[macro_export] macro_rules! provide_content {
+    (|$self:ident:$State:ty|{ $($pat:pat => $expr:expr),* $(,)? }) => {
+        impl<'a, E: Output> Context<'a, Box<dyn Render<E> + 'a>> for $State {
+            fn get (&'a $self, atom: &'a impl Atom) -> Option<Box<dyn Render<E> + 'a>> {
+                use RefAtom::*;
+                Some(match atom.to_ref() { $(RefAtom::Sym($pat) => $expr),*, _ => return None })
+            }
+        }
+    };
+    ($Output:ty: |$self:ident:$State:ty|{ $($pat:pat => $expr:expr),* $(,)? }) => {
+        impl<'a> Context<'a, Box<dyn Render<$Output> + 'a>> for $State {
+            fn get (&'a $self, atom: &'a impl Atom) -> Option<Box<dyn Render<$Output> + 'a>> {
+                use RefAtom::*;
+                Some(match atom.to_ref() { $(Sym($pat) => $expr),*, _ => return None })
+            }
+        }
+    }
+}

edn/src/error.rs

@@ -0,0 +1,21 @@
+use crate::*;
+pub type ParseResult<T> = Result<T, ParseError>;
+#[derive(Debug, Copy, Clone, PartialEq)] pub enum ParseError {
+    Unimplemented,
+    Empty,
+    Incomplete,
+    Unexpected(char), 
+    Code(u8),
+}
+impl Error for ParseError {}
+impl Display for ParseError {
+    fn fmt (&self, f: &mut Formatter) -> FormatResult {
+        match self {
+            Unimplemented => write!(f, "unimplemented"),
+            Empty         => write!(f, "empty"),
+            Incomplete    => write!(f, "incomplete"),
+            Unexpected(c) => write!(f, "unexpected '{c}'"),
+            Code(i)       => write!(f, "error #{i}"),
+        }
+    }
+}

edn/src/lib.rs

@@ -1,8 +1,45 @@
+#![feature(adt_const_params)]
 #![feature(type_alias_impl_trait)]
 #![feature(impl_trait_in_fn_trait_return)]
-mod token; pub use self::token::*;
-pub(crate) use std::fmt::{Debug, Display, Formatter, Error as FormatError};
+mod error;    pub use self::error::*;
+mod token;    pub use self::token::*;
+mod atom;     pub use self::atom::*;
+mod atom_ref; pub use self::atom_ref::*;
+mod atom_arc; pub use self::atom_arc::*;
+mod context;  pub use self::context::*;
+pub(crate) use self::ParseError::*;
+//pub(crate) use self::TokenKind::*;
 pub(crate) use std::sync::Arc;
+//pub(crate) use std::marker::ConstParamTy;
+pub(crate) use itertools::join;
+pub(crate) use konst::iter::{ConstIntoIter, IsIteratorKind};
+pub(crate) use konst::string::{split_at, str_range, char_indices};
+pub(crate) use std::error::Error;
+pub(crate) use std::fmt::{Debug, Display, Formatter, Result as FormatResult, Error as FormatError};
+/// Static iteration helper.
+#[macro_export] macro_rules! iterate {
+    ($expr:expr => $arg: pat => $body:expr) => {
+        let mut iter = $expr;
+        while let Some(($arg, next)) = iter.next() {
+            $body;
+            iter = next;
+        }
+    }
+}
+/// Implement the const iterator pattern.
