diff --git a/dsl/src/dsl.rs b/dsl/src/dsl.rs
index e8aad19..f57c8ce 100644
--- a/dsl/src/dsl.rs
+++ b/dsl/src/dsl.rs
@@ -1,494 +1,58 @@
-#![feature(adt_const_params)]
-#![feature(type_alias_impl_trait)]
+//#![feature(adt_const_params)]
+//#![feature(type_alias_impl_trait)]
 #![feature(impl_trait_in_fn_trait_return)]
 #![feature(const_precise_live_drops)]
 extern crate const_panic;
-use const_panic::{concat_panic, PanicFmt};
+use const_panic::PanicFmt;
+use std::fmt::Debug;
 pub(crate) use ::tengri_core::*;
-use std::ops::Deref;
 pub(crate) use std::error::Error;
-pub(crate) use std::fmt::Debug;
 pub(crate) use std::sync::Arc;
-pub(crate) use std::collections::VecDeque;
-pub(crate) use konst::iter::{ConstIntoIter, IsIteratorKind};
-pub(crate) use konst::string::{split_at, str_range, char_indices};
+pub(crate) use konst::string::{str_range, char_indices};
 pub(crate) use thiserror::Error;
 pub(crate) use self::DslError::*;
+
+mod dsl_conv;  pub use self::dsl_conv::*;
+mod dsl_types; pub use self::dsl_types::*;
 #[cfg(test)] mod dsl_test;
 
-#[macro_export] macro_rules! dsl_read_advance (($exp:ident, $pat:pat => $val:expr)=>{{
-    let (head, tail) = $exp.advance(); $exp = tail; match head {
-        Some($pat) => Ok($val), _ => Err(format!("(e4) unexpected {head:?}").into()) }}});
-
-/// Coerce to [Val] for predefined [Self::Str] and [Self::Exp].
-pub trait Dsl: Clone + Debug {
-    /// The string representation for a dizzle.
-    type Str: DslStr;
-    /// The string representation for a dizzle.
-    type Exp: DslExp;
-    /// Request the top-level DSL [Val]ue.
-    /// May perform cloning or parsing.
-    fn val     (&self) -> Val<Self::Str, Self::Exp>;
-    fn err     (&self) -> Option<DslError>           {self.val().err()}
-    fn nil     (&self) -> bool                       {self.val().nil()}
-    fn num     (&self) -> Option<usize>              {self.val().num()}
-    fn sym     (&self) -> Option<Self::Str>          {self.val().sym()}
-    fn key     (&self) -> Option<Self::Str>          {self.val().key()}
-    fn str     (&self) -> Option<Self::Str>          {self.val().str()}
-    fn exp     (&self) -> Option<Self::Exp>          {self.val().exp()}
-    fn depth   (&self) -> Option<isize>              {self.val().depth()}
-    fn head    (&self) -> Val<Self::Str, Self::Exp>  {self.val().head()}
-    fn tail    (&self) -> Self::Exp                  {self.val().tail()}
-    fn advance (&self) -> (Val<Self::Str, Self::Exp>, Self::Exp) { (self.head(), self.tail()) }
-    fn each    (&self, f: impl Fn(&Self) -> Usually<()>) -> Usually<()> { todo!() }
-    fn exp_next (&mut self) -> Option<Val<Self::Str, Self::Exp>> { todo!() }
+pub trait Dsl: Debug + Send + Sync + Sized {
+    fn src (&self) -> &str;
 }
+
 impl<'s> Dsl for &'s str {
-    type Str = &'s str;
-    type Exp = &'s str;
-    fn val (&self) -> Val<Self::Str, Self::Exp> { Val::Exp(0, self) }
-}
-impl<'s> Dsl for Cst<'s> {
-    type Str = &'s str;
-    type Exp = Cst<'s>;
-    fn val (&self) -> Val<Self::Str, Self::Exp> { Val::Exp(0, *self) }
-}
-impl Dsl for Ast {
-    type Str = Arc<str>;
-    type Exp = Ast;
-    fn val (&self) -> Val<Self::Str, Ast> { Val::Exp(0, self.clone()) }
-}
-impl<Str: DslStr, Exp: DslExp> Dsl for Token<Str, Exp> {
-    type Str = Str;
-    type Exp = Exp;
-    fn val (&self) -> Val<Str, Exp> { self.value.clone() }
-}
-impl<Str: DslStr, Exp: DslExp> Dsl for Val<Str, Exp> {
-    type Str = Str;
-    type Exp = Exp;
-    fn val (&self) -> Val<Str, Exp> { self.clone() }
+    fn src (&self) -> &str { self }
 }
 
-/// The expression representation for a [Dsl] implementation.
-/// [Cst] uses [CstIter]. [Ast] uses [VecDeque].
-pub trait DslExp: PartialEq + Clone + Debug + Dsl {}
-impl<T: PartialEq + Clone + Debug + Dsl> DslExp for T {}
-/// The string representation for a [Dsl] implementation.
-/// [Cst] uses `&'s str`. [Ast] uses `Arc<str>`.
-pub trait DslStr: PartialEq + Clone + Default + Debug + AsRef<str> + Deref<Target = str> {
-    fn as_str (&self) -> &str     { self.as_ref() }
-    fn as_arc (&self) -> Arc<str> { self.as_ref().into() }
+impl Dsl for std::sync::Arc<str> {
+    fn src (&self) -> &str { self.as_ref() }
 }
-impl<Str: PartialEq + Clone + Default + Debug + AsRef<str> + Deref<Target = str>> DslStr for Str {}
-/// Enumeration of values that may figure in an expression.
-/// Generic over string and expression storage.
