Implement serialization

12 files changed, 725 insertions, 72 deletions

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 5329eca..0fe7814 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -2,6 +2,7 @@
 
 #### [Unreleased]
 
+- Implement serialization (https://github.com/Nadrieril/dhall-rust/issues/164)
 - BREAKING CHANGE: use u64/i64 instead of usize/isize in `NumKind`
 
 #### [0.7.5] - 2020-10-28
diff --git a/serde_dhall/src/deserialize.rs b/serde_dhall/src/deserialize.rs
index 12b4703..0e518ea 100644
--- a/serde_dhall/src/deserialize.rs
+++ b/serde_dhall/src/deserialize.rs
@@ -47,8 +47,6 @@ pub trait FromDhall: Sealed + Sized {
 
 impl<T> Sealed for T where T: serde::de::DeserializeOwned {}
 
-struct Deserializer<'a>(Cow<'a, SimpleValue>);
-
 /// Deserialize a Rust value from a Dhall [`SimpleValue`].
 ///
 /// # Example
@@ -109,6 +107,8 @@ where
     }
 }
 
+struct Deserializer<'a>(Cow<'a, SimpleValue>);
+
 impl<'de: 'a, 'a> serde::de::IntoDeserializer<'de, Error> for Deserializer<'a> {
     type Deserializer = Deserializer<'a>;
     fn into_deserializer(self) -> Self::Deserializer {
@@ -171,9 +171,19 @@ impl<'de: 'a, 'a> serde::Deserializer<'de> for Deserializer<'a> {
         }
     }
 
+    fn deserialize_unit<V>(self, visitor: V) -> crate::Result<V::Value>
+    where
+        V: serde::de::Visitor<'de>,
+    {
+        match self.0.as_ref() {
+            SimpleValue::Record(m) if m.is_empty() => visitor.visit_unit(),
+            _ => self.deserialize_any(visitor),
+        }
+    }
+
     serde::forward_to_deserialize_any! {
         bool i8 i16 i32 i64 i128 u8 u16 u32 u64 u128 f32 f64 char str string
-        bytes byte_buf option unit unit_struct newtype_struct seq
+        bytes byte_buf option unit_struct newtype_struct seq
         tuple_struct map struct enum identifier ignored_any
     }
 }
diff --git a/serde_dhall/src/error.rs b/serde_dhall/src/error.rs
index 896e8b9..3309fe4 100644
--- a/serde_dhall/src/error.rs
+++ b/serde_dhall/src/error.rs
@@ -11,6 +11,7 @@ pub struct Error(pub(crate) ErrorKind);
 pub(crate) enum ErrorKind {
     Dhall(DhallError),
     Deserialize(String),
+    Serialize(String),
 }
 
 impl From<ErrorKind> for Error {
@@ -24,6 +25,7 @@ impl std::fmt::Display for Error {
         match &self.0 {
             ErrorKind::Dhall(err) => write!(f, "{}", err),
             ErrorKind::Deserialize(err) => write!(f, "{}", err),
+            ErrorKind::Serialize(err) => write!(f, "{}", err),
         }
     }
 }
@@ -38,3 +40,12 @@ impl serde::de::Error for Error {
         ErrorKind::Deserialize(msg.to_string()).into()
     }
 }
+
+impl serde::ser::Error for Error {
+    fn custom<T>(msg: T) -> Self
+    where
+        T: std::fmt::Display,
+    {
+        ErrorKind::Serialize(msg.to_string()).into()
+    }
+}
diff --git a/serde_dhall/src/lib.rs b/serde_dhall/src/lib.rs
index 8291f74..e236e37 100644
--- a/serde_dhall/src/lib.rs
+++ b/serde_dhall/src/lib.rs
@@ -169,6 +169,7 @@ mod test_readme {
 mod deserialize;
 mod error;
 mod options;
+mod serialize;
 mod static_type;
 /// Dhall values
 mod value;
@@ -176,10 +177,11 @@ mod value;
 #[doc(hidden)]
 pub use dhall_proc_macros::StaticType;
 