+#[macro_export] macro_rules! const_iter {
+    ($(<$l:lifetime>)?|$self:ident: $Struct:ty| => $Item:ty => $expr:expr) => {
+        impl$(<$l>)? Iterator for $Struct {
+            type Item = $Item;
+            fn next (&mut $self) -> Option<$Item> { $expr }
+        }
+        impl$(<$l>)? ConstIntoIter for $Struct {
+            type Kind = IsIteratorKind;
+            type Item = $Item;
+            type IntoIter = Self;
+        }
+    }
+}
 #[cfg(test)] #[test] fn test_lang () -> Result<(), ParseError> {
     use Atom::*;
     assert_eq!(Atom::read_all("")?,
@@ -34,14 +71,3 @@ pub(crate) use std::sync::Arc;
     }
     Ok(())
 }
-#[cfg(test)] #[test] fn test_token () -> Result<(), Box<dyn std::error::Error>> {
-    use Token::*;
-    assert_eq!(Nil, Token::chomp_one("")?);
-    assert_eq!(Nil, Token::chomp_one("  \n    \r   \t  ")?);
-    assert_eq!(Num("8", 0, 1), Token::chomp_one("8")?);
-    assert_eq!(Num("   8     ", 3, 1), Token::chomp_one("   8     ")?);
-    assert_eq!(Sym(":foo", 0, 4), Token::chomp_one(":foo")?);
-    assert_eq!(Sym("@bar", 0, 4), Token::chomp_one("@bar")?);
-    assert_eq!(Key("foo/bar", 0, 7), Token::chomp_one("foo/bar")?);
-    Ok(())
-}

edn/src/token.rs

@@ -1,119 +1,41 @@
 use crate::*;
-//use std::iter::IntoIterator;
-use konst::iter::{ConstIntoIter, IsIteratorKind};
-use konst::string::{split_at, str_range, char_indices};
-use itertools::join;
-use self::ParseError::*;
 use self::TokenKind::*;
-#[derive(Debug)] pub enum ParseError {
-    Unimplemented, Empty, Incomplete, Unexpected(char), Code(u8),
+#[derive(Debug, Copy, Clone, Default, PartialEq)] pub struct Token<'a> {
+    source: &'a str,
+    start:  usize, 
+    length: usize,
+    kind:   TokenKind<'a>,
 }
-impl std::fmt::Display for ParseError {
-    fn fmt (&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
-        match self {
-            Unimplemented => write!(f, "unimplemented"),
-            Empty         => write!(f, "empty"),
-            Incomplete    => write!(f, "incomplete"),
-            Unexpected(c) => write!(f, "unexpected '{c}'"),
-            Code(i)       => write!(f, "error #{i}"),
-        }
-    }
+#[derive(Debug, Copy, Clone, Default, PartialEq)] pub enum TokenKind<'a> {
+    #[default] Nil,
+    Err(ParseError),
+    Num(usize),
+    Sym(&'a str),
+    Key(&'a str),
+    Exp(usize, TokenIter<'a>),
 }
-impl std::error::Error for ParseError {}
-macro_rules! iterate {
-    ($expr:expr => $arg: pat => $body:expr) => {
-        let mut iter = $expr;
-        while let Some(($arg, next)) = iter.next() {
-            $body;
-            iter = next;
-        }
-    }
-}
-#[derive(Copy, Clone, PartialEq)] pub struct TokensIterator<'a>(&'a str);
-type TokenResult<'a> = Result<Token<'a>, ParseError>;
-impl<'a> Iterator for TokensIterator<'a> {
-    type Item = TokenResult<'a>;
-    fn next (&mut self) -> Option<TokenResult<'a>> { self.next_mut().map(|(result, _)|result) }
-}
-impl<'a> ConstIntoIter for TokensIterator<'a> {
-    type Kind = IsIteratorKind;
-    type Item = Token<'a>;
-    type IntoIter = Self;
-}
-impl<'a> TokensIterator<'a> {
+#[derive(Copy, Clone, Debug, PartialEq)] pub struct TokenIter<'a>(pub &'a str);
+const_iter!(<'a>|self: TokenIter<'a>| => Token<'a> => self.next_mut().map(|(result, _)|result));
+impl<'a> From<&'a str> for TokenIter<'a> {fn from (source: &'a str) -> Self{Self::new(source)}}
+impl<'a> TokenIter<'a> {
     pub const fn new (source: &'a str) -> Self { Self(source) }
-    pub const fn split (&self, index: usize) -> Self { Self(split_at(self.0, index).1) }
-    pub const fn next (mut self) -> Option<(TokenResult<'a>, Self)> {
-        Self::next_mut(&mut self)
-    }
