1 files changed, 93 insertions, 0 deletions
diff --git a/serde_dhall/src/static_type.rs b/serde_dhall/src/static_type.rs
new file mode 100644
index 0000000..13d5d70
--- /dev/null
+++ b/serde_dhall/src/static_type.rs
@@ -0,0 +1,93 @@
+use dhall_syntax::{Builtin, Integer, Natural};
+
+use crate::Type;
+
+/// A Rust type that can be represented as a Dhall type.
+///
+/// A typical example is `Option<bool>`,
+/// represented by the dhall expression `Optional Bool`.
+///
+/// This trait can and should be automatically derived.
+///
+/// The representation needs to be independent of the value.
+/// For this reason, something like `HashMap<String, bool>` cannot implement
+/// [StaticType] because each different value would
+/// have a different Dhall record type.
+pub trait StaticType {
+    fn static_type() -> Type;
+}
+
+macro_rules! derive_builtin {
+    ($ty:ty, $builtin:ident) => {
+        impl StaticType for $ty {
+            fn static_type() -> Type {
+                Type::make_builtin_type(Builtin::$builtin)
+            }
+        }
+    };
+}
+
+derive_builtin!(bool, Bool);
+derive_builtin!(Natural, Natural);
+derive_builtin!(u64, Natural);
+derive_builtin!(Integer, Integer);
+derive_builtin!(String, Text);
+
+impl<A, B> StaticType for (A, B)
+where
+    A: StaticType,
+    B: StaticType,
+{
+    fn static_type() -> Type {
+        Type::make_record_type(
+            vec![
+                ("_1".to_owned(), A::static_type()),
+                ("_2".to_owned(), B::static_type()),
+            ]
+            .into_iter(),
+        )
+    }
+}
+
+impl<T, E> StaticType for std::result::Result<T, E>
+where
+    T: StaticType,
+    E: StaticType,
+{
+    fn static_type() -> Type {
+        Type::make_union_type(
+            vec![
+                ("Ok".to_owned(), Some(T::static_type())),
+                ("Err".to_owned(), Some(E::static_type())),
+            ]
+            .into_iter(),
+        )
+    }
+}
+
+impl<T> StaticType for Option<T>
+where
+    T: StaticType,
+{
+    fn static_type() -> Type {
+        Type::make_optional_type(T::static_type())
+    }
+}
+
+impl<T> StaticType for Vec<T>
+where
+    T: StaticType,
+{
+    fn static_type() -> Type {
+        Type::make_list_type(T::static_type())
+    }
+}
+
+impl<'a, T> StaticType for &'a T
+where
+    T: StaticType,
+{
+    fn static_type() -> Type {
+        T::static_type()
+    }
+}