1 files changed, 237 insertions, 15 deletions

diff --git a/serde_dhall/src/value.rs b/serde_dhall/src/value.rs
index 88727bc..f542f0a 100644
--- a/serde_dhall/src/value.rs
+++ b/serde_dhall/src/value.rs
@@ -1,19 +1,101 @@
-use dhall::semantics::{Hir, Nir};
-use dhall::syntax::Expr;
+use std::collections::{BTreeMap, HashMap};
 
-use crate::simple::{SimpleType, SimpleValue};
-use crate::{Deserialize, Error, Sealed};
+use dhall::semantics::{Hir, HirKind, Nir, NirKind};
+use dhall::syntax::{Builtin, Expr, ExprKind, NumKind, Span};
+
+use crate::{Deserialize, Error, Result, Sealed};
 
 #[doc(hidden)]
 /// An arbitrary Dhall value.
 #[derive(Debug, Clone)]
 pub struct Value {
     /// Invariant: in normal form
-    pub(crate) hir: Hir,
+    hir: Hir,
     /// Cached conversions because they are annoying to construct from Hir.
     /// At most one of them will be `Some`.
-    pub(crate) as_simple_val: Option<SimpleValue>,
-    pub(crate) as_simple_ty: Option<SimpleType>,
+    as_simple_val: Option<SimpleValue>,
+    as_simple_ty: Option<SimpleType>,
+}
+
+/// A simple value of the kind that can be decoded with serde
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub(crate) enum SimpleValue {
+    Num(NumKind),
+    Text(String),
+    Optional(Option<Box<SimpleValue>>),
+    List(Vec<SimpleValue>),
+    Record(BTreeMap<String, SimpleValue>),
+    Union(String, Option<Box<SimpleValue>>),
+}
+
+/// The type of a value that can be decoded by Serde, like `{ x: Bool, y: List Natural }`.
+///
+/// A `SimpleType` is used when deserializing values to ensure they are of the expected type.
+/// Rather than letting `serde` handle potential type mismatches, this uses the type-checking
+/// capabilities of Dhall to catch errors early and cleanly indicate in the user's code where the
+/// mismatch happened.
+///
+/// You would typically not manipulate `SimpleType`s by hand but rather let Rust infer it for your
+/// datatype using the [`StaticType`][TODO] trait, and methods that require it like
+/// [`from_file_static_type`][TODO] and [`Options::static_type_annotation`][TODO]. If you need to supply a
+/// `SimpleType` manually however, you can deserialize it like any other Dhall value using the
+/// functions provided by this crate.
+///
+/// # Examples
+///
+/// ```rust
+/// # fn main() -> serde_dhall::Result<()> {
+/// use std::collections::HashMap;
+/// use serde_dhall::SimpleType;
+///
+/// let ty: SimpleType =
+///     serde_dhall::from_str("{ x: Natural, y: Natural }")?;
+///
+/// let mut map = HashMap::new();
+/// map.insert("x".to_string(), SimpleType::Natural);
+/// map.insert("y".to_string(), SimpleType::Natural);
+/// assert_eq!(ty, SimpleType::Record(map));
+/// # Ok(())
+/// # }
+/// ```
+///
+/// ```rust
+/// # fn main() -> serde_dhall::Result<()> {
+/// use serde_dhall::{SimpleType, StaticType};
+///
+/// #[derive(StaticType)]
+/// struct Foo {
+///     x: bool,
+///     y: Vec<u64>,
+/// }
+///
+/// let ty: SimpleType =
+///     serde_dhall::from_str("{ x: Bool, y: List Natural }")?;
+///
+/// assert_eq!(ty, Foo::static_type());
+/// # Ok(())
+/// # }
+/// ```
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub enum SimpleType {
+    /// Corresponds to the Dhall type `Bool`
+    Bool,
+    /// Corresponds to the Dhall type `Natural`
+    Natural,
+    /// Corresponds to the Dhall type `Integer`
+    Integer,
+    /// Corresponds to the Dhall type `Double`
+    Double,
+    /// Corresponds to the Dhall type `Text`
+    Text,
+    /// Corresponds to the Dhall type `Optional T`
+    Optional(Box<SimpleType>),
+    /// Corresponds to the Dhall type `List T`
+    List(Box<SimpleType>),
+    /// Corresponds to the Dhall type `{ x : T, y : U }`
+    Record(HashMap<String, SimpleType>),
+    /// Corresponds to the Dhall type `< x : T | y : U >`
+    Union(HashMap<String, Option<SimpleType>>),
 }
 
 impl Value {
@@ -25,6 +107,10 @@ impl Value {
         }
     }
 
+    pub(crate) fn as_hir(&self) -> &Hir {
+        &self.hir
+    }
+
     /// Converts a Value into a SimpleValue.
     pub(crate) fn to_simple_value(&self) -> Option<SimpleValue> {
         self.as_simple_val.clone()
@@ -41,22 +127,158 @@ impl Value {
     }
 }
 