-    pub const fn next_mut (&mut self) -> Option<(TokenResult<'a>, Self)> {
+    pub const fn chomp (&self, index: usize) -> Self { Self(split_at(self.0, index).1) }
+    pub const fn next (mut self) -> Option<(Token<'a>, Self)> { Self::next_mut(&mut self) }
+    pub const fn peek (&self) -> Option<Token<'a>> { peek_src(self.0) }
+    pub const fn next_mut (&mut self) -> Option<(Token<'a>, Self)> {
         match self.peek() {
-            Some(Ok(token)) => Some((Ok(token), self.split(token.end()))),
-            Some(Err((l, e))) => Some((Err(e), self.split(l))),
+            Some(token) => Some((token, self.chomp(token.end()))),
             None => None
         }
     }
-    pub const fn peek (&self) -> Option<Result<Token<'a>, (usize, ParseError)>> {
-        let mut token: Token<'a> = Token::new(self.0, Nil, 0, 0, 0);
-        iterate!(char_indices(self.0) => (index, c) => token = match token.kind() {
-            Nil => match c {
-                '('                => Token::new(self.0, Exp, index, 1, 1),
-                ':'|'@'            => Token::new(self.0, Sym, index, 1, 0),
-                '0'..='9'          => Token::new(self.0, Num, index, 1, 0),
-                '/'|'a'..='z'      => Token::new(self.0, Key, index, 1, 0),
-                ' '|'\n'|'\r'|'\t' => token.grow(),
-                _ => return Some(Err((token.end(), Unexpected(c))))
-            },
-            Num => match c {
-                '0'..='9' => token.grow(),
-                ' '|'\n'|'\r'|'\t' => return Some(Ok(token)),
-                _ => return Some(Err((token.end(), Unexpected(c))))
-            },
-            Sym => match c {
-                'a'..='z'|'0'..='9'|'-' => token.grow(),
-                ' '|'\n'|'\r'|'\t' => return Some(Ok(token)),
-                _ => return Some(Err((token.end(), Unexpected(c))))
-            },
-            Key => match c {
-                'a'..='z'|'0'..='9'|'-'|'/' => token.grow(),
-                ' '|'\n'|'\r'|'\t' => return Some(Ok(token)),
-                _ => return Some(Err((token.end(), Unexpected(c))))
-            },
-            Exp => match token.depth {
-                0 => return Some(Ok(token)),
-                _ => match c {
-                    ')' => match token.grow_out() {
-                        Ok(token) => token,
-                        Err(e) => return Some(Err((token.end(), e)))
-                    },
-                    '(' => token.grow_in(),
-                     _  => token.grow(),
-                }
-            },
-        });
-        match token.kind() {
-            Nil => None,
-            _ => Some(Err((token.end(), ParseError::Incomplete)))
-        }
-    }
-}
-#[derive(Debug, Copy, Clone, Default, PartialEq)] pub enum TokenKind {
-    #[default] Nil, Num, Sym, Key, Exp
-}
-#[derive(Debug, Copy, Clone, Default, PartialEq)] pub struct Token<'a> {
-    source: &'a str,
-    kind:   TokenKind,
-    start:  usize,
-    length: usize,
-    depth:  usize,
 }
 impl<'a> Token<'a> {
-    pub const fn new (
-        source: &'a str, kind: TokenKind, start: usize, length: usize, depth: usize
-    ) -> Self {
-        Self { source, kind, start, length, depth }
+    pub const fn new (source: &'a str, kind: TokenKind<'a>, start: usize, length: usize) -> Self {
+        Self { source, kind, start, length }
+    }
+    pub const fn end (&self) -> usize {
+        self.start + self.length
     }
-    pub const fn end (&self) -> usize { self.start + self.length }
     pub const fn slice (&'a self) -> &'a str {
         self.slice_source(self.source)
         //str_range(self.source, self.start, self.end())
@@ -121,287 +43,131 @@ impl<'a> Token<'a> {
     pub const fn slice_source <'b> (&'a self, source: &'b str) -> &'b str {