-#[derive(Clone, Debug, PartialEq, Default)]
-pub enum Val<Str, Exp> {
-    /// Empty expression
-    #[default] Nil,
-    /// Unsigned integer literal
-    Num(usize),
-    /// An identifier that starts with `.`
-    Sym(Str),
-    /// An identifier that doesn't start with `:`
-    Key(Str),
-    /// A quoted string literal
-    Str(Str),
-    /// A DSL expression.
-    Exp(
-        /// Number of unclosed parentheses. Must be 0 to be valid.
-        isize,
-        /// Expression content.
-        Exp
-    ),
-    /// An error.
-    Error(DslError),
+
+impl<D: Dsl> Dsl for Option<D> {
+    fn src (&self) -> &str { if let Some(dsl) = self { dsl.src() } else { "" } }
 }
-impl<Str: Copy, Exp: Copy> Copy for Val<Str, Exp> {}
-impl<S1, E1> Val<S1, E1> {
-    pub fn convert_to <S2, E2> (&self, to_str: impl Fn(&S1)->S2, to_exp: impl Fn(&E1)->E2) -> Val<S2, E2> {
-        match self {
-            Val::Nil       => Val::Nil,
-            Val::Num(u)    => Val::Num(*u),
-            Val::Sym(s)    => Val::Sym(to_str(s)),
-            Val::Key(s)    => Val::Key(to_str(s)),
-            Val::Str(s)    => Val::Str(to_str(s)),
-            Val::Exp(d, x) => Val::Exp(*d, to_exp(x)),
-            Val::Error(e)  => Val::Error(*e)
-        }
-    }
+
+impl<D: Dsl> Dsl for &D {
+    fn src (&self) -> &str { (*self).src() }
 }
-impl<Str: DslStr, Exp: DslExp + Dsl<Str=Str>> Val<Str, Exp> {
-    pub const fn err (&self)       -> Option<DslError> {match self{Val::Error(e)=>Some(*e),        _=>None}}
-    pub const fn nil (&self)       -> bool             {match self{Val::Nil=>true,                 _=>false}}
-    pub const fn num (&self)       -> Option<usize>    {match self{Val::Num(n)=>Some(*n),          _=>None}}
-    pub const fn sym (&self)       -> Option<&Str>     {match self{Val::Sym(s)=>Some(s),   _=>None}}
-    pub const fn key (&self)       -> Option<&Str>     {match self{Val::Key(k)=>Some(k),   _=>None}}
-    pub const fn str (&self)       -> Option<&Str>     {match self{Val::Str(s)=>Some(s),   _=>None}}
-    pub const fn exp (&self)       -> Option<&Exp>     {match self{Val::Exp(_, x)=>Some(x),_=>None}}
-    pub const fn depth (&self) -> Option<isize>    {match self{Val::Exp(d, _)=>Some(*d),       _=>None}}
+
+impl<D: Dsl> Dsl for &mut D {
+    fn src (&self) -> &str { (**self).src() }
 }
-/// Parsed substring with range and value.
-#[derive(Debug, Clone, Default, PartialEq)]
-pub struct Token<Str, Exp> {
-    /// Meaning of token.
-    pub value: Val<Str, Exp>,
-    /// Reference to source text.
-    pub source: Str,
-    /// Index of 1st character of span.
-    pub start:  usize,
-    /// Length of span.
-    pub length: usize,
-}
-/// Tokens are copiable where possible.
-impl<Str: Copy, Exp: Copy> Copy for Token<Str, Exp> {}
-/// Token methods.
-impl<Str, Exp> Token<Str, Exp> {
-    pub const fn end (&self) -> usize {
-        self.start.saturating_add(self.length) }
-    pub const fn value (&self)
-        -> &Val<Str, Exp> { &self.value }
-    pub const fn err (&self)
-        -> Option<DslError> { if let Val::Error(e) = self.value { Some(e) } else { None } }
-    pub const fn new (source: Str, start: usize, length: usize, value: Val<Str, Exp>)
-        -> Self { Self { value, start, length, source } }
-    pub const fn copy (&self) -> Self where Val<Str, Exp>: Copy, Str: Copy, Exp: Copy {
-        Self { value: self.value, ..*self }
-    }
-}
-/// The concrete syntax tree (CST) implements zero-copy
-/// parsing of the DSL from a string reference. CST items
-/// preserve info about their location in the source.
-/// CST stores strings as source references and expressions as [CstIter] instances.
-#[derive(Debug, Copy, Clone, PartialEq, Default)]
-pub enum Cst<'s> {
-    #[default] __,
-    Source(&'s str),
-    Token(CstToken<'s>),
-    Val(CstVal<'s>),
-    Iter(CstIter<'s>),
-    ConstIter(CstConstIter<'s>),
-}
-impl<'s> From<&'s str> for Cst<'s> {
-    fn from (src: &'s str) -> Self {
-        Cst::Source(src)
-    }
-}
-impl<'s> From<CstToken<'s>> for Cst<'s> {
-    fn from (token: CstToken<'s>) -> Self {
-        Cst::Token(token)
-    }
-}
-impl<'s> From<CstVal<'s>> for Cst<'s> {
-    fn from (val: CstVal<'s>) -> Self {
-        Cst::Val(val)
-    }
-}
-impl<'s> From<CstIter<'s>> for Cst<'s> {
-    fn from (iter: CstIter<'s>) -> Self {
-        Cst::Iter(iter)
-    }
-}
-impl<'s> From<CstConstIter<'s>> for Cst<'s> {
-    fn from (iter: CstConstIter<'s>) -> Self {
-        Cst::ConstIter(iter)
-    }
-}
-impl<'s> From<Cst<'s>> for Ast {
-    fn from (cst: Cst<'s>) -> Self {
-        match cst {
-            Cst::Source(source) | Cst::Iter(CstIter(CstConstIter(source))) |
-            Cst::ConstIter(CstConstIter(source)) =>
-                Ast::Source(source.into()),
-            Cst::Val(value) =>
-                Ast::Val(value.convert_to(|s|(*s).into(), |e|Box::new((*e).into()))),
-            Cst::Token(Token { source, start, length, value }) => {
-                let source = AsRef::<str>::as_ref(source).into();
-                let value  = value.convert_to(|s|(*s).into(), |e|Box::new((*e).into()));
-                Ast::Token(Token { source, start, length, value })
-            },
-            _ => unreachable!()
-        }
-    }
-}
-/// The abstract syntax tree (AST) can be produced from the CST
-/// by cloning source slices into owned ([Arc]) string slices.
