Add basic deserialization support

Closes #13

1 files changed, 64 insertions, 4 deletions

diff --git a/dhall/src/serde.rs b/dhall/src/serde.rs
index 4ac4f3d..196bda1 100644
--- a/dhall/src/serde.rs
+++ b/dhall/src/serde.rs
@@ -1,9 +1,69 @@
-use crate::error::Result;
-use crate::expr::Type;
+use crate::error::{Error, Result};
+use crate::expr::{Normalized, Type};
 use crate::traits::Deserialize;
+use dhall_core::*;
+use std::borrow::Cow;
 
 impl<'a, T: serde::Deserialize<'a>> Deserialize<'a> for T {
-    fn from_str(_s: &'a str, _ty: Option<&Type>) -> Result<Self> {
-        unimplemented!()
+    fn from_str(s: &'a str, ty: Option<&Type>) -> Result<Self> {
+        let expr = Normalized::from_str(s, ty)?;
+        T::deserialize(Deserializer(Cow::Owned(expr.0)))
+    }
+}
+
+struct Deserializer<'a>(Cow<'a, SubExpr<X, X>>);
+
+impl serde::de::Error for Error {
+    fn custom<T>(msg: T) -> Self
+    where
+        T: std::fmt::Display,
+    {
+        Error::Deserialize(msg.to_string())
+    }
+}
+
+impl<'de: 'a, 'a> serde::de::IntoDeserializer<'de, Error> for Deserializer<'a> {
+    type Deserializer = Deserializer<'a>;
+    fn into_deserializer(self) -> Self::Deserializer {
+        self
+    }
+}
+
+impl<'de: 'a, 'a> serde::Deserializer<'de> for Deserializer<'a> {
+    type Error = Error;
+    fn deserialize_any<V>(self, visitor: V) -> Result<V::Value>
+    where
+        V: serde::de::Visitor<'de>,
+    {
+        use std::convert::TryInto;
+        use ExprF::*;
+        match self.0.as_ref().as_ref() {
+            NaturalLit(n) => match (*n).try_into() {
+                Ok(n64) => visitor.visit_u64(n64),
+                Err(_) => match (*n).try_into() {
+                    Ok(n32) => visitor.visit_u32(n32),
+                    Err(_) => unimplemented!(),
+                },
+            },
+            IntegerLit(n) => match (*n).try_into() {
+                Ok(n64) => visitor.visit_i64(n64),
+                Err(_) => match (*n).try_into() {
+                    Ok(n32) => visitor.visit_i32(n32),
+                    Err(_) => unimplemented!(),
+                },
+            },
+            RecordLit(m) => visitor.visit_map(
+                serde::de::value::MapDeserializer::new(m.iter().map(
+                    |(k, v)| (k.as_ref(), Deserializer(Cow::Borrowed(v))),
+                )),
+            ),
+            _ => unimplemented!(),
+        }
+    }
+
+    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 tuple
+        tuple_struct map struct enum identifier ignored_any
     }
 }