         str_range(source, self.start, self.end())
     }
-    pub const fn kind (&self) -> TokenKind { Nil }
+    pub const fn kind (&self) -> TokenKind {
+        self.kind
+    }
+    pub const fn error (self, error: ParseError) -> Self {
+        Self { kind: TokenKind::Err(error), ..self }
+    }
     pub const fn grow (self) -> Self {
         Self { length: self.length + 1, ..self }
     }
     pub const fn grow_in (self) -> Self {
-        Self { length: self.length + 1, depth: self.depth + 1, ..self }
-    }
-    pub const fn grow_out (self) -> Result<Self, ParseError> {
-        match self.depth {
-            0 => Err(Unexpected(')')),
-            d => Ok(Self { length: self.length + 1, depth: d - 1, ..self })
-        }
-    }
-    pub const fn to_ref_atom (&self, source: &'a str) -> Result<RefAtom<'a>, ParseError> {
+        //Self { length: self.length + 1, depth: self.depth + 1, ..self };
         match self.kind {
-            Nil => Err(ParseError::Empty),
-            Num => match to_number(self.slice_source(source)) {
-                Err(e) => Err(e),
-                Ok(n) => Ok(RefAtom::Num(n)),
+            TokenKind::Exp(depth, source) => Self {
+                kind: TokenKind::Exp(depth + 1, TokenIter(self.grow().slice_source(source.0))),
+                ..self.grow()
             },
-            Sym => Ok(RefAtom::Sym(self.slice_source(source))),
-            Key => Ok(RefAtom::Key(self.slice_source(source))),
-            Exp => Ok(
-                RefAtom::Exp(RefAtomsIterator(TokensIterator::new(self.slice_source(source))))
-            )
+            _ => self.grow()
         }
     }
+    pub const fn grow_out (self) -> Self {
+        match self.kind {
+            TokenKind::Exp(depth, source) => match depth {
+                0 => self.error(Unexpected(')')),
+                d => Self {
+                    kind: TokenKind::Exp(d - 1, TokenIter(self.grow().slice_source(source.0))),
+                    ..self.grow()
+                }
+            },
+            _ => self.grow()
+        }
+    }
+    //pub const fn to_ref_atom (&self, source: &'a str) -> RefAtom<'a> {
+        //match self.kind {
+            //TokenKind::Nil => Err(ParseError::Empty),
+            //TokenKind::Num => match to_number(self.slice_source(source)) {
+                //Err(e) => Err(e),
+                //Ok(n) => Ok(RefAtom::Num(n)),
+            //},
+            //TokenKind::Sym => Ok(RefAtom::Sym(self.slice_source(source))),
+            //TokenKind::Key => Ok(RefAtom::Key(self.slice_source(source))),
+            //TokenKind::Exp => Ok(
+                //RefAtom::Exp(RefAtomIterator(TokenIter::new(self.slice_source(source))))
+            //)
+        //}
+    //}
+}
+pub const fn peek_src <'a> (source: &'a str) -> Option<Token<'a>> {
+    let mut token: Token<'a> = Token::new(source, Nil, 0, 0);
+    iterate!(char_indices(source) => (start, c) => token = match token.kind() {
+        Err(_) => return Some(token),
+        Nil => match c {
+            ' '|'\n'|'\r'|'\t' => token.grow(),
+            '(' => Token {
+                source, start, length: 1,
+                kind: TokenKind::Exp(1, TokenIter(str_range(source, start, start + 1))),
+            },
+            '0'..='9' => Token {
+                source, start, length: 1,
+                kind: match to_digit(c) {
+                    Ok(c) => TokenKind::Num(c),
+                    Result::Err(e) => TokenKind::Err(e)
+                }
+            },
+            ':'|'@' => Token {
+                source, start, length: 1,
+                kind: TokenKind::Sym(str_range(source, start, start + 1)),
+            },
+            '/'|'a'..='z' => Token {
