dsl gets the gordian treatment

dsl/src/dsl_ast.rs

@@ -1,70 +1,36 @@
 use crate::*;
 use std::sync::Arc;
-use std::fmt::{Debug, Display, Formatter};
+use std::borrow::Cow;
 
-#[derive(Clone, Default, Debug)]
-pub enum Ast {
-    #[default] Nil,
-    Err(DslError),
-    Num(usize),
-    Sym(Arc<str>),
-    Key(Arc<str>),
-    Str(Arc<str>),
-    Exp(Arc<Box<dyn AstIter>>),
-}
+/// Owns its values, and has no metadata.
+pub type AstToken = Token<AstValue, AstMeta>;
 
-/// Emits tokens.
-pub trait AstIter: Debug {
-    fn peek (&self) -> Option<Ast>;
-    fn next (&mut self) -> Option<Ast>;
-    fn rest (self) -> Option<Box<dyn AstIter>>;
-}
+#[derive(Debug, Copy, Clone, Default, PartialEq)]
+pub struct AstMeta;
 
-/// A [Cst] can be used as an [Ast].
-impl<'source: 'static> AstIter for Cst<'source> {
-    fn peek (&self) -> Option<Ast> {
-        Cst::peek(self).map(|token|token.value.into())
-    }
-    fn next (&mut self) -> Option<Ast> {
-        Iterator::next(self).map(|token|token.value.into())
-    }
-    fn rest (self) -> Option<Box<dyn AstIter>> {
-        self.peek().is_some().then(||Box::new(self) as Box<dyn AstIter>)
-    }
-}
-
-impl std::fmt::Display for Ast {
-    fn fmt (&self, out: &mut Formatter) -> Result<(), std::fmt::Error> {
-        use Ast::*;
-        write!(out, "{}", match self {
-            Nil => String::new(),
-            Err(e) => format!("[error: {e}]"),
-            Num(n) => format!("{n}"),
-            Sym(s) => format!("{s}"),
-            Key(s) => format!("{s}"),
-            Str(s) => format!("{s}"),
-            Exp(e) => format!("{e:?}"),
-        })
-    }
-}
-
-impl<'source: 'static> From<CstValue<'source>> for Ast {
-    fn from (other: CstValue<'source>) -> Self {
-        use CstValue::*;
-        match other {
-            Nil => Self::Nil,
-            Err(e) => Self::Err(e),
-            Num(u) => Self::Num(u),
-            Sym(s) => Self::Sym(s.into()),
-            Key(s) => Self::Key(s.into()),
-            Str(s) => Self::Str(s.into()),
-            Exp(_, s) => Self::Exp(Arc::new(s.into())),
+pub type AstValue = Value<Arc<str>, AstExp>;
+impl<'source> From<CstValue<'source>> for AstValue {
+    fn from (value: CstValue<'source>) -> Self {
+        use Value::*;
+        match value {
+            Nil    => Nil,
+            Err(e) => Err(e),
+            Num(u) => Num(u),
+            Sym(s) => Sym(s.into()),
+            Key(s) => Key(s.into()),
+            Str(s) => Str(s.into()),
+            Exp(x) => Exp(x.into()),
         }
     }
 }
 
-impl<'source: 'static> Into<Box<dyn AstIter>> for Cst<'source> {
-    fn into (self) -> Box<dyn AstIter> {
-        Box::new(self)
+#[derive(Clone, Default, PartialEq)]
+pub struct AstExp(pub Vec<AstToken>);
+impl<'source> From<CstExp<'source>> for AstExp {
+    fn from (exp: CstExp<'source>) -> AstExp {
+        AstExp(exp.words.map(|token|Token(
+            AstValue::from(token.value()),
+            AstMeta,
+        )).collect())
     }
 }

dsl/src/dsl_cst.rs

@@ -1,291 +1,17 @@
 use crate::*;
 