-impl Eq for Value {}
-impl PartialEq for Value {
-    fn eq(&self, other: &Self) -> bool {
-        self.hir == other.hir
+impl SimpleValue {
+    pub(crate) fn from_nir(nir: &Nir) -> Option<Self> {
+        Some(match nir.kind() {
+            NirKind::Num(lit) => SimpleValue::Num(lit.clone()),
+            NirKind::TextLit(x) => SimpleValue::Text(
+                x.as_text()
+                    .expect("Normal form should ensure the text is a string"),
+            ),
+            NirKind::EmptyOptionalLit(_) => SimpleValue::Optional(None),
+            NirKind::NEOptionalLit(x) => {
+                SimpleValue::Optional(Some(Box::new(Self::from_nir(x)?)))
+            }
+            NirKind::EmptyListLit(_) => SimpleValue::List(vec![]),
+            NirKind::NEListLit(xs) => SimpleValue::List(
+                xs.iter().map(Self::from_nir).collect::<Option<_>>()?,
+            ),
+            NirKind::RecordLit(kvs) => SimpleValue::Record(
+                kvs.iter()
+                    .map(|(k, v)| Some((k.into(), Self::from_nir(v)?)))
+                    .collect::<Option<_>>()?,
+            ),
+            NirKind::UnionLit(field, x, _) => SimpleValue::Union(
+                field.into(),
+                Some(Box::new(Self::from_nir(x)?)),
+            ),
+            NirKind::UnionConstructor(field, ty)
+                if ty.get(field).map(|f| f.is_some()) == Some(false) =>
+            {
+                SimpleValue::Union(field.into(), None)
+            }
+            _ => return None,
+        })
     }
 }
-impl std::fmt::Display for Value {
-    fn fmt(&self, f: &mut std::fmt::Formatter) -> Result<(), std::fmt::Error> {
-        self.to_expr().fmt(f)
+
+impl SimpleType {
+    pub(crate) fn from_nir(nir: &Nir) -> Option<Self> {
+        Some(match nir.kind() {
+            NirKind::BuiltinType(b) => match b {
+                Builtin::Bool => SimpleType::Bool,
+                Builtin::Natural => SimpleType::Natural,
+                Builtin::Integer => SimpleType::Integer,
+                Builtin::Double => SimpleType::Double,
+                Builtin::Text => SimpleType::Text,
+                _ => unreachable!(),
+            },
+            NirKind::OptionalType(t) => {
+                SimpleType::Optional(Box::new(Self::from_nir(t)?))
+            }
+            NirKind::ListType(t) => {
+                SimpleType::List(Box::new(Self::from_nir(t)?))
+            }
+            NirKind::RecordType(kts) => SimpleType::Record(
+                kts.iter()
+                    .map(|(k, v)| Some((k.into(), Self::from_nir(v)?)))
+                    .collect::<Option<_>>()?,
+            ),
+            NirKind::UnionType(kts) => SimpleType::Union(
+                kts.iter()
+                    .map(|(k, v)| {
+                        Some((
+                            k.into(),
+                            v.as_ref()
+                                .map(|v| Ok(Self::from_nir(v)?))
+                                .transpose()?,
+                        ))
+                    })
+                    .collect::<Option<_>>()?,
+            ),
+            _ => return None,
+        })
+    }
+
+    pub(crate) fn to_value(&self) -> Value {
+        Value {
+            hir: self.to_hir(),
+            as_simple_val: None,
+            as_simple_ty: Some(self.clone()),
+        }
+    }
+    pub(crate) fn to_hir(&self) -> Hir {
+        let hir = |k| Hir::new(HirKind::Expr(k), Span::Artificial);
+        hir(match self {
+            SimpleType::Bool => ExprKind::Builtin(Builtin::Bool),
+            SimpleType::Natural => ExprKind::Builtin(Builtin::Natural),
+            SimpleType::Integer => ExprKind::Builtin(Builtin::Integer),
+            SimpleType::Double => ExprKind::Builtin(Builtin::Double),
+            SimpleType::Text => ExprKind::Builtin(Builtin::Text),
+            SimpleType::Optional(t) => ExprKind::App(
+                hir(ExprKind::Builtin(Builtin::Optional)),
+                t.to_hir(),
+            ),
+            SimpleType::List(t) => {
+                ExprKind::App(hir(ExprKind::Builtin(Builtin::List)), t.to_hir())
+            }
+            SimpleType::Record(kts) => ExprKind::RecordType(
+                kts.into_iter()
+                    .map(|(k, t)| (k.as_str().into(), t.to_hir()))
+                    .collect(),
+            ),
+            SimpleType::Union(kts) => ExprKind::UnionType(
+                kts.into_iter()
+                    .map(|(k, t)| {
+                        (k.as_str().into(), t.as_ref().map(|t| t.to_hir()))
+                    })
+                    .collect(),
+            ),
+        })
     }
 }
 
 impl Sealed for Value {}
+impl Sealed for SimpleValue {}
+impl Sealed for SimpleType {}
 
 impl Deserialize for Value {
-    fn from_dhall(v: &Value) -> Result<Self, Error> {
+    fn from_dhall(v: &Value) -> Result<Self> {
         Ok(v.clone())
     }
 }
+impl Deserialize for SimpleValue {
+    fn from_dhall(v: &Value) -> Result<Self> {
+        v.to_simple_value().ok_or_else(|| {
+            Error::Deserialize(format!(
+                "this cannot be deserialized into a simple type: {}",
+                v
+            ))
+        })
+    }
+}
+impl Deserialize for SimpleType {
+    fn from_dhall(v: &Value) -> Result<Self> {
+        v.to_simple_type().ok_or_else(|| {
+            Error::Deserialize(format!(
+                "this cannot be deserialized into a simple type: {}",
+                v
+            ))
+        })
+    }
+}
+
+impl Eq for Value {}
+impl PartialEq for Value {
+    fn eq(&self, other: &Self) -> bool {
+        self.hir == other.hir
+    }
+}
+impl std::fmt::Display for Value {
+    fn fmt(
+        &self,
+        f: &mut std::fmt::Formatter,
+    ) -> std::result::Result<(), std::fmt::Error> {
+        self.to_expr().fmt(f)
+    }
+}