-#[derive(Debug, Clone, PartialEq, Default)]
-pub enum Ast {
-    #[default] __,
-    Source(Arc<str>),
-    Token(Token<Arc<str>, Box<Ast>>),
-    Val(Val<Arc<str>, Box<Ast>>),
-    Exp(Arc<VecDeque<Arc<Token<Arc<str>, Ast>>>>),
-}
-impl<'s> From<&'s str> for Ast {
-    fn from (src: &'s str) -> Self {
-        Self::Source(src.into())
-    }
-}
-impl<'s, Str: DslStr, Exp: DslExp + Into<Ast> + 's> From<Token<Str, Exp>> for Ast {
-    fn from (Token { source, start, length, value }: Token<Str, Exp>) -> Self {
-        let source: Arc<str> = source.as_ref().into();
-        let value = value.convert_to(|s|s.as_ref().into(), |e|Box::new(e.clone().into()));
-        Self::Token(Token { source, start, length, value })
-    }
-}
-pub type CstVal<'s> = Val<&'s str, &'s str>;
-pub type CstToken<'s> = Token<&'s str, &'s str>;
-impl<'s> CstToken<'s> {
-    pub const fn slice (&self) -> &str {
-        str_range(self.source, self.start, self.end()) }
-    pub const fn slice_exp (&self) -> &str {
-        str_range(self.source, self.start.saturating_add(1), self.end()) }
-    pub const fn grow (&mut self) -> &mut Self {
-        let max_length = self.source.len().saturating_sub(self.start);
-        self.length    = self.length + 1;
-        if self.length > max_length { self.length = max_length }
-        self
-    }
-    pub const fn grow_exp (&'s mut self, depth: isize, source: &'s str) -> &mut Self {
-        self.value = Val::Exp(depth, source);
-        self
-    }
-}
-//impl<'s> From<&'s str> for Ast {
-    //fn from (source: &'s str) -> Ast {
-        //let source: Arc<str> = source.into();
-        //Ast(CstIter(CstConstIter(source.as_ref()))
-            //.map(|token|Arc::new(Token {
-                //source: source.clone(),
-                //start:  token.start,
-                //length: token.length,
-                //value:  match token.value {
-                    //Val::Nil       => Val::Nil,
-                    //Val::Num(u)    => Val::Num(u),
-                    //Val::Sym(s)    => Val::Sym(s.into()),
-                    //Val::Key(s)    => Val::Key(s.into()),
-                    //Val::Str(s)    => Val::Str(s.into()),
-                    //Val::Exp(d, x) => Val::Exp(d, x.into()),
-                    //Val::Error(e)  => Val::Error(e.into())
-                //},
-            //}))
-            //.collect::<VecDeque<_>>()
-            //.into())
-    //}
-//}
+
+/// DSL-specific result type.
+pub type DslResult<T> = Result<T, DslError>;
+
+/// DSL-specific optional result type.
+pub type DslPerhaps<T> = Result<Option<T>, DslError>;
+
 /// DSL-specific error codes.
-#[derive(Error, Debug, Copy, Clone, PartialEq, PanicFmt)] pub enum DslError {
-    #[error("parse failed: not implemented")]
-    Unimplemented,
-    #[error("parse failed: empty")]
-    Empty,
-    #[error("parse failed: incomplete")]
-    Incomplete,
-    #[error("parse failed: unexpected character '{0}'")]
-    Unexpected(char),
-    #[error("parse failed: error #{0}")]
-    Code(u8),
-    #[error("end reached")]
-    End
-}
-/// Provides native [Iterator] API over [CstConstIter], emitting [Cst] items.
-///
-/// [Cst::next] returns just the [Cst] and mutates `self`,
-/// instead of returning an updated version of the struct as [CstConstIter::next] does.
-#[derive(Copy, Clone, Debug, Default, PartialEq)]
-pub struct CstIter<'s>(pub CstConstIter<'s>);
-impl<'s> CstIter<'s> {
-    pub const fn new (source: &'s str) -> Self { Self(CstConstIter::new(source)) }
-}
-impl<'s> Iterator for CstIter<'s> {
-    type Item = CstToken<'s>;
-    fn next (&mut self) -> Option<Self::Item> {
-        match self.0.advance() {
-            Some((item, rest)) => { self.0 = rest; Some(item.into()) },
-            None => None,
-        }
-    }
-}
-/// Holds a reference to the source text.
-/// [CstConstIter::next] emits subsequent pairs of:
-/// * a [Cst] and
-/// * the source text remaining
-///   * [ ] TODO: maybe [CstConstIter::next] should wrap the remaining source in `Self` ?