-/// Provides a native [Iterator] API over [CstConstIter],
-/// emitting [CstToken] items.
-///
-/// [Cst::next] returns just the [CstToken] and mutates `self`,
-/// instead of returning an updated version of the struct as [CstConstIter::next] does.
-#[derive(Copy, Clone, Debug, Default, PartialEq)]
-pub struct Cst<'a>(pub CstConstIter<'a>);
+/// Keeps the reference to the source slice.
+pub type CstToken<'source> = Token<CstValue<'source>, CstMeta<'source>>;
 
-/// Owns a reference to the source text.
-/// [CstConstIter::next] emits subsequent pairs of:
-///   * a [CstToken] 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<'a>(pub &'a str);
-
-/// A CST token, with reference to the source slice.
-#[derive(Debug, Copy, Clone, Default, PartialEq)] pub struct CstToken<'source> {
+#[derive(Debug, Copy, Clone, Default, PartialEq)] pub struct CstMeta<'source> {
     pub source: &'source str,
     pub start:  usize,
     pub length: usize,
-    pub value:  CstValue<'source>,
 }
 
-/// The meaning of a CST token. Strip the source from this to get an [AstValue].
-#[derive(Debug, Copy, Clone, Default, PartialEq)] pub enum CstValue<'source> {
-    #[default] Nil,
-    Err(DslError),
-    Num(usize),
-    Sym(&'source str),
-    Key(&'source str),
-    Str(&'source str),
-    Exp(usize, Cst<'source>),
-}
+pub type CstValue<'source> = Value<&'source str, CstExp<'source>>;
 