+                source, start, length: 1,
+                kind: TokenKind::Key(str_range(source, start, start + 1)),
+            },
+            _ => token.error(Unexpected(c))
+        },
+        Num(_) => match c {
+            '0'..='9' => token.grow(),
+            ' '|'\n'|'\r'|'\t' => return Some(token),
+            _ => token.error(Unexpected(c))
+        },
+        Sym(_) => match c {
+            'a'..='z'|'0'..='9'|'-' => token.grow(),
+            ' '|'\n'|'\r'|'\t' => return Some(token),
+            _ => token.error(Unexpected(c))
+        },
+        Key(_) => match c {
+            'a'..='z'|'0'..='9'|'-'|'/' => token.grow(),
+            ' '|'\n'|'\r'|'\t' => return Some(token),
+            _ => token.error(Unexpected(c))
+        },
+        Exp(depth, _) => match depth {
+            0 => return Some(token),
+            _ => match c {
+                ')' => token.grow_out(),
+                '(' => token.grow_in(),
+                 _  => token.grow(),
+            }
+        },
+    });
+    match token.kind() {
+        Nil => None,
+        _ => Some(token),
+    }
 }
-const fn to_number (digits: &str) -> Result<usize, ParseError> {
+pub const fn to_number (digits: &str) -> Result<usize, ParseError> {
     let mut value = 0;
     iterate!(char_indices(digits) => (_, c) => match to_digit(c) {
         Ok(digit) => value = 10 * value + digit,
-        Err(e) => return Err(e)
+        Result::Err(e) => return Result::Err(e)
     });
     Ok(value)
 }
-const fn to_digit (c: char) -> Result<usize, ParseError> {
+pub const fn to_digit (c: char) -> Result<usize, ParseError> {
     Ok(match c {
         '0' => 0, '1' => 1, '2' => 2, '3' => 3, '4' => 4,
         '5' => 5, '6' => 6, '7' => 7, '8' => 8, '9' => 9,
-        _ => return Err(Unexpected(c))
+        _ => return Result::Err(Unexpected(c))
     })
 }
-pub trait Atom: Sized + Send + Sync {
-    fn kind (&self) -> TokenKind;
-    fn text (&self) -> &str;
-    fn num  (&self) -> usize;
-}
-#[derive(Copy, Clone, PartialEq)] pub enum RefAtom<'a> {
-    Num(usize),
-    Sym(&'a str),
-    Key(&'a str),
-    Exp(RefAtomsIterator<'a>),
-}
-type RefAtomResult<'a> = Result<RefAtom<'a>, ParseError>;
-#[derive(Copy, Clone, PartialEq)] pub struct RefAtomsIterator<'a>(TokensIterator<'a>);
-impl<'a> Iterator for RefAtomsIterator<'a> {
-    type Item = RefAtomResult<'a>;
-    fn next (&mut self) -> Option<RefAtomResult<'a>> {
-        Some(if let Some(result) = Iterator::next(&mut self.0) {
-            match result { Ok(token) => token.to_ref_atom(self.0.0), Err(e) => Err(e), }
-        } else {
-            return None
-        })
-    }
-}
-impl<'a> RefAtom<'a> {
-    pub fn to_arc_atom (&self) -> ArcAtom {
-        todo!()
-    }
-    pub fn read_all <'b: 'a> (source: &'b str)
-        -> impl Iterator<Item = Result<RefAtom<'b>, ParseError>> + 'b
-    {
-        TokensIterator::new(source).map(move |result|match result {
-            Ok(token) => token.to_ref_atom(source), Err(e) => Err(e),
-        })
-    }
-}
-impl<'a> Atom for RefAtom<'a> {
-    fn kind (&self) -> TokenKind {
-        match self {
-            Self::Num(_) => TokenKind::Num,
-            Self::Sym(_) => TokenKind::Sym,
-            Self::Key(_) => TokenKind::Key,
-            Self::Exp(_) => TokenKind::Exp,
-        }
-    }
-    fn text (&self) -> &str {
-        match self {
-            Self::Num(_)|Self::Exp(_) => "",
-            Self::Sym(s) => s,
-            Self::Key(k) => k,
-        }
-    }
-    fn num (&self) -> usize {
-        match self {
-            Self::Num(n) => *n,
-            _ => 0
-        }
-    }
-}
-impl<'a> Debug for RefAtom<'a> {
-    fn fmt (&self, f: &mut Formatter<'_>) -> Result<(), FormatError> {