-pub(crate) use deserialize::Sealed;
 pub use deserialize::{from_simple_value, FromDhall};
 pub(crate) use error::ErrorKind;
 pub use error::{Error, Result};
-pub use options::{from_file, from_str, Deserializer};
+pub use options::de::{from_file, from_str, Deserializer};
+pub use options::ser::{serialize, Serializer};
+pub use serialize::ToDhall;
 pub use static_type::StaticType;
 pub use value::{NumKind, SimpleType, SimpleValue, Value};
diff --git a/serde_dhall/src/options.rs b/serde_dhall/src/options/de.rs
index 7b27114..8ff794d 100644
--- a/serde_dhall/src/options.rs
+++ b/serde_dhall/src/options/de.rs
@@ -19,20 +19,20 @@ pub struct ManualAnnot<'ty>(&'ty SimpleType);
 #[derive(Debug, Clone, Copy)]
 pub struct StaticAnnot;
 
-pub trait HasAnnot<A> {
+pub trait OptionalAnnot<A> {
     fn get_annot(a: &A) -> Option<SimpleType>;
 }
-impl<T> HasAnnot<NoAnnot> for T {
+impl<T> OptionalAnnot<NoAnnot> for T {
     fn get_annot(_: &NoAnnot) -> Option<SimpleType> {
         None
     }
 }
-impl<'ty, T> HasAnnot<ManualAnnot<'ty>> for T {
+impl<'ty, T> OptionalAnnot<ManualAnnot<'ty>> for T {
     fn get_annot(a: &ManualAnnot<'ty>) -> Option<SimpleType> {
         Some(a.0.clone())
     }
 }
-impl<T: StaticType> HasAnnot<StaticAnnot> for T {
+impl<T: StaticType> OptionalAnnot<StaticAnnot> for T {
     fn get_annot(_: &StaticAnnot) -> Option<SimpleType> {
         Some(T::static_type())
     }
@@ -252,7 +252,7 @@ impl<'a, A> Deserializer<'a, A> {
 