-impl<'a> Cst<'a> {
-    pub const fn new (source: &'a str) -> Self {
-        Self(CstConstIter::new(source))
-    }
-    pub const fn peek (&self) -> Option<CstToken<'a>> {
-        self.0.peek()
-    }
-}
-
-impl<'a> Iterator for Cst<'a> {
-    type Item = CstToken<'a>;
-    fn next (&mut self) -> Option<CstToken<'a>> {
-        self.0.next().map(|(item, rest)|{self.0 = rest; item})
-    }
-}
-
-impl<'a> From<&'a str> for Cst<'a> {
-    fn from (source: &'a str) -> Self{
-        Self(CstConstIter(source))
-    }
-}
-
-impl<'a> From<CstConstIter<'a>> for Cst<'a> {
-    fn from (source: CstConstIter<'a>) -> Self{
-        Self(source)
-    }
-}
-
-/// 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 = $Item;
-            type IntoIter = Self;
-        }
-    }
-}
-
-const_iter!(<'a>|self: CstConstIter<'a>| => CstToken<'a> => self.next_mut().map(|(result, _)|result));
-
-impl<'a> From<&'a str> for CstConstIter<'a> {
-    fn from (source: &'a str) -> Self{
-        Self::new(source)
-    }
-}
-
-impl<'a> CstConstIter<'a> {
-    pub const fn new (source: &'a str) -> Self {
-        Self(source)
-    }
-    pub const fn chomp (&self, index: usize) -> Self {
-        Self(split_at(self.0, index).1)
-    }
-    pub const fn next (mut self) -> Option<(CstToken<'a>, Self)> {
-        Self::next_mut(&mut self)
-    }
-    pub const fn peek (&self) -> Option<CstToken<'a>> {
-        peek_src(self.0)
-    }
-    pub const fn next_mut (&mut self) -> Option<(CstToken<'a>, Self)> {
-        match self.peek() {
-            Some(token) => Some((token, self.chomp(token.end()))),
-            None => None
-        }
-    }
-}
-
-/// Static iteration helper.
-#[macro_export] macro_rules! iterate {
-    ($expr:expr => $arg: pat => $body:expr) => {
-        let mut iter = $expr;
-        while let Some(($arg, next)) = iter.next() {
-            $body;
-            iter = next;
-        }
-    }
-}
-
-pub const fn peek_src <'a> (source: &'a str) -> Option<CstToken<'a>> {
-    use CstValue::*;
-    let mut token: CstToken<'a> = CstToken::new(source, 0, 0, Nil);
-    iterate!(char_indices(source) => (start, c) => token = match token.value() {
-        Err(_) => return Some(token),
-        Nil => match c {
-            ' '|'\n'|'\r'|'\t' =>
-                token.grow(),
-            '(' =>
-                CstToken::new(source, start, 1, Exp(1, Cst::new(str_range(source, start, start + 1)))),
-            '"' =>
-                CstToken::new(source, start, 1, Str(str_range(source, start, start + 1))),
-            ':'|'@' =>
-                CstToken::new(source, start, 1, Sym(str_range(source, start, start + 1))),
-            '/'|'a'..='z' =>
-                CstToken::new(source, start, 1, Key(str_range(source, start, start + 1))),
-            '0'..='9' =>
-                CstToken::new(source, start, 1, match to_digit(c) {
-                    Ok(c) => CstValue::Num(c),
-                    Result::Err(e) => CstValue::Err(e)
-                }),
-            _ => token.error(Unexpected(c))
-        },
-        Str(_) => match c {
-            '"' => return Some(token),
-            _ => token.grow_str(),
-        },
-        Num(n) => match c {
-            '0'..='9' => token.grow_num(n, c),
-            ' '|'\n'|'\r'|'\t'|')' => return Some(token),
-            _ => token.error(Unexpected(c))
-        },
-        Sym(_) => match c {
-            'a'..='z'|'A'..='Z'|'0'..='9'|'-' => token.grow_sym(),
-            ' '|'\n'|'\r'|'\t'|')' => return Some(token),
-            _ => token.error(Unexpected(c))
-        },
-        Key(_) => match c {
-            'a'..='z'|'0'..='9'|'-'|'/' => token.grow_key(),
-            ' '|'\n'|'\r'|'\t'|')' => return Some(token),
-            _ => token.error(Unexpected(c))
-        },
-        Exp(depth, _) => match depth {
-            0 => return Some(token.grow_exp()),
-            _ => match c {
-                ')' => token.grow_out(),
-                '(' => token.grow_in(),
-                 _  => token.grow_exp(),
-            }
-        },
-    });
-    match token.value() {
-        Nil => None,
-        _ => Some(token),