-#[derive(Copy, Clone, Debug, Default, PartialEq)]
-pub struct CstConstIter<'s>(pub &'s str);
-impl<'s> From <&'s str> for CstConstIter<'s> {
-    fn from (src: &'s str) -> Self { Self(src) }
-}
-impl<'s> Iterator for CstConstIter<'s> {
-    type Item = CstToken<'s>;
-    fn next (&mut self) -> Option<CstToken<'s>> { self.advance().map(|x|x.0) }
-}
-impl<'s> ConstIntoIter for CstConstIter<'s> {
-    type Kind = IsIteratorKind;
-    type Item = Cst<'s>;
-    type IntoIter = Self;
-}
-impl<'s> CstConstIter<'s> {
-    pub const fn new (source: &'s str) -> Self { Self(source) }
-    pub const fn chomp (&self, index: usize) -> Self { Self(split_at(self.0, index).1) }
-    pub const fn advance (&mut self) -> Option<(CstToken<'s>, Self)> {
-        match peek(Val::Nil, self.0) {
-            Token { value: Val::Nil, .. } => None,
-            token => {
-                let end = self.chomp(token.end());
-                Some((token.copy(), end))
-            },
-        }
-    }
-}
-
-pub const fn peek <'s> (mut value: CstVal<'s>, source: &'s str) -> CstToken<'s> {
-    use Val::*;
-    let mut start  = 0;
-    let mut length = 0;
-    let mut source = source;
-    loop {
-        if let Some(((i, c), next)) = char_indices(source).next() {
-            if matches!(value, Error(_)) {
-                break
-            } else if matches!(value, Nil) {
-                if is_whitespace(c) {
-                    length += 1;
-                    continue
-                }
-                start  = i;
-                length = 1;
-                value  = if is_exp_start(c) { Exp(1, str_range(source, i, i+1)) }
-                    else if is_str_start(c) { Str(str_range(source, i, i+1))    }
-                    else if is_sym_start(c) { Sym(str_range(source, i, i+1))    }
-                    else if is_key_start(c) { Key(str_range(source, i, i+1))    }
-                    else if is_digit(c) { match to_digit(c) { Ok(c) => Num(c), Err(e) => Error(e) } }
-                    else { value = Error(Unexpected(c)); break }
-            } else if matches!(value, Str(_)) {
-                if is_str_end(c) {
-                    break
-                } else {
-                    value = Str(str_range(source, start, start + length + 1));
-                }
-            } else if matches!(value, Sym(_)) {
-                if is_sym_end(c) {
-                    break
-                } else if is_sym_char(c) {
-                    value = Sym(str_range(source, start, start + length + 1));
-                } else {
-                    value = Error(Unexpected(c));
-                }
-            } else if matches!(value, Key(_)) {
-                if is_key_end(c) {
-                    break
-                }
-                length += 1;
-                if is_key_char(c) {
-                    value = Key(str_range(source, start, start + length + 1));
-                } else {
-                    value = Error(Unexpected(c));
-                }
-            } else if let Exp(depth, exp) = value {
-                if depth == 0 {
-                    value = Exp(0, str_range(source, start, start + length));
-                    break
-                }
-                length += 1;
-                value = Exp(
-                    if c == ')' { depth-1 } else if c == '(' { depth+1 } else { depth },
-                    str_range(source, start, start + length)
-                );
-            } else if let Num(m) = value {
-                if is_num_end(c) {
-                    break
-                }
-                length += 1;
-                match to_digit(c) {
-                    Ok(n)  => { value = Num(n+10*m); },
-                    Err(e) => { value = Error(e); }
-                }
-            }
-        } else {
-            break
-        }
-    }
-    return Token { value, source, start, length }
-}
-const fn is_whitespace (c: char) -> bool { matches!(c, ' '|'\n'|'\r'|'\t') }
-const fn is_digit      (c: char) -> bool { matches!(c, '0'..='9') }
-const fn is_num_end    (c: char) -> bool { matches!(c, ' '|'\n'|'\r'|'\t'|')') }
-const fn is_key_start  (c: char) -> bool { matches!(c, '/'|'a'..='z') }
-const fn is_key_char   (c: char) -> bool { matches!(c, 'a'..='z'|'0'..='9'|'-'|'/') }
-const fn is_key_end    (c: char) -> bool { matches!(c, ' '|'\n'|'\r'|'\t'|')') }
-const fn is_sym_start  (c: char) -> bool { matches!(c, ':'|'@') }
-const fn is_sym_char   (c: char) -> bool { matches!(c, 'a'..='z'|'A'..='Z'|'0'..='9'|'-') }
-const fn is_sym_end    (c: char) -> bool { matches!(c, ' '|'\n'|'\r'|'\t'|')') }
-const fn is_str_start  (c: char) -> bool { matches!(c, '"') }
-const fn is_str_end    (c: char) -> bool { matches!(c, '"') }
-const fn is_exp_start  (c: char) -> bool { matches!(c, '(') }
-pub const fn to_number <D: Dsl> (digits: &str) -> Result<usize, DslError> {
-    let mut iter = char_indices(digits);
-    let mut value = 0;
-    while let Some(((_, c), next)) = iter.next() {
-        match to_digit(c) {
-            Ok(digit) => value = 10 * value + digit,
-            Err(e) => return Err(e),
-        }
-        iter = next;
-    }
-    Ok(value)
-}
-pub const fn to_digit (c: char) -> Result<usize, DslError> {
-    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))
-    })
-}
-
-/// `T` + [Dsl] -> `Self`.