     fn _parse<T>(&self) -> dhall::error::Result<Value>
     where
-        T: HasAnnot<A>,
+        T: OptionalAnnot<A>,
     {
         let parsed = match &self.source {
             Source::Str(s) => Parsed::parse_str(s)?,
@@ -287,7 +287,7 @@ impl<'a, A> Deserializer<'a, A> {
     /// [`StaticType`]: trait.StaticType.html
     pub fn parse<T>(&self) -> Result<T>
     where
-        T: FromDhall + HasAnnot<A>,
+        T: FromDhall + OptionalAnnot<A>,
     {
         let val = self
             ._parse::<T>()
diff --git a/serde_dhall/src/options/mod.rs b/serde_dhall/src/options/mod.rs
new file mode 100644
index 0000000..384f318
--- /dev/null
+++ b/serde_dhall/src/options/mod.rs
@@ -0,0 +1,2 @@
+pub(crate) mod de;
+pub(crate) mod ser;
diff --git a/serde_dhall/src/options/ser.rs b/serde_dhall/src/options/ser.rs
new file mode 100644
index 0000000..026dd21
--- /dev/null
+++ b/serde_dhall/src/options/ser.rs
@@ -0,0 +1,67 @@
+use crate::{Result, SimpleType, StaticType, ToDhall};
+
+#[derive(Debug, Clone, Copy)]
+pub struct NoAnnot;
+#[derive(Debug, Clone, Copy)]
+pub struct ManualAnnot<'ty>(&'ty SimpleType);
+#[derive(Debug, Clone, Copy)]
+pub struct StaticAnnot;
+
+pub trait RequiredAnnot<A> {
+    fn get_annot(a: &A) -> SimpleType;
+}
+impl<'ty, T> RequiredAnnot<ManualAnnot<'ty>> for T {
+    fn get_annot(a: &ManualAnnot<'ty>) -> SimpleType {
+        a.0.clone()
+    }
+}
+impl<T: StaticType> RequiredAnnot<StaticAnnot> for T {
+    fn get_annot(_: &StaticAnnot) -> SimpleType {
+        T::static_type()
+    }
+}
+
+#[derive(Debug, Clone)]
+pub struct Serializer<'a, T, A> {
+    data: &'a T,
+    annot: A,
+}
+
+impl<'a, T> Serializer<'a, T, NoAnnot> {
+    pub fn type_annotation<'ty>(
+        self,
+        ty: &'ty SimpleType,
+    ) -> Serializer<'a, T, ManualAnnot<'ty>> {
+        Serializer {
+            annot: ManualAnnot(ty),
+            data: self.data,
+        }
+    }
+
+    pub fn static_type_annotation(self) -> Serializer<'a, T, StaticAnnot> {
+        Serializer {
+            annot: StaticAnnot,
+            data: self.data,
+        }
+    }
+}
+
+impl<'a, T, A> Serializer<'a, T, A> {
+    pub fn to_string(&self) -> Result<String>
+    where
+        T: ToDhall + RequiredAnnot<A>,
+    {
+        let val = self.data.to_dhall(&T::get_annot(&self.annot))?;
+        Ok(val.to_string())
+    }
+}
+
+pub fn serialize<'a, T>(data: &'a T) -> Serializer<'a, T, NoAnnot>
+where
+    T: ToDhall,
+{
+    Serializer {
+        data,
+        annot: NoAnnot,
+    }
+}
diff --git a/serde_dhall/src/serialize.rs b/serde_dhall/src/serialize.rs
new file mode 100644
index 0000000..dd3e426
--- /dev/null
+++ b/serde_dhall/src/serialize.rs
@@ -0,0 +1,312 @@
+use serde::ser;
+use std::collections::BTreeMap;
+
+use dhall::syntax::NumKind;
+
+use crate::value::SimpleValue;
+use crate::{Error, ErrorKind, Result, SimpleType, Value};
+use SimpleValue::*;
+
+pub trait Sealed {}
+
+pub trait ToDhall: Sealed {
+    #[doc(hidden)]
+    fn to_dhall(&self, ty: &SimpleType) -> Result<Value>;
+}
+
+impl<T> Sealed for T where T: ser::Serialize {}
+
+impl<T> ToDhall for T
+where
+    T: ser::Serialize,
+{
+    fn to_dhall(&self, ty: &SimpleType) -> Result<Value> {
+        let sval: SimpleValue = self.serialize(Serializer)?;
+        sval.into_value(ty)
+    }
+}
+
+#[derive(Default, Clone, Copy)]
+struct Serializer;
+
+impl ser::Serializer for Serializer {
+    type Ok = SimpleValue;
+    type Error = Error;
+
+    type SerializeSeq = SeqSerializer;
+    type SerializeTuple = TupleSerializer;
+    type SerializeTupleStruct = ser::Impossible<Self::Ok, Self::Error>;
+    type SerializeTupleVariant = ser::Impossible<Self::Ok, Self::Error>;
+    type SerializeMap = MapSerializer;
+    type SerializeStruct = StructSerializer;
+    type SerializeStructVariant = ser::Impossible<Self::Ok, Self::Error>;
+
+    fn serialize_bool(self, v: bool) -> Result<Self::Ok> {
+        Ok(Num(NumKind::Bool(v)))
+    }
+
+    fn serialize_i8(self, v: i8) -> Result<Self::Ok> {
+        self.serialize_i64(i64::from(v))
+    }
+    fn serialize_i16(self, v: i16) -> Result<Self::Ok> {
+        self.serialize_i64(i64::from(v))
+    }
+    fn serialize_i32(self, v: i32) -> Result<Self::Ok> {
+        self.serialize_i64(i64::from(v))
+    }
+    fn serialize_i64(self, v: i64) -> Result<Self::Ok> {
+        Ok(Num(NumKind::Integer(v)))
+    }
+
+    fn serialize_u8(self, v: u8) -> Result<Self::Ok> {
+        self.serialize_u64(u64::from(v))
+    }
+    fn serialize_u16(self, v: u16) -> Result<Self::Ok> {
+        self.serialize_u64(u64::from(v))
+    }
+    fn serialize_u32(self, v: u32) -> Result<Self::Ok> {
+        self.serialize_u64(u64::from(v))
+    }
+    fn serialize_u64(self, v: u64) -> Result<Self::Ok> {
+        Ok(Num(NumKind::Natural(v)))
+    }
+
+    fn serialize_f32(self, v: f32) -> Result<Self::Ok> {
+        self.serialize_f64(f64::from(v))
+    }
+    fn serialize_f64(self, v: f64) -> Result<Self::Ok> {
+        Ok(Num(NumKind::Double(v.into())))
+    }
+
+    fn serialize_char(self, v: char) -> Result<Self::Ok> {
+        self.serialize_str(&v.to_string())
+    }
+    fn serialize_str(self, v: &str) -> Result<Self::Ok> {
+        Ok(Text(v.to_owned()))
+    }
+
+    fn serialize_bytes(self, _v: &[u8]) -> Result<Self::Ok> {
+        Err(ErrorKind::Serialize(
+            "Unsupported data for serialization: byte array".to_owned(),
+        )
+        .into())
+    }
+
+    fn serialize_none(self) -> Result<Self::Ok> {
+        Ok(Optional(None))
+    }
+    fn serialize_some<T>(self, v: &T) -> Result<Self::Ok>
+    where
+        T: ?Sized + ser::Serialize,
+    {
+        Ok(Optional(Some(Box::new(v.serialize(self)?))))
+    }
+
+    fn serialize_unit(self) -> Result<Self::Ok> {
+        Ok(Record(Default::default()))
+    }
+
+    fn serialize_unit_struct(self, _name: &'static str) -> Result<Self::Ok> {
+        self.serialize_unit()
+    }
+    fn serialize_newtype_struct<T>(