-    }
-}
-
-pub const fn to_number (digits: &str) -> DslResult<usize> {
-    let mut value = 0;
-    iterate!(char_indices(digits) => (_, c) => match to_digit(c) {
-        Ok(digit) => value = 10 * value + digit,
-        Result::Err(e) => return Result::Err(e)
-    });
-    Ok(value)
-}
-
-pub const fn to_digit (c: char) -> DslResult<usize> {
-    Ok(match c {
-        '0' => 0, '1' => 1, '2' => 2, '3' => 3, '4' => 4,
-        '5' => 5, '6' => 6, '7' => 7, '8' => 8, '9' => 9,
-        _ => return Result::Err(Unexpected(c))
-    })
-}
-
-impl<'source> CstToken<'source> {
-    pub const fn new (
-        source: &'source str, start: usize, length: usize, value: CstValue<'source>
-    ) -> Self {
-        Self { source, start, length, value }
-    }
-    pub const fn end (&self) -> usize {
-        self.start.saturating_add(self.length)
-    }
-    pub const fn slice (&'source self) -> &'source str {
-        self.slice_source(self.source)
-    }
-    pub const fn slice_source <'range> (&'source self, source: &'range str) -> &'range str {
-        str_range(source, self.start, self.end())
-    }
-    pub const fn slice_source_exp <'range> (&'source self, source: &'range str) -> &'range str {
-        str_range(source, self.start.saturating_add(1), self.end())
-    }
-    pub const fn with_value (self, value: CstValue<'source>) -> Self {
-        Self { value, ..self }
-    }
-    pub const fn value (&self) -> CstValue {
-        self.value
-    }
-    pub const fn error (self, error: DslError) -> Self {
-        Self { value: CstValue::Err(error), ..self }
-    }
-    pub const fn grow (self) -> Self {
-        Self { length: self.length.saturating_add(1), ..self }
-    }
-    pub const fn grow_num (self, m: usize, c: char) -> Self {
-        use CstValue::*;
-        match to_digit(c) {
-            Ok(n) => Self { value: Num(10*m+n), ..self.grow() },
-            Result::Err(e) => Self { value: Err(e), ..self.grow() },
-        }
-    }
-    pub const fn grow_key (self) -> Self {
-        use CstValue::*;
-        let token = self.grow();
-        token.with_value(Key(token.slice_source(self.source)))
-    }
-    pub const fn grow_sym (self) -> Self {
-        use CstValue::*;
-        let token = self.grow();
-        token.with_value(Sym(token.slice_source(self.source)))
-    }
-    pub const fn grow_str (self) -> Self {
-        use CstValue::*;
-        let token = self.grow();
-        token.with_value(Str(token.slice_source(self.source)))
-    }
-    pub const fn grow_exp (self) -> Self {
-        use CstValue::*;
-        let token = self.grow();
-        if let Exp(depth, _) = token.value {
-            token.with_value(Exp(depth, Cst::new(token.slice_source_exp(self.source))))
-        } else {
-            unreachable!()
-        }
-    }
-    pub const fn grow_in (self) -> Self {
-        let token = self.grow_exp();
-        if let CstValue::Exp(depth, source) = token.value {
-            token.with_value(CstValue::Exp(depth.saturating_add(1), source))
-        } else {
-            unreachable!()
-        }
-    }
-    pub const fn grow_out (self) -> Self {
-        let token = self.grow_exp();
-        if let CstValue::Exp(depth, source) = token.value {
-            if depth > 0 {
-                token.with_value(CstValue::Exp(depth - 1, source))
-            } else {
-                return self.error(Unexpected(')'))
-            }
-        } else {
-            unreachable!()
-        }
-    }
-}
-
-impl<'source> std::fmt::Display for CstValue<'source> {
-    fn fmt (&self, out: &mut std::fmt::Formatter) -> Result<(), std::fmt::Error> {
-        use CstValue::*;
-        write!(out, "{}", match self {
-            Nil    => String::new(),
-            Err(e) => format!("[error: {e}]"),
-            Num(n) => format!("{n}"),
-            Sym(s) => format!("{s}"),
-            Key(s) => format!("{s}"),
-            Str(s) => format!("{s}"),
-            Exp(_, e) => format!("{e:?}"),
-        })
-    }
+#[derive(Debug, Copy, Clone, Default, PartialEq)] pub struct CstExp<'source> {
+    pub depth: usize,
+    pub words: SourceIter<'source>
 }