-pub trait FromDsl<T>: Sized {
-    fn from_dsl (state: &T, dsl: &impl Dsl) -> Perhaps<Self>;
-    fn from_dsl_or (state: &T, dsl: &impl Dsl, err: Box<dyn Error>) -> Usually<Self> {
-        Self::from_dsl(state, dsl)?.ok_or(err)
-    }
-    fn from_dsl_or_else (state: &T, dsl: &impl Dsl, err: impl Fn()->Box<dyn Error>) -> Usually<Self> {
-        Self::from_dsl(state, dsl)?.ok_or_else(err)
-    }
-}
-
-impl<'s, T: FromDsl<U>, U> DslInto<'s, T> for U {
-    fn dsl_into (&self, dsl: &impl Dsl) -> Perhaps<T> {
-        T::from_dsl(self, dsl)
-    }
-}
-
-/// `self` + [Dsl] -> `T`
-pub trait DslInto<'s, T> {
-    fn dsl_into (&'s self, dsl: &impl Dsl) -> Perhaps<T>;
-    fn dsl_into_or (&'s self, dsl: &impl Dsl, err: Box<dyn Error>) -> Usually<T> {
-        self.dsl_into(dsl)?.ok_or(err)
-    }
-    fn dsl_into_or_else (&'s self, dsl: &impl Dsl, err: impl Fn()->Box<dyn Error>) -> Usually<T> {
-        self.dsl_into(dsl)?.ok_or_else(err)
-    }
-}
-
-/// `self` + `T` + -> [Dsl]
-pub trait IntoDsl<T> {
-    fn into_dsl (&self, state: &T) -> Perhaps<impl Dsl>;
-    fn into_dsl_or (&self, state: &T, err: Box<dyn Error>) -> Usually<impl Dsl> {
-        self.into_dsl(state)?.ok_or(err)
-    }
-    fn into_dsl_or_else (&self, state: &T, err: impl Fn()->Box<dyn Error>) -> Usually<impl Dsl> {
-        self.into_dsl(state)?.ok_or_else(err)
-    }
-}
-
-/// `self` + `T` -> [Dsl]
-pub trait DslFrom<T> {
-    fn dsl_from (&self, dsl: &impl Dsl) -> Perhaps<impl Dsl>;
-    fn dsl_from_or (&self, dsl: &impl Dsl, err: Box<dyn Error>) -> Usually<impl Dsl> {
-        self.dsl_from(dsl)?.ok_or(err)
-    }
-    fn dsl_from_or_else (&self, dsl: &impl Dsl, err: impl Fn()->Box<dyn Error>) -> Usually<impl Dsl> {
-        self.dsl_from(dsl)?.ok_or_else(err)
-    }
+#[derive(Error, Debug, Copy, Clone, PartialEq, PanicFmt)]
+pub enum DslError {
+    #[error("parse failed: not implemented")] Unimplemented,
+    #[error("parse failed: empty")] Empty,
+    #[error("parse failed: incomplete")] Incomplete,
+    #[error("parse failed: unexpected character '{0}'")] Unexpected(char),
+    #[error("parse failed: error #{0}")] Code(u8),
+    #[error("end reached")] End
 }
diff --git a/dsl/src/dsl_conv.rs b/dsl/src/dsl_conv.rs
new file mode 100644
index 0000000..65f05d6
--- /dev/null
+++ b/dsl/src/dsl_conv.rs
@@ -0,0 +1,51 @@
+use crate::*;
+
+/// `T` + [Dsl] -> `Self`.
+pub trait FromDsl<T>: Sized {
+    fn from_dsl (state: &T, dsl: &impl Dsl) -> Perhaps<Self>;
+    fn from_dsl_or (state: &T, dsl: &impl Dsl, err: Box<dyn Error>) -> Usually<Self> {
+        Self::from_dsl(state, dsl)?.ok_or(err)
+    }
+    fn from_dsl_or_else (state: &T, dsl: &impl Dsl, err: impl Fn()->Box<dyn Error>) -> Usually<Self> {
+        Self::from_dsl(state, dsl)?.ok_or_else(err)
+    }
+}
+
+impl<'s, T: FromDsl<U>, U> DslInto<'s, T> for U {
+    fn dsl_into (&self, dsl: &impl Dsl) -> Perhaps<T> {
+        T::from_dsl(self, dsl)
+    }
+}
+
+/// `self` + [Dsl] -> `T`
+pub trait DslInto<'s, T> {
+    fn dsl_into (&'s self, dsl: &impl Dsl) -> Perhaps<T>;
+    fn dsl_into_or (&'s self, dsl: &impl Dsl, err: Box<dyn Error>) -> Usually<T> {
+        self.dsl_into(dsl)?.ok_or(err)
+    }
+    fn dsl_into_or_else (&'s self, dsl: &impl Dsl, err: impl Fn()->Box<dyn Error>) -> Usually<T> {
+        self.dsl_into(dsl)?.ok_or_else(err)
+    }
+}
+
+/// `self` + `T` + -> [Dsl]
+pub trait IntoDsl<T> {
+    fn into_dsl (&self, state: &T) -> Perhaps<impl Dsl>;
+    fn into_dsl_or (&self, state: &T, err: Box<dyn Error>) -> Usually<impl Dsl> {
+        self.into_dsl(state)?.ok_or(err)
+    }
+    fn into_dsl_or_else (&self, state: &T, err: impl Fn()->Box<dyn Error>) -> Usually<impl Dsl> {
+        self.into_dsl(state)?.ok_or_else(err)
+    }
+}
+
+/// `self` + `T` -> [Dsl]
+pub trait DslFrom<T> {
+    fn dsl_from (&self, dsl: &impl Dsl) -> Perhaps<impl Dsl>;
+    fn dsl_from_or (&self, dsl: &impl Dsl, err: Box<dyn Error>) -> Usually<impl Dsl> {
+        self.dsl_from(dsl)?.ok_or(err)
+    }
+    fn dsl_from_or_else (&self, dsl: &impl Dsl, err: impl Fn()->Box<dyn Error>) -> Usually<impl Dsl> {
+        self.dsl_from(dsl)?.ok_or_else(err)
+    }
+}
diff --git a/dsl/src/dsl_types.rs b/dsl/src/dsl_types.rs
new file mode 100644
index 0000000..0a5402d
--- /dev/null
+++ b/dsl/src/dsl_types.rs
@@ -0,0 +1,176 @@
+use crate::*;
+
+macro_rules! iter_chars(($source:expr => |$i:ident, $c:ident|$val:expr)=>{
+    while let Some((($i, $c), next)) = char_indices($source).next() {
+        $source = next.as_str(); $val } });
+
+macro_rules! def_peek_seek(($peek:ident, $seek:ident, $seek_start:ident, $seek_length:ident)=>{
+    /// Find a slice corrensponding to a syntax token.