+        self,
+        _name: &'static str,
+        _value: &T,
+    ) -> Result<Self::Ok>
+    where
+        T: ?Sized + ser::Serialize,
+    {
+        Err(ErrorKind::Serialize(
+            "Unsupported data for serialization: newtype struct".to_owned(),
+        )
+        .into())
+    }
+    fn serialize_struct(
+        self,
+        _name: &'static str,
+        _len: usize,
+    ) -> Result<Self::SerializeStruct> {
+        Ok(StructSerializer::default())
+    }
+
+    fn serialize_unit_variant(
+        self,
+        _name: &'static str,
+        _variant_index: u32,
+        variant: &'static str,
+    ) -> Result<Self::Ok> {
+        Ok(Union(variant.to_owned(), None))
+    }
+    fn serialize_newtype_variant<T>(
+        self,
+        _name: &'static str,
+        _variant_index: u32,
+        variant: &'static str,
+        value: &T,
+    ) -> Result<Self::Ok>
+    where
+        T: ?Sized + ser::Serialize,
+    {
+        let value = value.serialize(self)?;
+        Ok(Union(variant.to_owned(), Some(Box::new(value))))
+    }
+    fn serialize_tuple_variant(
+        self,
+        _name: &'static str,
+        _variant_index: u32,
+        _variant: &'static str,
+        _len: usize,
+    ) -> Result<Self::SerializeTupleVariant> {
+        Err(ErrorKind::Serialize(
+            "Unsupported data for serialization: tuple variant".to_owned(),
+        )
+        .into())
+    }
+    fn serialize_struct_variant(
+        self,
+        _name: &'static str,
+        _variant_index: u32,
+        _variant: &'static str,
+        _len: usize,
+    ) -> Result<Self::SerializeStructVariant> {
+        Err(ErrorKind::Serialize(
+            "Unsupported data for serialization: struct variant".to_owned(),
+        )
+        .into())
+    }
+
+    fn serialize_tuple(self, _len: usize) -> Result<Self::SerializeTuple> {
+        Ok(TupleSerializer::default())
+    }
+    fn serialize_tuple_struct(
+        self,
+        _name: &'static str,
+        _len: usize,
+    ) -> Result<Self::SerializeTupleStruct> {
+        Err(ErrorKind::Serialize(
+            "Unsupported data for serialization: tuple struct".to_owned(),
+        )
+        .into())
+    }
+
+    fn serialize_seq(self, _len: Option<usize>) -> Result<Self::SerializeSeq> {
+        Ok(SeqSerializer::default())
+    }
+
+    fn serialize_map(self, _len: Option<usize>) -> Result<Self::SerializeMap> {
+        Ok(MapSerializer::default())
+    }
+}
+
+#[derive(Default)]
+struct SeqSerializer(Vec<SimpleValue>);
+
+impl ser::SerializeSeq for SeqSerializer {
+    type Ok = SimpleValue;
+    type Error = Error;
+
+    fn serialize_element<T>(&mut self, value: &T) -> Result<()>
+    where
+        T: ?Sized + ser::Serialize,
+    {
+        self.0.push(value.serialize(Serializer)?);
+        Ok(())
+    }
+
+    fn end(self) -> Result<Self::Ok> {
+        Ok(List(self.0))
+    }
+}
+
+#[derive(Default)]
+struct TupleSerializer(Vec<SimpleValue>);
+
+impl ser::SerializeTuple for TupleSerializer {
+    type Ok = SimpleValue;
+    type Error = Error;
+
+    fn serialize_element<T>(&mut self, value: &T) -> Result<()>
+    where
+        T: ?Sized + ser::Serialize,
+    {
+        self.0.push(value.serialize(Serializer)?);
+        Ok(())
+    }
+
+    fn end(self) -> Result<Self::Ok> {
+        Ok(Record(
+            self.0
+                .into_iter()
+                .enumerate()
+                .map(|(i, x)| (format!("_{}", i + 1), x))
+                .collect(),
+        ))
+    }
+}
+
+#[derive(Default)]
+struct MapSerializer {
+    map: BTreeMap<String, SimpleValue>,
+    key: Option<String>,
+    val: Option<SimpleValue>,
+}
+
+impl ser::SerializeMap for MapSerializer {
+    type Ok = SimpleValue;
+    type Error = Error;
+
+    fn serialize_key<T>(&mut self, key: &T) -> Result<()>
+    where
+        T: ?Sized + ser::Serialize,
+    {
+        let key = match key.serialize(Serializer)? {
+            Text(key) => key,
+            _ => return Err(<Error as ser::Error>::custom("not a string")),
+        };
+        if let Some(val) = self.val.take() {
+            self.map.insert(key, val);
+        } else {
+            self.key = Some(key);
+        }
+        Ok(())
+    }
+
+    fn serialize_value<T>(&mut self, val: &T) -> Result<()>
+    where
+        T: ?Sized + ser::Serialize,
+    {
+        let val: SimpleValue = val.serialize(Serializer)?;
+        if let Some(key) = self.key.take() {
+            self.map.insert(key, val);
+        } else {
+            self.val = Some(val);
+        }
+        Ok(())
+    }
+
+    fn end(self) -> Result<Self::Ok> {
+        Ok(Record(self.map))
+    }
+}
+
+#[derive(Default)]
+struct StructSerializer(BTreeMap<String, SimpleValue>);
+
+impl ser::SerializeStruct for StructSerializer {
+    type Ok = SimpleValue;
+    type Error = Error;
+
+    fn serialize_field<T>(&mut self, key: &'static str, val: &T) -> Result<()>
+    where
+        T: ?Sized + ser::Serialize,
+    {
+        let val: SimpleValue = val.serialize(Serializer)?;
+        self.0.insert(key.into(), val);
+        Ok(())
+    }
+
+    fn end(self) -> Result<Self::Ok> {
+        Ok(Record(self.0))
+    }
+}
diff --git a/serde_dhall/src/static_type.rs b/serde_dhall/src/static_type.rs
index 3c5da18..7e6c27c 100644
--- a/serde_dhall/src/static_type.rs
+++ b/serde_dhall/src/static_type.rs
@@ -103,6 +103,26 @@ derive_builtin!(i32, Integer);
 derive_builtin!(f64, Double);
 derive_builtin!(f32, Double);
 derive_builtin!(String, Text);
+derive_builtin!(&str, Text);
+
+impl StaticType for () {
+    fn static_type() -> SimpleType {
+        SimpleType::Record(vec![].into_iter().collect())
+    }
+}
+
+impl<A> StaticType for (A,)
+where
+    A: StaticType,
+{
+    fn static_type() -> SimpleType {
+        SimpleType::Record(
+            vec![("_1".to_owned(), A::static_type())]
+                .into_iter()
+                .collect(),
+        )
+    }
+}
 