dsl/src/dsl_display.rs

@@ -0,0 +1,39 @@
+use crate::*;
+
+use std::fmt::{Debug, Display, Formatter, Error as FormatError};
+
+impl Display for AstValue {
+    fn fmt (&self, out: &mut Formatter) -> Result<(), FormatError> {
+        use Value::*;
+        write!(out, "{}", match self {
+            Nil => String::new(),
+            Err(e) => format!("[error: {e}]"),
+            Num(n) => format!("{n}"),
+            Sym(s) => format!("{s}"),
+            Key(s) => format!("{s}"),
+            Str(s) => format!("{s}"),
+            Exp(e) => format!("{e:?}"),
+        })
+    }
+}
+
+impl Debug for AstExp {
+    fn fmt (&self, out: &mut Formatter) -> Result<(), FormatError> {
+        todo!()
+    }
+}
+
+impl<'source> Display for CstValue<'source> {
+    fn fmt (&self, out: &mut Formatter) -> Result<(), FormatError> {
+        use Value::*;
+        write!(out, "{}", match self {
+            Nil    => String::new(),
+            Err(e) => format!("[error: {e}]"),
+            Num(n) => format!("{n}"),
+            Sym(s) => format!("{s}"),
+            Key(s) => format!("{s}"),
+            Str(s) => format!("{s}"),
+            Exp(e) => format!("{e:?}"),
+        })
+    }
+}

