wip: ast/cst

dsl/src/dsl_ast.rs

@@ -0,0 +1,70 @@
+use crate::*;
+use std::sync::Arc;
+use std::fmt::{Debug, Display, Formatter};
+
+/// Emits tokens.
+pub trait Ast: Debug {
+    fn peek (&self) -> Option<AstValue>;
+    fn next (&mut self) -> Option<AstValue>;
+    fn rest (self) -> Option<Box<dyn Ast>>;
+}
+
+/// A [Cst] can be used as an [Ast].
+impl<'source: 'static> Ast for Cst<'source> {
+    fn peek (&self) -> Option<AstValue> {
+        Cst::peek(self).map(|token|token.value.into())
+    }
+    fn next (&mut self) -> Option<AstValue> {
+        Iterator::next(self).map(|token|token.value.into())
+    }
+    fn rest (self) -> Option<Box<dyn Ast>> {
+        self.peek().is_some().then(||Box::new(self) as Box<dyn Ast>)
+    }
+}
+
+#[derive(Clone, Default, Debug)]
+pub enum AstValue {
+    #[default] Nil,
+    Err(DslError),
+    Num(usize),
+    Sym(Arc<str>),
+    Key(Arc<str>),
+    Str(Arc<str>),
+    Exp(Arc<Box<dyn Ast>>),
+}
+
+impl std::fmt::Display for AstValue {
+    fn fmt (&self, out: &mut Formatter) -> Result<(), std::fmt::Error> {
+        use AstValue::*;
+        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 AstValue {
+    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())),
+        }
+    }
+}
+
+impl<'source: 'static> Into<Box<dyn Ast>> for Cst<'source> {
+    fn into (self) -> Box<dyn Ast> {
+        Box::new(self)
+    }
+}