 impl<A, B> StaticType for (A, B)
 where
@@ -121,6 +141,46 @@ where
     }
 }
 
+impl<A, B, C> StaticType for (A, B, C)
+where
+    A: StaticType,
+    B: StaticType,
+    C: StaticType,
+{
+    fn static_type() -> SimpleType {
+        SimpleType::Record(
+            vec![
+                ("_1".to_owned(), A::static_type()),
+                ("_2".to_owned(), B::static_type()),
+                ("_3".to_owned(), C::static_type()),
+            ]
+            .into_iter()
+            .collect(),
+        )
+    }
+}
+
+impl<A, B, C, D> StaticType for (A, B, C, D)
+where
+    A: StaticType,
+    B: StaticType,
+    C: StaticType,
+    D: StaticType,
+{
+    fn static_type() -> SimpleType {
+        SimpleType::Record(
+            vec![
+                ("_1".to_owned(), A::static_type()),
+                ("_2".to_owned(), B::static_type()),
+                ("_3".to_owned(), C::static_type()),
+                ("_4".to_owned(), D::static_type()),
+            ]
+            .into_iter()
+            .collect(),
+        )
+    }
+}
+
 impl<T, E> StaticType for std::result::Result<T, E>
 where
     T: StaticType,
diff --git a/serde_dhall/src/value.rs b/serde_dhall/src/value.rs
index d7116d9..ca05658 100644
--- a/serde_dhall/src/value.rs
+++ b/serde_dhall/src/value.rs
@@ -6,7 +6,7 @@ use dhall::semantics::{Hir, HirKind, Nir, NirKind};
 pub use dhall::syntax::NumKind;
 use dhall::syntax::{Expr, ExprKind, Span};
 
