wip: refactor dsl

dsl/src/cst.rs

@@ -0,0 +1,290 @@
+//! 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.
+
+use crate::*;
+
+/// Implement the const iterator pattern.
+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 = $Item;
+            type IntoIter = Self;
+        }
+    }
+}
+
+/// Static iteration helper used by [cst].
+macro_rules! iterate {
+    ($expr:expr => $arg: pat => $body:expr) => {
+        let mut iter = $expr;
+        while let Some(($arg, next)) = iter.next() {
+            $body;
+            iter = next;
+        }
+    }
+}
+
+/// CST stores strings as source references and expressions as [SourceIter] instances.
+pub type CstValue<'source> = DslValue<&'source str, SourceIter<'source>>;
+
+/// Token sharing memory with source reference.
+#[derive(Debug, Copy, Clone, Default, PartialEq)]
+pub struct Cst<'src> {
+    /// Reference to source text.
+    pub source: &'src str,
+    /// Index of 1st character of token.
+    pub start:  usize,
+    /// Length of token.
+    pub length: usize,
+    /// Meaning of token.
+    pub value:  CstValue<'src>,
+}
+
+impl<'src> Cst<'src> {
+    pub const fn new (
+        source: &'src str,
+        start:  usize,
+        length: usize,
+        value:  CstValue<'src>
+    ) -> Self {
+        Self { source, start, length, value }
+    }
+    pub const fn end (&self) -> usize {
+        self.start.saturating_add(self.length)
+    }
+    pub const fn slice (&'src self) -> &'src str {
+        self.slice_source(self.source)
+    }
+    pub const fn slice_source <'range> (&'src self, source: &'range str) -> &'range str {
+        str_range(source, self.start, self.end())
+    }
+    pub const fn slice_source_exp <'range> (&'src self, source: &'range str) -> &'range str {
+        str_range(source, self.start.saturating_add(1), self.end())
+    }
+    pub const fn with_value (self, value: CstValue<'src>) -> Self {
+        Self { value, ..self }
+    }
+    pub const fn value (&self) -> CstValue<'src> {
+        self.value
+    }
+    pub const fn error (self, error: DslError) -> Self {
+        Self { value: DslValue::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 {
+        match to_digit(c) {
+            Result::Ok(n)  => Self { value: DslValue::Num(10*m+n), ..self.grow() },
+            Result::Err(e) => Self { value: DslValue::Err(e),      ..self.grow() },
+        }
+    }
+    pub const fn grow_key (self) -> Self {
+        let token = self.grow();
+        token.with_value(DslValue::Key(token.slice_source(self.source)))
+    }
+    pub const fn grow_sym (self) -> Self {
+        let token = self.grow();
+        token.with_value(DslValue::Sym(token.slice_source(self.source)))
+    }
+    pub const fn grow_str (self) -> Self {
+        let token = self.grow();
+        token.with_value(DslValue::Str(token.slice_source(self.source)))
+    }
+    pub const fn grow_exp (self) -> Self {
+        let token = self.grow();
+        if let DslValue::Exp(depth, _) = token.value() {
+            token.with_value(DslValue::Exp(depth, SourceIter::new(token.slice_source_exp(self.source))))
+        } else {
+            unreachable!()
+        }
+    }
+    pub const fn grow_in (self) -> Self {
+        let token = self.grow_exp();
+        if let DslValue::Exp(depth, source) = token.value() {
+            token.with_value(DslValue::Exp(depth.saturating_add(1), source))
+        } else {
+            unreachable!()
+        }
+    }
+    pub const fn grow_out (self) -> Self {
+        let token = self.grow_exp();
+        if let DslValue::Exp(depth, source) = token.value() {
+            if depth > 0 {
+                token.with_value(DslValue::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))
+    })
+}
+
+pub const fn peek_src <'src> (source: &'src str) -> Option<Cst<'src>> {
+    use DslValue::*;
+    let mut token: Cst<'src> = Cst::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(),
+            '(' =>
+                Cst::new(source, start, 1, Exp(1, SourceIter::new(str_range(source, start, start + 1)))),
+            '"' =>
+                Cst::new(source, start, 1, Str(str_range(source, start, start + 1))),
+            ':'|'@' =>
+                Cst::new(source, start, 1, Sym(str_range(source, start, start + 1))),
+            '/'|'a'..='z' =>
+                Cst::new(source, start, 1, Key(str_range(source, start, start + 1))),
+            '0'..='9' =>
+                Cst::new(source, start, 1, match to_digit(c) {
+                    Ok(c) => DslValue::Num(c),
+                    Result::Err(e) => DslValue::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),
+    }
+}
+
+/// Owns a reference to the source text.
+/// [SourceConstIter::next] emits subsequent pairs of:
+/// * a [Cst] 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<'src>(pub &'src str);
+
+impl<'src> From<SourceConstIter<'src>> for SourceIter<'src> {
+    fn from (source: SourceConstIter<'src>) -> Self{
+        Self(source)
+    }
+}
+
+impl<'src> From<&'src str> for SourceConstIter<'src> {
+    fn from (source: &'src str) -> Self{
+        Self::new(source)
+    }
+}
+
+impl<'src> SourceConstIter<'src> {
+    pub const fn new (source: &'src 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<(Cst<'src>, Self)> {
+        Self::next_mut(&mut self)
+    }
+    pub const fn peek (&self) -> Option<Cst<'src>> {
+        peek_src(self.0)
+    }
+    pub const fn next_mut (&mut self) -> Option<(Cst<'src>, Self)> {
+        match self.peek() {
+            Some(token) => Some((token, self.chomp(token.end()))),
+            None => None
+        }
+    }
+}
+
+const_iter!(<'src>|self: SourceConstIter<'src>| => Cst<'src> => self.next_mut().map(|(result, _)|result));
+
+/// Provides a native [Iterator] API over [SourceConstIter],
+/// emitting [Cst] items.
+///
+/// [Cst::next] returns just the [Cst] 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<'src>(pub SourceConstIter<'src>);
+
+impl<'src> SourceIter<'src> {
+    pub const fn new (source: &'src str) -> Self {
+        Self(SourceConstIter::new(source))
+    }
+    pub const fn peek (&self) -> Option<Cst<'src>> {
+        self.0.peek()
+    }
+}
+
+impl<'src> Iterator for SourceIter<'src> {
+    type Item = Cst<'src>;
+    fn next (&mut self) -> Option<Cst<'src>> {
+        self.0.next().map(|(item, rest)|{
+            self.0 = rest;
+            item
+        })
+    }
+}
+
+impl<'src> From<&'src str> for SourceIter<'src> {
+    fn from (source: &'src str) -> Self{
+        Self(SourceConstIter(source))
+    }
+}
+
+impl<'src> Into<Vec<Cst<'src>>> for SourceIter<'src> {
+    fn into (self) -> Vec<Cst<'src>> {
+        self.collect()
+    }
+}
+
+impl<'src> Into<Vec<Ast>> for SourceIter<'src> {
+    fn into (self) -> Vec<Ast> {
+        self.map(Into::into).collect()
+    }
+}