1 files changed, 114 insertions, 0 deletions
diff --git a/crates/typst-library/src/foundations/none.rs b/crates/typst-library/src/foundations/none.rs
new file mode 100644
index 00000000..d376c0c5
--- /dev/null
+++ b/crates/typst-library/src/foundations/none.rs
@@ -0,0 +1,114 @@
+use std::fmt::{self, Debug, Formatter};
+
+use ecow::EcoString;
+use serde::{Serialize, Serializer};
+
+use crate::diag::HintedStrResult;
+use crate::foundations::{
+    cast, ty, CastInfo, FromValue, IntoValue, Reflect, Repr, Type, Value,
+};
+
+/// A value that indicates the absence of any other value.
+///
+/// The none type has exactly one value: `{none}`.
+///
+/// When inserted into the document, it is not visible. This is also the value
+/// that is produced by empty code blocks. It can be
+/// [joined]($scripting/#blocks) with any value, yielding the other value.
+///
+/// # Example
+/// ```example
+/// Not visible: #none
+/// ```
+#[ty(cast, name = "none")]
+#[derive(Default, Copy, Clone, Eq, PartialEq, Ord, PartialOrd, Hash)]
+pub struct NoneValue;
+
+impl Reflect for NoneValue {
+    fn input() -> CastInfo {
+        CastInfo::Type(Type::of::<Self>())
+    }
+
+    fn output() -> CastInfo {
+        CastInfo::Type(Type::of::<Self>())
+    }
+
+    fn castable(value: &Value) -> bool {
+        matches!(value, Value::None)
+    }
+}
+
+impl IntoValue for NoneValue {
+    fn into_value(self) -> Value {
+        Value::None
+    }
+}
+
+impl FromValue for NoneValue {
+    fn from_value(value: Value) -> HintedStrResult<Self> {
+        match value {
+            Value::None => Ok(Self),
+            _ => Err(Self::error(&value)),
+        }
+    }
+}
+
+impl Debug for NoneValue {
+    fn fmt(&self, f: &mut Formatter) -> fmt::Result {
+        f.pad("None")
+    }
+}
+
+impl Repr for NoneValue {
+    fn repr(&self) -> EcoString {
+        "none".into()
+    }
+}
+
+impl Serialize for NoneValue {
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: Serializer,
+    {
+        serializer.serialize_none()
+    }
+}
+
+cast! {
+    (),
+    self => Value::None,
+    _: NoneValue => (),
+}
+
+impl<T: Reflect> Reflect for Option<T> {
+    fn input() -> CastInfo {
+        T::input() + NoneValue::input()
+    }
+
+    fn output() -> CastInfo {
+        T::output() + NoneValue::output()
+    }
+
+    fn castable(value: &Value) -> bool {
+        NoneValue::castable(value) || T::castable(value)
+    }
+}
+
+impl<T: IntoValue> IntoValue for Option<T> {
+    fn into_value(self) -> Value {
+        match self {
+            Some(v) => v.into_value(),
+            None => Value::None,
+        }
+    }
+}
+
+impl<T: FromValue> FromValue for Option<T> {
+    fn from_value(value: Value) -> HintedStrResult<Self> {
+        match value {
+            Value::None => Ok(None),
+            v if T::castable(&v) => Ok(Some(T::from_value(v)?)),
+            _ => Err(Self::error(&value)),
+        }
+    }
+}