-use crate::{Error, ErrorKind, FromDhall, Result, Sealed};
+use crate::{Error, ErrorKind, FromDhall, Result, ToDhall};
 
 #[doc(hidden)]
 /// An arbitrary Dhall value.
@@ -292,6 +292,94 @@ impl SimpleValue {
             _ => return None,
         })
     }
+
+    fn to_hir(&self, ty: &SimpleType) -> Result<Hir> {
+        use SimpleType as T;
+        use SimpleValue as V;
+        let hir = |k| Hir::new(HirKind::Expr(k), Span::Artificial);
+        let type_error = |msg| Error(ErrorKind::Serialize(msg));
+        let kind = match (self, ty) {
+            (V::Num(num @ NumKind::Bool(_)), T::Bool)
+            | (V::Num(num @ NumKind::Natural(_)), T::Natural)
+            | (V::Num(num @ NumKind::Integer(_)), T::Integer)
+            | (V::Num(num @ NumKind::Double(_)), T::Double) => {
+                ExprKind::Num(num.clone())
+            }
+            (V::Text(v), T::Text) => ExprKind::TextLit(v.clone().into()),
+            (V::Optional(None), T::Optional(t)) => ExprKind::Op(OpKind::App(
+                hir(ExprKind::Builtin(Builtin::OptionalNone)),
+                t.to_hir(),
+            )),
+            (V::Optional(Some(v)), T::Optional(t)) => {
+                ExprKind::SomeLit(v.to_hir(t)?)
+            }
+            (V::List(v), T::List(t)) if v.is_empty() => {
+                ExprKind::EmptyListLit(hir(ExprKind::Op(OpKind::App(
+                    hir(ExprKind::Builtin(Builtin::List)),
+                    t.to_hir(),
+                ))))
+            }
+            (V::List(v), T::List(t)) => ExprKind::NEListLit(
+                v.iter().map(|v| v.to_hir(t)).collect::<Result<_>>()?,
+            ),
+            (V::Record(v), T::Record(t)) => ExprKind::RecordLit(
+                v.iter()
+                    .map(|(k, v)| match t.get(k) {
+                        Some(t) => Ok((k.clone().into(), v.to_hir(t)?)),
+                        None => Err(type_error(format!(
+                            "expected a value of type {}, found {:?}",
+                            ty.to_hir().to_expr(Default::default()),
+                            self
+                        ))),
+                    })
+                    .collect::<Result<_>>()?,
+            ),
+            (V::Union(variant, Some(v)), T::Union(t)) => match t.get(variant) {
+                Some(Some(variant_t)) => ExprKind::Op(OpKind::App(
+                    hir(ExprKind::Op(OpKind::Field(
+                        ty.to_hir(),
+                        variant.clone().into(),
+                    ))),
+                    v.to_hir(variant_t)?,
+                )),
+                _ => {
+                    return Err(type_error(format!(
+                        "expected a value of type {}, found {:?}",
+                        ty.to_hir().to_expr(Default::default()),
+                        self
+                    )))
+                }
+            },
+            (V::Union(variant, None), T::Union(t)) => match t.get(variant) {
+                Some(None) => ExprKind::Op(OpKind::Field(
+                    ty.to_hir(),
+                    variant.clone().into(),
+                )),
+                _ => {
+                    return Err(type_error(format!(
+                        "expected a value of type {}, found {:?}",
+                        ty.to_hir().to_expr(Default::default()),
+                        self
+                    )))
+                }
+            },
+            _ => {
+                return Err(type_error(format!(
+                    "expected a value of type {}, found {:?}",
+                    ty.to_hir().to_expr(Default::default()),
+                    self
+                )))
+            }
+        };
+        Ok(hir(kind))
+    }
+    pub(crate) fn into_value(self, ty: &SimpleType) -> Result<Value> {
+        Ok(Value {
+            hir: self.to_hir(ty)?,
+            as_simple_val: Some(self),
+            as_simple_ty: None,
+        })
+    }
 }
 