dsl/src/dsl_domain.rs

@@ -13,13 +13,25 @@ pub trait Eval<Input, Output> {
     }
 }
 
+//impl<S: Eval<I, O>, I, O> Eval<I, O> for &S {
+    //fn try_eval (&self, input: I) -> Perhaps<O> {
+        //(*self).try_eval(input)
+    //}
+//}
+
+//impl<S: Eval<I, O>, I: Ast, O: Dsl<S>> Eval<I, O> for S {
+    //fn try_eval (&self, input: I) -> Perhaps<O> {
+        //Dsl::try_provide(self, input)
+    //}
+//}
+
 /// May construct [Self] from token stream.
 pub trait Dsl<State>: Sized {
-    fn try_provide (state: State, source: Ast) -> Perhaps<Self>;
+    fn try_provide (state: &State, source: impl DslValue) -> Perhaps<Self>;
     fn provide <E: Into<Box<dyn std::error::Error>>, F: Fn()->E> (
-        state: State, source: Ast, error: F
+        state: &State, source: impl DslValue, error: F
     ) -> Usually<Self> {
-        let next = source.clone();
+        let next = format!("{source:?}");
         if let Some(value) = Self::try_provide(state, source)? {
             Ok(value)
         } else {
@@ -28,10 +40,6 @@ pub trait Dsl<State>: Sized {
     }
 }
 
-impl<T: Dsl<S>, S> Eval<Ast, T> for S {
-    fn try_eval (&self, input: Ast) -> Perhaps<T> { todo!() }
-}
-
 //pub trait Give<'state, 'source, Type> {
     ///// Implement this to be able to [Give] [Type] from the [Cst].
     ///// Advance the stream if returning `Ok<Some<Type>>`.

dsl/src/dsl_iter.rs

@@ -0,0 +1,96 @@
+use crate::*;
+
+pub trait DslIter {
+    type Token: DslToken;
+    fn peek (&self) -> Option<<Self::Token as DslToken>::Value>;
+    fn next (&mut self) -> Option<<Self::Token as DslToken>::Value>;
+    fn rest (&self) -> Option<&[<Self::Token as DslToken>::Value]>;
+}
+
+/// Provides a native [Iterator] API over [SourceConstIter],
+/// emitting [CstToken] items.
+///
+/// [Cst::next] returns just the [CstToken] and mutates `self`,
+/// instead of returning an updated version of the struct as [SourceConstIter::next] does.
+#[derive(Copy, Clone, Debug, Default, PartialEq)]
+pub struct SourceIter<'a>(pub SourceConstIter<'a>);
+
+impl<'a> SourceIter<'a> {
+    pub const fn new (source: &'a str) -> Self {
+        Self(SourceConstIter::new(source))
+    }
+    pub const fn peek (&self) -> Option<CstToken<'a>> {
+        self.0.peek()
+    }
+}
+
+impl<'a> Iterator for SourceIter<'a> {
+    type Item = CstToken<'a>;
+    fn next (&mut self) -> Option<CstToken<'a>> {
+        self.0.next().map(|(item, rest)|{self.0 = rest; item})
+    }
+}
+
+impl<'a> From<&'a str> for SourceIter<'a> {
+    fn from (source: &'a str) -> Self{
+        Self(SourceConstIter(source))
+    }
+}
+
+/// 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;
+        }
+    }
+}
+
+/// Owns a reference to the source text.
+/// [SourceConstIter::next] emits subsequent pairs of:
+///   * a [CstToken] and
+///   * the source text remaining
+///     * [ ] TODO: maybe [SourceConstIter::next] should wrap the remaining source in `Self` ?
+#[derive(Copy, Clone, Debug, Default, PartialEq)]
+pub struct SourceConstIter<'a>(pub &'a str);
+
+impl<'a> From<SourceConstIter<'a>> for SourceIter<'a> {
+    fn from (source: SourceConstIter<'a>) -> Self{
+        Self(source)
+    }
+}
+
+impl<'a> From<&'a str> for SourceConstIter<'a> {
+    fn from (source: &'a str) -> Self{
+        Self::new(source)
+    }
+}
+
+impl<'a> SourceConstIter<'a> {
+    pub const fn new (source: &'a str) -> Self {
+        Self(source)
+    }
+    pub const fn chomp (&self, index: usize) -> Self {
+        Self(split_at(self.0, index).1)
+    }
+    pub const fn next (mut self) -> Option<(CstToken<'a>, Self)> {
+        Self::next_mut(&mut self)
+    }
+    pub const fn peek (&self) -> Option<CstToken<'a>> {
+        peek_src(self.0)
+    }
+    pub const fn next_mut (&mut self) -> Option<(CstToken<'a>, Self)> {
+        match self.peek() {
+            Some(token) => Some((token, self.chomp(token.end()))),
+            None => None
+        }
+    }
+}
+
+const_iter!(<'a>|self: SourceConstIter<'a>| => CstToken<'a> => self.next_mut().map(|(result, _)|result));

