None literal 🕳

src/eval/mod.rs

@@ -176,6 +176,7 @@ impl Eval for Spanned<&Lit> {
                     Value::Error
                 }
             },
+            Lit::None => Value::None,
             Lit::Bool(v) => Value::Bool(v),
             Lit::Int(v) => Value::Int(v),
             Lit::Float(v) => Value::Float(v),

src/parse/mod.rs

@@ -326,6 +326,7 @@ fn value(p: &mut Parser) -> Option<Expr> {
         }
 
         // Basic values.
+        Some(Token::None) => Expr::Lit(Lit::None),
         Some(Token::Bool(b)) => Expr::Lit(Lit::Bool(b)),
         Some(Token::Int(i)) => Expr::Lit(Lit::Int(i)),
         Some(Token::Float(f)) => Expr::Lit(Lit::Float(f)),

src/parse/tests.rs

@@ -614,6 +614,7 @@ fn test_parse_values() {
     t!("{name}"   Block(Id("name")));
     t!("{ke-bab}" Block(Id("ke-bab")));
     t!("{α}"      Block(Id("α")));
+    t!("{none}"   Block(Expr::Lit(Lit::None)));
     t!("{true}"   Block(Bool(true)));
     t!("{false}"  Block(Bool(false)));
     t!("{1.0e-4}" Block(Float(1e-4)));

src/parse/tokens.rs

@@ -294,6 +294,7 @@ impl<'s> Tokens<'s> {
         self.s.eat_while(is_id_continue);
         let string = self.s.eaten_from(start);
         match string {
+            "none" => Token::None,
             "true" => Token::Bool(true),
             "false" => Token::Bool(false),
             _ => Token::Ident(string),
@@ -377,6 +378,7 @@ mod tests {
     use super::*;
     use crate::parse::tests::check;
 
+    use Option::None;
     use Token::{
         BlockComment as BC, Ident as Id, LeftBrace as LB, LeftBracket as L,
         LeftParen as LP, LineComment as LC, RightBrace as RB, RightBracket as R,
@@ -679,7 +681,11 @@ mod tests {
     }
 
     #[test]
-    fn test_tokenize_bools() {
+    fn test_tokenize_keywords() {
+        // Test none.
+        t!(Header[" /"]: "none" => Token::None);
+        t!(Header[" /"]: "None" => Id("None"));
+
         // Test valid bools.
         t!(Header[" /"]: "false" => Bool(false));
         t!(Header[" /"]: "true"  => Bool(true));

src/syntax/expr.rs

@@ -108,6 +108,8 @@ pub type ExprContent = Tree;
 pub enum Lit {
     /// A identifier literal: `left`.
     Ident(Ident),
+    /// The none literal: `none`.
+    None,
     /// A boolean literal: `true`, `false`.
     Bool(bool),
     /// An integer literal: `120`.

src/syntax/token.rs

@@ -63,6 +63,8 @@ pub enum Token<'s> {
 
     /// An identifier: `center`.
     Ident(&'s str),
+    /// A none: `none`.
+    None,
     /// A boolean: `true`, `false`.
     Bool(bool),
     /// An integer: `120`.
@@ -152,6 +154,7 @@ impl<'s> Token<'s> {
             Self::Slash => "slash",
 
             Self::Ident(_) => "identifier",
+            Self::None => "none",
             Self::Bool(_) => "bool",
             Self::Int(_) => "integer",
             Self::Float(_) => "float",