+    const fn $peek (source: &str) -> DslPerhaps<&str> {
+        match $seek(source) {
+            Ok(Some((start, length))) => Ok(Some(str_range(source, start, start + length))),
+            Ok(None) => Ok(None),
+            Err(e) => Err(e) } }
+    /// Find a start and length corresponding to a syntax token.
+    const fn $seek (source: &str) -> DslPerhaps<(usize, usize)> {
+        match $seek_start(source) {
+            Ok(Some(start)) => match $seek_length(str_range(source, start, source.len() - start)) {
+                Ok(Some(length)) => Ok(Some((start, length))),
+                Ok(None) => Ok(None),
+                Err(e) => Err(e),
+            },
+            Ok(None) => Ok(None),
+            Err(e) => Err(e) } } });
+
+const fn is_whitespace (c: char) -> bool { matches!(c, ' '|'\n'|'\r'|'\t') }
+
+pub trait DslExp: Dsl {
+    fn exp (&self) -> DslPerhaps<impl DslExp> {
+        todo!();
+        Ok(Some(self))
+    }
+    fn exp_head (&self) -> DslPerhaps<impl Dsl> {
+        todo!();
+        Ok(Some(self))
+    }
+    fn exp_tail (&self) -> DslPerhaps<impl DslExp> {
+        todo!();
+        Ok(Some(self))
+    }
+    fn exp_next (&mut self) -> DslPerhaps<impl Dsl> {
+        todo!();
+        Ok(Some(self))
+    }
+}
+impl<D: Dsl> DslExp for D {}
+def_peek_seek!(exp_peek, exp_seek, exp_seek_start, exp_seek_length);
+const fn is_exp_start (c: char) -> bool { matches!(c, '(') }
+const fn is_exp_end (c: char) -> bool { matches!(c, ')') }
+const fn exp_seek_start (mut source: &str) -> DslPerhaps<usize> {
+    iter_chars!(source => |i, c| if is_exp_start(c) {
+        return Ok(Some(i))
+    } else if !is_whitespace(c) {
+        return Err(Unexpected(c))
+    });
+    Ok(None)
+}
+const fn exp_seek_length (mut source: &str) -> DslPerhaps<usize> {
+    let mut depth = 0;
+    iter_chars!(source => |i, c| if is_exp_start(c) {
+        depth += 1;
+    } else if is_exp_end(c) {
+        if depth == 0 {
+            return Err(Unexpected(c))
+        } else if depth == 1 {
+            return Ok(Some(i))
+        } else {
+            depth -= 1;
+        }
+    });
+    Ok(None)
+}
+
+pub trait DslSym: Dsl { fn sym (&self) -> DslPerhaps<&str> { sym_peek(self.src()) } }
+impl<D: Dsl> DslSym for D {}
+def_peek_seek!(sym_peek,  sym_seek,  sym_seek_start,  sym_seek_length);
+const fn is_sym_start (c: char) -> bool { matches!(c, ':'|'@') }
+const fn is_sym_char (c: char) -> bool { matches!(c, 'a'..='z'|'A'..='Z'|'0'..='9'|'-') }
+const fn is_sym_end (c: char) -> bool { matches!(c, ' '|'\n'|'\r'|'\t'|')') }
+const fn sym_seek_start (mut source: &str) -> DslPerhaps<usize> {
+    iter_chars!(source => |i, c| if is_sym_start(c) {
+        return Ok(Some(i))
+    } else if !is_whitespace(c) {
+        return Err(Unexpected(c))
+    });
+    Ok(None)
+}
+const fn sym_seek_length (mut source: &str) -> DslPerhaps<usize> {
+    iter_chars!(source => |i, c| if is_sym_end(c) {
+        return Ok(Some(i))
+    } else if !is_sym_char(c) {
+        return Err(Unexpected(c))
+    });
+    Ok(None)
+}
+
+pub trait DslKey: Dsl { fn key (&self) -> DslPerhaps<&str> { key_peek(self.src()) } }
+impl<D: Dsl> DslKey for D {}
+def_peek_seek!(key_peek,  key_seek,  key_seek_start,  key_seek_length);
+const fn is_key_start (c: char) -> bool { matches!(c, '/'|'a'..='z') }
+const fn is_key_char (c: char) -> bool { matches!(c, 'a'..='z'|'0'..='9'|'-'|'/') }
+const fn is_key_end (c: char) -> bool { matches!(c, ' '|'\n'|'\r'|'\t'|')') }
+const fn key_seek_start (mut source: &str) -> DslPerhaps<usize> {
+    iter_chars!(source => |i, c| if is_key_start(c) {
+        return Ok(Some(i))
+    } else if !is_whitespace(c) {
+        return Err(Unexpected(c))
+    });
+    Ok(None)
+}
+const fn key_seek_length (mut source: &str) -> DslPerhaps<usize> {
+    iter_chars!(source => |i, c| if is_key_end(c) {
+        return Ok(Some(i))
+    } else if !is_key_char(c) {
+        return Err(Unexpected(c))
+    });
+    Ok(None)
+}
+
+pub trait DslText: Dsl { fn text (&self) -> DslPerhaps<&str> { text_peek(self.src()) } }
+impl<D: Dsl> DslText for D {}
+def_peek_seek!(text_peek, text_seek, text_seek_start, text_seek_length);
+const fn is_text_start (c: char) -> bool { matches!(c, '"') }
+const fn is_text_end (c: char) -> bool { matches!(c, '"') }
+const fn text_seek_start (mut source: &str) -> DslPerhaps<usize> {
+    iter_chars!(source => |i, c| if is_text_start(c) {
+        return Ok(Some(i))
+    } else if !is_whitespace(c) {
+        return Err(Unexpected(c))
+    });
+    Ok(None)
+}
+const fn text_seek_length (mut source: &str) -> DslPerhaps<usize> {
+    iter_chars!(source => |i, c| if is_text_end(c) { return Ok(Some(i)) });
+    Ok(None)
+}
+
+pub trait DslNum: Dsl { fn num (&self) -> DslPerhaps<&str> { num_peek(self.src()) } }
+impl<D: Dsl> DslNum for D {}