 impl SimpleType {
@@ -376,8 +464,10 @@ impl SimpleType {
     }
 }
 
-impl Sealed for Value {}
-impl Sealed for SimpleType {}
+impl crate::deserialize::Sealed for Value {}
+impl crate::deserialize::Sealed for SimpleType {}
+impl crate::serialize::Sealed for Value {}
+impl crate::serialize::Sealed for SimpleValue {}
 
 impl FromDhall for Value {
     fn from_dhall(v: &Value) -> Result<Self> {
@@ -394,6 +484,16 @@ impl FromDhall for SimpleType {
         })
     }
 }
+impl ToDhall for Value {
+    fn to_dhall(&self, _ty: &SimpleType) -> Result<Value> {
+        Ok(self.clone())
+    }
+}
+impl ToDhall for SimpleValue {
+    fn to_dhall(&self, ty: &SimpleType) -> Result<Value> {
+        self.clone().into_value(ty)
+    }
+}
 
 impl Eq for Value {}
 impl PartialEq for Value {
diff --git a/serde_dhall/tests/de.rs b/serde_dhall/tests/de.rs
index 3abaad2..0b43de2 100644
--- a/serde_dhall/tests/de.rs
+++ b/serde_dhall/tests/de.rs
@@ -1,62 +1,5 @@
 use serde::Deserialize;
-use serde_dhall::{from_str, FromDhall, NumKind, SimpleValue, StaticType};
-
-#[test]
-fn test_de_typed() {
-    fn parse<T: FromDhall + StaticType>(s: &str) -> T {
-        from_str(s).static_type_annotation().parse().unwrap()
-    }
-
-    assert_eq!(parse::<bool>("True"), true);
-
-    assert_eq!(parse::<u64>("1"), 1);
-    assert_eq!(parse::<u32>("1"), 1);
-    assert_eq!(parse::<usize>("1"), 1);
-
-    assert_eq!(parse::<i64>("+1"), 1);
-    assert_eq!(parse::<i32>("+1"), 1);
-    assert_eq!(parse::<isize>("+1"), 1);
-
-    assert_eq!(parse::<f64>("1.0"), 1.0);
-    assert_eq!(parse::<f32>("1.0"), 1.0);
-
-    assert_eq!(parse::<String>(r#""foo""#), "foo".to_owned());
-    assert_eq!(parse::<Vec<u64>>("[] : List Natural"), <Vec<u64>>::new());
-    assert_eq!(parse::<Vec<u64>>("[1, 2]"), vec![1, 2]);
-    assert_eq!(parse::<Option<u64>>("None Natural"), None);
-    assert_eq!(parse::<Option<u64>>("Some 1"), Some(1));
-
-    assert_eq!(
-        parse::<(u64, String)>(r#"{ _1 = 1, _2 = "foo" }"#),
-        (1, "foo".to_owned())
-    );
-
-    #[derive(Debug, PartialEq, Eq, Deserialize, StaticType)]
-    struct Foo {
-        x: u64,
-        y: i64,
-    }
-    assert_eq!(parse::<Foo>("{ x = 1, y = -2 }"), Foo { x: 1, y: -2 });
-
-    #[derive(Debug, PartialEq, Eq, Deserialize, StaticType)]
-    enum Bar {
-        X(u64),
-        Y(i64),
-    }
-    assert_eq!(parse::<Bar>("< X: Natural | Y: Integer >.X 1"), Bar::X(1));
-
-    #[derive(Debug, PartialEq, Eq, Deserialize, StaticType)]
-    enum Baz {
-        X,
-        Y(i64),
-    }
-    assert_eq!(parse::<Baz>("< X | Y: Integer >.X"), Baz::X);
-
-    assert!(from_str("< X | Y: Integer >.Y")
-        .static_type_annotation()
-        .parse::<Baz>()
-        .is_err());
-}
+use serde_dhall::{from_str, FromDhall, NumKind, SimpleValue};
 
