rebel-parse, rebel-lang: a unit should be an empty tuple

The empty tuple becomes the representation of the unit. An empty struct
is still another way to construct a unit, but never stored as a struct.

3 files changed, 45 insertions, 36 deletions

diff --git a/crates/rebel-lang/src/typing.rs b/crates/rebel-lang/src/typing.rs
index 0af7fcb..ceb3770 100644
--- a/crates/rebel-lang/src/typing.rs
+++ b/crates/rebel-lang/src/typing.rs
@@ -55,7 +55,7 @@ pub enum Type {
 
 impl Type {
 	pub fn unit() -> Self {
-		Type::Struct(Default::default())
+		Type::Tuple(Vec::new())
 	}
 
 	#[allow(clippy::only_used_in_recursion)]
@@ -535,14 +535,19 @@ impl<'scope> Context<'scope> {
 				)?;
 				Type::Map(key.try_into()?, Box::new(value))
 			}
-			Literal::Struct(entries) => Struct(
-				entries
-					.iter()
-					.map(|expr::StructField { name, value }| {
-						Ok((name.as_ref().to_owned(), self.type_expr(value)?))
-					})
-					.collect::<Result<_>>()?,
-			),
+			Literal::Struct(entries) => {
+				if entries.is_empty() {
+					return Ok(Type::unit());
+				}
+				Struct(
+					entries
+						.iter()
+						.map(|expr::StructField { name, value }| {
+							Ok((name.as_ref().to_owned(), self.type_expr(value)?))
+						})
+						.collect::<Result<_>>()?,
+				)
+			}
 		})
 	}
 
@@ -675,14 +680,19 @@ impl<'scope, T> TypeContext<'scope, T> {
 				self.type_type(key)?.try_into()?,
 				Box::new(self.type_type(value)?),
 			),
-			Literal::Struct(entries) => Struct(
-				entries
-					.iter()
-					.map(|typ::StructField { name, typ }| {
-						Ok((name.as_ref().to_owned(), self.type_type(typ)?))
-					})
-					.collect::<Result<_>>()?,
-			),
+			Literal::Struct(entries) => {
+				if entries.is_empty() {
+					return Ok(Type::unit());
+				}
+				Struct(
+					entries
+						.iter()
+						.map(|typ::StructField { name, typ }| {
+							Ok((name.as_ref().to_owned(), self.type_type(typ)?))
+						})
+						.collect::<Result<_>>()?,
+				)
+			}
 		})
 	}
 
@@ -724,7 +734,7 @@ impl Display for Type {
 					first = false;
 					elem.fmt(f)?;
 				}
-				if elems.len() < 2 {
+				if elems.len() == 1 {
 					f.write_str(",")?;
 				}
 				f.write_str(")")
@@ -732,9 +742,6 @@ impl Display for Type {
 			Type::Array(typ) => write!(f, "[{typ}]"),
 			Type::Map(key, value) => write!(f, "map{{{key} => {value}}}"),
 			Type::Struct(entries) => {
-				if entries.is_empty() {
-					return f.write_str("()");
-				}
 				let mut first = true;
 				f.write_str("{")?;
 				for (key, typ) in entries {
diff --git a/crates/rebel-lang/src/value.rs b/crates/rebel-lang/src/value.rs
index e9afddc..a08a1d8 100644
--- a/crates/rebel-lang/src/value.rs
+++ b/crates/rebel-lang/src/value.rs
@@ -32,7 +32,7 @@ pub enum Value {
 
 impl Value {
 	pub fn unit() -> Self {
-		Value::Struct(Default::default())
+		Value::Tuple(Vec::new())
 	}
 
 	pub fn typ(&self) -> Result<Type> {
@@ -457,14 +457,19 @@ impl<'scope> Context<'scope> {
 				}
 				Map(map)
 			}
-			Literal::Struct(entries) => Struct(
-				entries
-					.iter()
-					.map(|expr::StructField { name, value }| {
-						Ok((name.as_ref().to_owned(), self.eval_expr(value)?))
-					})
-					.collect::<Result<_>>()?,
-			),
+			Literal::Struct(entries) => {
+				if entries.is_empty() {
+					return Ok(Value::unit());
+				}
+				Struct(
+					entries
+						.iter()
+						.map(|expr::StructField { name, value }| {
+							Ok((name.as_ref().to_owned(), self.eval_expr(value)?))
+						})
+						.collect::<Result<_>>()?,
+				)
+			}
 		})
 	}
 
@@ -562,7 +567,7 @@ impl Display for Value {
 					first = false;
 					elem.fmt(f)?;
 				}
-				if elems.len() < 2 {
+				if elems.len() == 1 {
 					f.write_str(",")?;
 				}
 				f.write_str(")")
@@ -594,9 +599,6 @@ impl Display for Value {
 				f.write_str("}")
 			}
 			Value::Struct(entries) => {
-				if entries.is_empty() {
-					return f.write_str("()");
-				}
 				let mut first = true;
 				f.write_str("{")?;
 				for (key, value) in entries {
diff --git a/crates/rebel-parse/src/grammar/recipe.rs b/crates/rebel-parse/src/grammar/recipe.rs
index 9b1b50b..f0605e4 100644
--- a/crates/rebel-parse/src/grammar/recipe.rs
+++ b/crates/rebel-parse/src/grammar/recipe.rs
@@ -81,7 +81,7 @@ peg::parser! {
 
 		rule typ_literal() -> typ::Literal<'a>
 			= p('(') p(')') { typ::Literal::Unit }
-			/ p('(') elements:(typ() ** p(',')) p(',')? p(')') {
+			/ p('(') elements:(typ() ++ p(',')) p(',')? p(')') {
 				typ::Literal::Tuple(elements)
 			}
 			/ p('[') typ:typ() p(']') {
@@ -187,7 +187,7 @@ peg::parser! {
 				Ok(expr::Literal::Str{ pieces, kind: *kind })
 			}
 			/ p('(') p(')') { expr::Literal::Unit }
-			/ p('(') elements:(expr() ** p(',')) p(',')? p(')') {
+			/ p('(') elements:(expr() ++ p(',')) p(',')? p(')') {
 				expr::Literal::Tuple(elements)
 			}
 			/ p('[') elements:delimited(<expr()>, <p(',')>) p(']') {