+def_peek_seek!(num_peek,  num_seek,  num_seek_start,  num_seek_length);
+const fn num_seek_start (mut source: &str) -> DslPerhaps<usize> {
+    iter_chars!(source => |i, c| if is_digit(c) {
+        return Ok(Some(i));
+    } else if !is_whitespace(c) {
+        return Err(Unexpected(c))
+    });
+    Ok(None)
+}
+const fn num_seek_length (mut source: &str) -> DslPerhaps<usize> {
+    iter_chars!(source => |i, c| if is_num_end(c) {
+        return Ok(Some(i))
+    } else if !is_digit(c) {
+        return Err(Unexpected(c))
+    });
+    Ok(None)
+}
+const fn is_digit (c: char) -> bool { matches!(c, '0'..='9') }
+const fn is_num_end (c: char) -> bool { matches!(c, ' '|'\n'|'\r'|'\t'|')') }
+pub const fn to_number <D: Dsl> (digits: &str) -> Result<usize, DslError> {
+    let mut iter = char_indices(digits);
+    let mut value = 0;
+    while let Some(((_, c), next)) = iter.next() {
+        match to_digit(c) {
+            Ok(digit) => value = 10 * value + digit,
+            Err(e) => return Err(e),
+        }
+        iter = next;
+    }
+    Ok(value)
+}
+pub const fn to_digit (c: char) -> Result<usize, DslError> {
+    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))
+    })
+}
diff --git a/input/src/input_dsl.rs b/input/src/input_dsl.rs
index 9f6d8de..0bec9a8 100644
--- a/input/src/input_dsl.rs
+++ b/input/src/input_dsl.rs
@@ -54,30 +54,20 @@ impl<E: Clone + Ord, C> EventMap<E, C> {
     }
     /// Create event map from string.
     pub fn from_source (source: impl AsRef<str>) -> Usually<Self> where E: From<Arc<str>> {
-        Self::from_dsl(Cst::from(source.as_ref()))
+        Self::from_dsl(source.as_ref())
     }
     /// Create event map from DSL tokenizer.
     pub fn from_dsl (mut dsl: impl Dsl) -> Usually<Self> where E: From<Arc<str>> {
-        use Val::*;
         let mut map: Self = Default::default();
-        loop {
-            match dsl.exp_next().unwrap() {
-                Str(path) => {
-                    map.0.extend(Self::from_path(PathBuf::from(path.as_ref() as &str))?.0)
-                },
-                Exp(_, e) => match e.head() {
-                    Key(k) if k.as_ref() == "if" => {
-                        todo!("conditional binding {:?}", dsl.tail());
-                    },
-                    Sym(s) => {
-                        let key: Arc<str> = s.as_ref().into();
-                        let key: E = key.into();
-                        map.add(key, Binding::from_dsl(e)?);
-                        todo!("binding {s:?} {:?}", dsl.tail());
-                    },
-                    _ => panic!(),
-                },
-                _ => panic!(),
+        while let Some(dsl) = dsl.exp_next()? {
+            if let Some(path) = dsl.text()? {
+                map.0.extend(Self::from_path(PathBuf::from(path.as_ref() as &str))?.0)
+            } else if dsl.exp_head()?.key()? == Some("if") {
+                todo!()
+                //map.add(sym.into(), Binding::from_dsl(dsl.exp_tail())?);
+            } else if let Some(sym) = dsl.exp_head()?.sym()? {
+                todo!()
+                //map.add(sym.into(), Binding::from_dsl(dsl.exp_tail())?);
             }
         }
         Ok(map)
diff --git a/proc/src/proc_command.rs b/proc/src/proc_command.rs
index d0db6e3..48ae0fe 100644
--- a/proc/src/proc_command.rs
+++ b/proc/src/proc_command.rs
@@ -153,7 +153,6 @@ impl ToTokens for CommandDef {
                 fn from_dsl (state: &#state, value: &impl ::tengri::dsl::Dsl)
                     -> Perhaps<Self>
                 {
-                    use ::tengri::dsl::Val::*;
                     todo!()//Ok(match token { #(#matchers)* _ => None })
                 }
             }
diff --git a/proc/src/proc_expose.rs b/proc/src/proc_expose.rs
index cdfb2af..23bf062 100644
--- a/proc/src/proc_expose.rs
+++ b/proc/src/proc_expose.rs
@@ -67,63 +67,104 @@ impl ToTokens for ExposeImpl {
     }
 }
 
+fn is_num (t: &impl AsRef<str>) -> bool {
+    return matches!(t.as_ref(),
+        | "u8" | "u16" | "u32" | "u64" | "usize"
+        | "i8" | "i16" | "i32" | "i64" | "isize") }
+
 impl ExposeImpl {
     fn expose_variants (
         &self, out: &mut TokenStream2, t: &ExposeType, variants: &BTreeMap<String, Ident>
     ) {
         let Self(ItemImpl { self_ty: state, .. }, ..) = self;
-        let arms = variants.iter().map(|(key, value)|{
+        let type_is = format!("{}", quote! { #t });
+        let variants = variants.iter().map(|(key, value)|{
             let key = LitStr::new(&key, Span::call_site());
-            quote! { #key => state.#value(), }
+            quote! { Some(#key) => Ok(Some(state.#value())), }
         });
-        let arms = Self::with_predefined(t, quote! { #(#arms)* });
-        write_quote_to(out, quote! {
-            /// Generated by [tengri_proc::expose].