-        match self {
-            RefAtom::Num(n) => write!(f, "(num {n})"),
-            RefAtom::Sym(t) => write!(f, "(sym {t:?})"),
-            RefAtom::Key(t) => write!(f, "(key {t:?})"),
-            RefAtom::Exp(u) => write!(f, "(exp {})", join(u.clone().map(|t|format!("{t:?}")), ","))
-        }
-    }
-}
-#[derive(Clone, PartialEq)] pub enum ArcAtom {
-    Num(usize),
-    Sym(Arc<str>),
-    Key(Arc<str>),
-    Exp(Vec<ArcAtom>),
-}
-impl ArcAtom {
-    pub fn read_all <'a> (source: &'a str) -> impl Iterator<Item = Result<ArcAtom, ParseError>> + 'a {
-        TokensIterator::new(source).map(move |result: TokenResult<'a>|match result{
-            Err(e) => Err(e),
-            Ok(token) => match token.kind {
-                Nil => Err(ParseError::Empty),
-                Num => match to_number(token.slice_source(source).into()) {
-                    Ok(n) => Ok(ArcAtom::Num(n)),
-                    Err(e) => return Err(e)
-                },
-                Sym => Ok(ArcAtom::Sym(token.slice_source(source).into())),
-                Key => Ok(ArcAtom::Key(token.slice_source(source).into())),
-                Exp => Ok(ArcAtom::Exp({
-                    let mut iter = Self::read_all(token.slice_source(source));
-                    let mut atoms = vec![];
-                    while let Some(atom) = iter.next() {
-                        atoms.push(atom?);
-                    }
-                    atoms
-                }))
-            },
-        })
-    }
-}
-impl<'a> Atom for ArcAtom {
-    fn kind (&self) -> TokenKind {
-        match self {
-            Self::Num(_) => TokenKind::Num,
-            Self::Sym(_) => TokenKind::Sym,
-            Self::Key(_) => TokenKind::Key,
-            Self::Exp(_) => TokenKind::Exp,
-        }
-    }
-    fn text (&self) -> &str {
-        match self {
-            Self::Num(_)|Self::Exp(_) => "",
-            Self::Sym(s) => s.as_ref(),
-            Self::Key(k) => k.as_ref(),
-        }
-    }
-    fn num (&self) -> usize {
-        match self {
-            Self::Num(n) => *n,
-            _ => 0
-        }
-    }
-}
-impl<'a> Debug for ArcAtom {
-    fn fmt (&self, f: &mut Formatter<'_>) -> Result<(), FormatError> {
-        match self {
-            Self::Num(n) => write!(f, "(num {n})"),
-            Self::Sym(t) => write!(f, "(sym {t:?})"),
-            Self::Key(t) => write!(f, "(key {t:?})"),
-            Self::Exp(u) => write!(f, "(exp {u:?})"),
-        }
-    }
-}
-impl<'a> Display for ArcAtom {
-    fn fmt (&self, f: &mut Formatter<'_>) -> Result<(), FormatError> {
-        match self {
-            Self::Num(n) => write!(f, "{n}"),
-            Self::Sym(t) => write!(f, "{t}"),
-            Self::Key(t) => write!(f, "{t}"),
-            Self::Exp(u) => write!(f, "({})", join(u.iter().map(|i|format!("{}", &i)), " "))
-        }
-    }
-}
-/// Map EDN tokens to parameters of a given type for a given context
-pub trait Context<U>: Sized {
-    fn get (&self, _atom: &impl Atom) -> Option<U> {
-        None
-    }
-    fn get_or_fail (&self, atom: &impl Atom) -> U {
-        self.get(atom).expect("no value")
-    }
-}
-impl<T: Context<U>, U> Context<U> for &T {
-    fn get (&self, atom: &impl Atom) -> Option<U> {
-        (*self).get(atom)
-    }
-    fn get_or_fail (&self, atom: &impl Atom) -> U {
-        (*self).get_or_fail(atom)
-    }
-}
-impl<T: Context<U>, U> Context<U> for Option<T> {
-    fn get (&self, atom: &impl Atom) -> Option<U> {
-        self.as_ref().map(|s|s.get(atom)).flatten()
-    }
-    fn get_or_fail (&self, atom: &impl Atom) -> U {
-        self.as_ref().map(|s|s.get_or_fail(atom)).expect("no provider")
-    }
-}
-/// Implement `Context` for a context and type.