dsl/src/dsl_token.rs

@@ -0,0 +1,264 @@
+use crate::*;
+
+#[derive(PartialEq, Clone, Default, Debug)]
+pub enum Value<
+    S: PartialEq + Clone + Default + Debug,
+    X: PartialEq + Clone + Default + Debug,
+> {
+    #[default] Nil, Err(DslError), Num(usize), Sym(S), Key(S), Str(S), Exp(X),
+}
+
+pub trait DslValue: PartialEq + Clone + Default + Debug {
+    type Err: PartialEq + Clone + Debug;
+    type Num: PartialEq + Copy + Clone + Default + Debug;
+    type Str: PartialEq + Clone + Default + Debug;
+    type Exp: PartialEq + Clone + Default + Debug;
+    fn nil (&self) -> bool;
+    fn err (&self) -> Option<&Self::Err>;
+    fn num (&self) -> Option<Self::Num>;
+    fn sym (&self) -> Option<&Self::Str>;
+    fn key (&self) -> Option<&Self::Str>;
+    fn str (&self) -> Option<&Self::Str>;
+    fn exp (&self) -> Option<&Self::Exp>;
+    fn exp_head (&self) -> Option<&Self>   { None } // TODO
+    fn exp_tail (&self) -> Option<&[Self]> { None } // TODO
+}
+
+impl<
+    Str: PartialEq + Clone + Default + Debug,
+    Exp: PartialEq + Clone + Default + Debug,
+> DslValue for Value<Str, Exp> {
+    type Err = DslError;
+    type Num = usize;
+    type Str = Str;
+    type Exp = Exp;
+    fn nil (&self) -> bool {
+        matches!(self, Self::Nil)
+    }
+    fn err (&self) -> Option<&DslError> {
+        if let Self::Err(e) = self { Some(e) } else { None }
+    }
+    fn num (&self) -> Option<usize> {
+        if let Self::Num(n) = self { Some(*n) } else { None }
+    }
+    fn sym (&self) -> Option<&Str> {
+        if let Self::Sym(s) = self { Some(s) } else { None }
+    }
+    fn key (&self) -> Option<&Str> {
+        if let Self::Key(k) = self { Some(k) } else { None }
+    }
+    fn str (&self) -> Option<&Str> {
+        if let Self::Str(s) = self { Some(s) } else { None }
+    }
+    fn exp (&self) -> Option<&Exp> {
+        if let Self::Exp(x) = self { Some(x) } else { None }
+    }
+}
+
+
+#[derive(PartialEq, Clone, Default, Debug)]
+pub struct Token<
+    V: PartialEq + Clone + Default + Debug,
+    M: PartialEq + Clone + Default + Debug,
+>(pub V, pub M);
+
+pub trait DslToken: PartialEq + Clone + Default + Debug {
+    type Value: DslValue;
+    type Meta: Clone + Default + Debug;
+    fn value (&self) -> &Self::Value;
+    fn meta (&self) -> &Self::Meta;
+}
+
+impl<V: DslValue, M: PartialEq + Clone + Default + Debug> DslToken for Token<V, M> {
+    type Value = V;
+    type Meta  = M;
+    fn value (&self) -> &Self::Value { 
+        &self.0
+    }
+    fn meta (&self) -> &Self::Meta {
+        &self.1
+    }
+}
+
+impl<'source> CstToken<'source> {
+    pub const fn new (
+        source: &'source str, start: usize, length: usize, value: CstValue<'source>
+    ) -> Self {
+        Self(value, CstMeta { source, start, length })
+    }
+    pub const fn end (&self) -> usize {
+        self.1.start.saturating_add(self.1.length)
+    }
+    pub const fn slice (&'source self) -> &'source str {
+        self.slice_source(self.1.source)
+    }
+    pub const fn slice_source <'range> (&'source self, source: &'range str) -> &'range str {
+        str_range(source, self.1.start, self.end())
+    }
+    pub const fn slice_source_exp <'range> (&'source self, source: &'range str) -> &'range str {
+        str_range(source, self.1.start.saturating_add(1), self.end())
+    }
+    pub const fn with_value (self, value: CstValue<'source>) -> Self {
+        Self(value, self.1)
+    }
+    pub const fn value (&self) -> CstValue<'source> {
+        self.0
+    }
+    pub const fn error (self, error: DslError) -> Self {
+        Self(Value::Err(error), self.1)
+    }
+    pub const fn grow (self) -> Self {
+        Self(self.0, CstMeta { length: self.1.length.saturating_add(1), ..self.1 })
+    }
+    pub const fn grow_num (self, m: usize, c: char) -> Self {
+        use Value::*;
+        match to_digit(c) {
+            Result::Ok(n)  => Self(Num(10*m+n), self.grow().1),
+            Result::Err(e) => Self(Err(e), self.grow().1),
+        }
+    }
+    pub const fn grow_key (self) -> Self {
+        use Value::*;
+        let token = self.grow();
+        token.with_value(Key(token.slice_source(self.1.source)))
+    }
+    pub const fn grow_sym (self) -> Self {
+        use Value::*;
+        let token = self.grow();
+        token.with_value(Sym(token.slice_source(self.1.source)))
+    }
+    pub const fn grow_str (self) -> Self {
+        use Value::*;
+        let token = self.grow();
+        token.with_value(Str(token.slice_source(self.1.source)))
+    }
+    pub const fn grow_exp (self) -> Self {
+        use Value::*;
+        let token = self.grow();