 #[test]
 fn test_de_untyped() {
diff --git a/serde_dhall/tests/serde.rs b/serde_dhall/tests/serde.rs
new file mode 100644
index 0000000..39f2f79
--- /dev/null
+++ b/serde_dhall/tests/serde.rs
@@ -0,0 +1,145 @@
+mod serde {
+    use serde::{Deserialize, Serialize};
+    use serde_dhall::{from_str, serialize, FromDhall, StaticType, ToDhall};
+
+    fn assert_de<T>(s: &str, x: T)
+    where
+        T: FromDhall + StaticType + PartialEq + std::fmt::Debug,
+    {
+        assert_eq!(
+            from_str(s)
+                .static_type_annotation()
+                .parse::<T>()
+                .map_err(|e| e.to_string()),
+            Ok(x)
+        );
+    }
+    fn assert_ser<T>(s: &str, x: T)
+    where
+        T: ToDhall + StaticType + PartialEq + std::fmt::Debug,
+    {
+        assert_eq!(
+            serialize(&x)
+                .static_type_annotation()
+                .to_string()
+                .map_err(|e| e.to_string()),
+            Ok(s.to_string())
+        );
+    }
+    fn assert_serde<T>(s: &str, x: T)
+    where
+        T: ToDhall
+            + FromDhall
+            + StaticType
+            + PartialEq
+            + std::fmt::Debug
+            + Clone,
+    {
+        assert_de(s, x.clone());
+        assert_ser(s, x);
+    }
+
+    #[test]
+    fn numbers() {
+        assert_serde("True", true);
+
+        assert_serde("1", 1u64);
+        assert_serde("1", 1u32);
+        assert_serde("1", 1usize);
+
+        assert_serde("+1", 1i64);
+        assert_serde("+1", 1i32);
+        assert_serde("+1", 1isize);
+
+        assert_serde("1.0", 1.0f64);
+        assert_serde("1.0", 1.0f32);
+    }
+
+    #[test]
+    fn text() {
+        assert_serde(r#""foo""#, "foo".to_owned());
+        assert_ser(r#""foo""#, "foo");
+    }
+
+    #[test]
+    fn list() {
+        assert_serde("[] : List Natural", <Vec<u64>>::new());
+        assert_serde("[] : List Text", <Vec<String>>::new());
+        assert_serde(
+            r#"["foo", "bar"]"#,
+            vec!["foo".to_owned(), "bar".to_owned()],
+        );
+        assert_ser(r#"["foo", "bar"]"#, vec!["foo", "bar"]);
+        assert_serde::<Vec<u64>>("[1, 2]", vec![1, 2]);
+    }
+
+    #[test]
+    fn optional() {
+        assert_serde::<Option<u64>>("None Natural", None);
+        assert_serde::<Option<String>>("None Text", None);
+        assert_serde("Some 1", Some(1u64));
+    }
+
+    #[test]
+    fn tuple() {
+        assert_serde::<()>(r#"{=}"#, ());
+        assert_serde::<(u64, String)>(
+            r#"{ _1 = 1, _2 = "foo" }"#,
+            (1, "foo".to_owned()),
+        );
+        assert_serde::<(u64, u64, u64, u64)>(
+            r#"{ _1 = 1, _2 = 2, _3 = 3, _4 = 4 }"#,
+            (1, 2, 3, 4),
+        );
+    }
+
+    #[test]
+    fn structs() {
+        // #[derive(
+        //     Debug, Clone, PartialEq, Eq, Deserialize, Serialize, StaticType,
+        // )]
+        // struct Foo;
+        // assert_serde::<Foo>("{=}", Foo);
+
+        // #[derive(
+        //     Debug, Clone, PartialEq, Eq, Deserialize, Serialize, StaticType,
+        // )]
+        // struct Bar(u64);
+        // assert_serde::<Bar>("{ _1 = 1 }", Bar (1));
+
+        #[derive(
+            Debug, Clone, PartialEq, Eq, Deserialize, Serialize, StaticType,
+        )]
+        struct Baz {
+            x: u64,
+            y: i64,
+        }
+        assert_serde::<Baz>("{ x = 1, y = -2 }", Baz { x: 1, y: -2 });
+    }
+
+    #[test]
+    fn enums() {
+        #[derive(
+            Debug, Clone, PartialEq, Eq, Deserialize, Serialize, StaticType,
+        )]
+        enum Foo {
+            X(u64),
+            Y(i64),
+        }
+        assert_serde::<Foo>("< X: Natural | Y: Integer >.X 1", Foo::X(1));
+
+        #[derive(
+            Debug, Clone, PartialEq, Eq, Deserialize, Serialize, StaticType,
+        )]
+        enum Bar {
+            X,
+            Y(i64),
+        }
+        assert_serde::<Bar>("< X | Y: Integer >.X", Bar::X);
+
+        assert!(from_str("< X | Y: Integer >.Y")
+            .static_type_annotation()
+            .parse::<Bar>()
+            .is_err());
+    }
+}