-#[macro_export] macro_rules! provide {
-    // Provide a value to the EDN template
-    ($type:ty:|$self:ident:$State:ty|{ $($pat:pat => $expr:expr),* $(,)? }) => {
-        impl Context<$type> for $State {
-            fn get (&$self, atom: &impl Atom) -> Option<$type> {
-                Some(match (atom.kind(), atom.text()) {
-                    $((TokenKind::Sym, $pat) => $expr,)*
-                    _ => return None
-                })
-            }
-        }
-    };
-    // Provide a value more generically
-    ($lt:lifetime: $type:ty:|$self:ident:$State:ty|{ $($pat:pat => $expr:expr),* $(,)? }) => {
-        impl<$lt> Context<$lt, $type> for $State {
-            fn get (&$lt $self, atom: &impl Atom) -> Option<$type> {
-                Some(match (atom.kind(), atom.text()) {
-                    $((TokenKind::Sym, $pat) => $expr,)*
-                    _ => return None
-                })
-            }
-        }
-    };
-}
-/// Implement `Context` for a context and numeric type.
-///
-/// This enables support for numeric literals.
-#[macro_export] macro_rules! provide_num {
-    // Provide a value that may also be a numeric literal in the EDN, to a generic implementation.
-    ($type:ty:|$self:ident:<$T:ident:$Trait:path>|{ $($pat:pat => $expr:expr),* $(,)? }) => {
-        impl<$T: $Trait> Context<$type> for $T {
-            fn get (&$self, atom: &impl Atom) -> Option<$type> {
-                Some(match (atom.kind(), atom.text()) {
-                    $((TokenKind::Sym, $pat) => $expr,)*
-                    (TokenKind::Num, _) => atom.num() as $type,
-                    _ => return None
-                })
-            }
-        }
-    };
-    // Provide a value that may also be a numeric literal in the EDN, to a concrete implementation.
-    ($type:ty:|$self:ident:$State:ty|{ $($pat:pat => $expr:expr),* $(,)? }) => {
-        impl Context<$type> for $State {
-            fn get (&$self, atom: &impl Atom) -> Option<$type> {
-                Some(match (atom.kind(), atom.text()) {
-                    $((TokenKind::Sym, $pat) => $expr,)*
-                    (TokenKind::Num, _) => atom.num() as $type,
-                    _ => return None
-                })
-            }
-        }
-    };
-}
-/// Implement `Context` for a context and content type.
-///
-/// This enables support for layout expressions.
-#[macro_export] macro_rules! provide_content {
-    (|$self:ident:$State:ty|{ $($pat:pat => $expr:expr),* $(,)? }) => {
-        impl<'a, E: Output> Context<'a, Box<dyn Render<E> + 'a>> for $State {
-            fn get (&'a $self, atom: &'a impl Atom) -> Option<Box<dyn Render<E> + 'a>> {
-                use RefAtom::*;
-                Some(match atom.to_ref() { $(RefAtom::Sym($pat) => $expr),*, _ => return None })
-            }
-        }
-    };
-    ($Output:ty: |$self:ident:$State:ty|{ $($pat:pat => $expr:expr),* $(,)? }) => {
-        impl<'a> Context<'a, Box<dyn Render<$Output> + 'a>> for $State {
-            fn get (&'a $self, atom: &'a impl Atom) -> Option<Box<dyn Render<$Output> + 'a>> {
-                use RefAtom::*;
-                Some(match atom.to_ref() { $(Sym($pat) => $expr),*, _ => return None })
-            }
-        }
-    }
+#[cfg(test)] #[test] fn test_token () -> Result<(), Box<dyn std::error::Error>> {
+    use Token::*;
+    assert_eq!(Nil, Token::chomp_one("")?);
+    assert_eq!(Nil, Token::chomp_one("  \n    \r   \t  ")?);
+    assert_eq!(Num("8", 0, 1), Token::chomp_one("8")?);
+    assert_eq!(Num("   8     ", 3, 1), Token::chomp_one("   8     ")?);
+    assert_eq!(Sym(":foo", 0, 4), Token::chomp_one(":foo")?);
+    assert_eq!(Sym("@bar", 0, 4), Token::chomp_one("@bar")?);
+    assert_eq!(Key("foo/bar", 0, 7), Token::chomp_one("foo/bar")?);
+    Ok(())
 }