-            impl ::tengri::dsl::FromDsl<#state> for #t {
-                fn from_dsl (state: &#state, dsl: &impl Dsl) -> Perhaps<Self> {
-                    Ok(Some(match dsl.val() {
-                        #arms
-                        _ => { return Ok(None) }
-                    }))
+        write_quote_to(out, if &type_is == "bool" {
+            quote! {
+                /// Generated by [tengri_proc::expose].
+                impl ::tengri::dsl::FromDsl<#state> for #t {
+                    fn from_dsl (state: &#state, dsl: &impl Dsl) -> Perhaps<Self> {
+                        match dsl.key()? {
+                            Some("true")  => Ok(Some(true)),
+                            Some("false") => Ok(Some(false)),
+                            _ => match dsl.sym()? { #(#variants)* _ => Ok(None) }
+                        }
+                    }
                 }
             }
-        });
-    }
-    fn with_predefined (t: &ExposeType, variants: impl ToTokens) -> impl ToTokens {
-        let formatted_type = format!("{}", quote! { #t });
-        if &formatted_type == "bool" {
-            return quote! {
-                ::tengri::dsl::Val::Sym(s) => match s.as_ref() {
-                    ":true"  => true,
-                    ":false" => false,
-                    #variants
-                    _ => { return Ok(None) }
-                },
+        } else if is_num(&type_is) {
+            quote! {
+                /// Generated by [tengri_proc::expose].
+                impl ::tengri::dsl::FromDsl<#state> for #t {
+                    fn from_dsl (state: &#state, dsl: &impl Dsl) -> Perhaps<Self> {
+                        match dsl.num()? {
+                            Some(n) => Ok(Some(n.parse::<#t>()?)),
+                            _ => match dsl.sym()? { #(#variants)* _ => Ok(None) }
+                        }
+                    }
+                }
             }
-        }
-        if matches!(formatted_type.as_str(),
-            "u8" | "u16" | "u32" | "u64" | "usize" |
-            "i8" | "i16" | "i32" | "i64" | "isize")
-        {
-            let num_err = LitStr::new(
-                &format!("{{n}}: failed to convert to {formatted_type}"),
-                Span::call_site()
-            );
-            return quote! {
-                ::tengri::dsl::Val::Num(n) => TryInto::<#t>::try_into(n)
-                    .unwrap_or_else(|_|panic!(#num_err)),
-                ::tengri::dsl::Val::Sym(s) => match s.as_ref() {
-                    #variants
-                    _ => { return Ok(None) }
-                },
+        } else {
+            quote! {
+                /// Generated by [tengri_proc::expose].
+                impl ::tengri::dsl::FromDsl<#state> for #t {
+                    fn from_dsl (state: &#state, dsl: &impl Dsl) -> Perhaps<Self> {
+                        match dsl.sym()? { #(#variants)* _ => Ok(None) }
+                    }
+                }
             }
-        }
-        return quote! {
-            ::tengri::dsl::Val::Sym(s) => match s.as_ref() {
-                #variants
-                _ => { return Ok(None) }
-            },
-        }
+        })
+        //let arms = variants.iter().map(|(key, value)|{
+            //let key = LitStr::new(&key, Span::call_site());
+            //quote! { #key => state.#value(), }
+        //});
+        //if &type_is == "bool" {
+            //return quote! {
+                //::tengri::dsl::Val::Sym(s) => match s.as_ref() {
+                    //":true"  => true,
+                    //":false" => false,
+                    //#variants
+                    //_ => { return Ok(None) }
+                //},
+            //}
+        //}
+        //if matches!(type_is.as_str(),
+            //"u8" | "u16" | "u32" | "u64" | "usize" |
+            //"i8" | "i16" | "i32" | "i64" | "isize")
+        //{
+            //let num_err = LitStr::new(
+                //&format!("{{n}}: failed to convert to {type_is}"),
+                //Span::call_site()
+            //);
+            //return quote! {
+                //::tengri::dsl::Val::Num(n) => TryInto::<#t>::try_into(n)
+                    //.unwrap_or_else(|_|panic!(#num_err)),
+                //::tengri::dsl::Val::Sym(s) => match s.as_ref() {
+                    //#variants
+                    //_ => { return Ok(None) }
+                //},
+            //}
+        //}
+        //let arms = quote! {
+            //::tengri::dsl::Val::Sym(s) => match s.as_ref() {
+                //#variants
+                //_ => { return Ok(None) }
+            //},
+        //};
+        //let builtins =
+        //write_quote_to(out, quote! {
+            ///// Generated by [tengri_proc::expose].
+            //impl ::tengri::dsl::FromDsl<#state> for #t {
+                //fn from_dsl (state: &#state, dsl: &impl Dsl) -> Perhaps<Self> {
+                    //$builtins
+                    //$defined
+                    //Ok(None)
+                //}
+            //}
+        //});
     }
 }