+        if let Exp(depth, _) = token.value() {
+            token.with_value(Exp(depth, Cst::new(token.slice_source_exp(self.source))))
+        } else {
+            unreachable!()
+        }
+    }
+    pub const fn grow_in (self) -> Self {
+        let token = self.grow_exp();
+        if let Value::Exp(depth, source) = token.value {
+            token.with_value(Value::Exp(depth.saturating_add(1), source))
+        } else {
+            unreachable!()
+        }
+    }
+    pub const fn grow_out (self) -> Self {
+        let token = self.grow_exp();
+        if let Value::Exp(depth, source) = token.value {
+            if depth > 0 {
+                token.with_value(Value::Exp(depth - 1, source))
+            } else {
+                return self.error(Unexpected(')'))
+            }
+        } else {
+            unreachable!()
+        }
+    }
+}
+
+pub const fn to_number (digits: &str) -> DslResult<usize> {
+    let mut value = 0;
+    iterate!(char_indices(digits) => (_, c) => match to_digit(c) {
+        Ok(digit) => value = 10 * value + digit,
+        Result::Err(e) => return Result::Err(e)
+    });
+    Ok(value)
+}
+
+pub const fn to_digit (c: char) -> DslResult<usize> {
+    Ok(match c {
+        '0' => 0, '1' => 1, '2' => 2, '3' => 3, '4' => 4,
+        '5' => 5, '6' => 6, '7' => 7, '8' => 8, '9' => 9,
+        _ => return Result::Err(Unexpected(c))
+    })
+}
+
+/// 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;
+        }
+    }
+}
+
+pub const fn peek_src <'a> (source: &'a str) -> Option<CstToken<'a>> {
+    use Value::*;
+    let mut token: CstToken<'a> = CstToken::new(source, 0, 0, Nil);
+    iterate!(char_indices(source) => (start, c) => token = match token.value() {
+        Err(_) => return Some(token),
+        Nil => match c {
+            ' '|'\n'|'\r'|'\t' =>
+                token.grow(),
+            '(' =>
+                CstToken::new(source, start, 1, Exp(1, Cst::new(str_range(source, start, start + 1)))),
+            '"' =>
+                CstToken::new(source, start, 1, Str(str_range(source, start, start + 1))),
+            ':'|'@' =>
+                CstToken::new(source, start, 1, Sym(str_range(source, start, start + 1))),
+            '/'|'a'..='z' =>
+                CstToken::new(source, start, 1, Key(str_range(source, start, start + 1))),
+            '0'..='9' =>
+                CstToken::new(source, start, 1, match to_digit(c) {
+                    Ok(c) => Value::Num(c),
+                    Result::Err(e) => Value::Err(e)
+                }),
+            _ => token.error(Unexpected(c))
+        },
+        Str(_) => match c {
+            '"' => return Some(token),
+            _ => token.grow_str(),
+        },
+        Num(n) => match c {
+            '0'..='9' => token.grow_num(n, c),
+            ' '|'\n'|'\r'|'\t'|')' => return Some(token),
+            _ => token.error(Unexpected(c))
+        },
+        Sym(_) => match c {
+            'a'..='z'|'A'..='Z'|'0'..='9'|'-' => token.grow_sym(),
+            ' '|'\n'|'\r'|'\t'|')' => return Some(token),
+            _ => token.error(Unexpected(c))
+        },
+        Key(_) => match c {
+            'a'..='z'|'0'..='9'|'-'|'/' => token.grow_key(),
+            ' '|'\n'|'\r'|'\t'|')' => return Some(token),
+            _ => token.error(Unexpected(c))
+        },
+        Exp(depth, _) => match depth {
+            0 => return Some(token.grow_exp()),
+            _ => match c {
+                ')' => token.grow_out(),
+                '(' => token.grow_in(),
+                 _  => token.grow_exp(),
+            }
+        },
+    });
+    match token.value() {
+        Nil => None,
+        _ => Some(token),
+    }
+}
+
+//impl<S1, S2: From<S1>, X1, X2: From<S2>> From<Value<S1, X1>> for Value<S2, X2> {
+    //fn from (other: Value<S2, X2>) -> Self {
+        //use Value::*;
+        //match other {
+            //Nil    => Nil,
+            //Err(e) => Err(e),
+            //Num(u) => Num(u),
+            //Sym(s) => Sym(s.into()),
+            //Key(s) => Key(s.into()),
+            //Str(s) => Str(s.into()),
+            //Exp(x) => Exp(x.into()),
+        //}
+    //}
+//}

dsl/src/lib.rs

@@ -46,8 +46,11 @@ pub(crate) use self::DslError::*;
 
 mod dsl_ast;     pub use self::dsl_ast::*;
 mod dsl_cst;     pub use self::dsl_cst::*;
+mod dsl_display; pub use self::dsl_display::*;
 mod dsl_domain;  pub use self::dsl_domain::*;
 mod dsl_error;   pub use self::dsl_error::*;
+mod dsl_iter;    pub use self::dsl_iter::*;
+mod dsl_token;   pub use self::dsl_token::*;
 
 #[cfg(test)] mod test_token_iter {
     use crate::*;