2 files changed, 62 insertions, 6 deletions

diff --git a/dhall/src/lib.rs b/dhall/src/lib.rs
index 25196ba..60b7a0e 100644
--- a/dhall/src/lib.rs
+++ b/dhall/src/lib.rs
@@ -49,11 +49,18 @@ pub struct Typed {
 }
 
 /// A normalized expression.
-///
-/// Invariant: the contained expression must be in normal form,
 #[derive(Debug, Clone)]
 pub struct Normalized(Nir);
 
+/// A Dhall value.
+#[derive(Debug, Clone)]
+pub struct Value {
+    /// Invariant: in normal form
+    pub(crate) hir: Hir,
+    simple_val: Option<SimpleValue>,
+    simple_ty: Option<SimpleType>,
+}
+
 /// Controls conversion from `Nir` to `Expr`
 #[derive(Copy, Clone, Default)]
 pub(crate) struct ToExprOptions {
@@ -99,8 +106,8 @@ impl Resolved {
     pub fn typecheck(&self) -> Result<Typed, TypeError> {
         Ok(Typed::from_tir(typecheck(&self.0)?))
     }
-    pub fn typecheck_with(self, ty: &Normalized) -> Result<Typed, TypeError> {
-        Ok(Typed::from_tir(typecheck_with(&self.0, ty.to_hir())?))
+    pub(crate) fn typecheck_with(self, ty: &Hir) -> Result<Typed, TypeError> {
+        Ok(Typed::from_tir(typecheck_with(&self.0, ty)?))
     }
     /// Converts a value back to the corresponding AST expression.
     pub fn to_expr(&self) -> ResolvedExpr {
@@ -137,6 +144,13 @@ impl Normalized {
     pub fn encode(&self) -> Result<Vec<u8>, EncodeError> {
         binary::encode(&self.to_expr())
     }
+    pub fn to_value(&self) -> Value {
+        Value {
+            hir: self.to_hir(),
+            simple_val: self.0.to_simple_value(),
+            simple_ty: self.0.to_simple_type(),
+        }
+    }
 
     /// Converts a value back to the corresponding AST expression.
     pub fn to_expr(&self) -> NormalizedExpr {
@@ -200,6 +214,36 @@ impl Normalized {
     }
 }
 
+impl Value {
+    /// Parse a string into a Value, and optionally ensure that the value matches the provided type
+    /// annotation.
+    pub fn from_str_with_annot(
+        s: &str,
+        ty: Option<&Self>,
+    ) -> Result<Self, Error> {
+        let resolved = Parsed::parse_str(s)?.resolve()?;
+        let typed = match ty {
+            None => resolved.typecheck()?,
+            Some(ty) => resolved.typecheck_with(&ty.hir)?,
+        };
+        Ok(typed.normalize().to_value())
+    }
+
+    /// Converts a Value into a SimpleValue.
+    pub fn to_simple_value(&self) -> Option<SimpleValue> {
+        self.simple_val.clone()
+    }
+    /// Converts a Value into a SimpleType.
+    pub fn to_simple_type(&self) -> Option<SimpleType> {
+        self.simple_ty.clone()
+    }
+
+    /// Converts a value back to the corresponding AST expression.
+    pub(crate) fn to_expr(&self) -> NormalizedExpr {
+        self.hir.to_expr(ToExprOptions::default())
+    }
+}
+
 macro_rules! derive_traits_for_wrapper_struct {
     ($ty:ident) => {
         impl std::cmp::PartialEq for $ty {
@@ -274,3 +318,15 @@ impl Display for Normalized {
         self.to_expr().fmt(f)
     }
 }
+
+impl Eq for Value {}
+impl PartialEq for Value {
+    fn eq(&self, other: &Self) -> bool {
+        self.hir == other.hir
+    }
+}
+impl Display for Value {
+    fn fmt(&self, f: &mut std::fmt::Formatter) -> Result<(), std::fmt::Error> {
+        self.to_expr().fmt(f)
+    }
+}
diff --git a/dhall/src/semantics/tck/typecheck.rs b/dhall/src/semantics/tck/typecheck.rs
index 173b76d..9fa33f2 100644
--- a/dhall/src/semantics/tck/typecheck.rs
+++ b/dhall/src/semantics/tck/typecheck.rs
@@ -808,8 +808,8 @@ pub(crate) fn typecheck<'hir>(hir: &'hir Hir) -> Result<Tir<'hir>, TypeError> {
 /// Like `typecheck`, but additionally checks that the expression's type matches the provided type.
 pub(crate) fn typecheck_with<'hir>(
     hir: &'hir Hir,
-    ty: Hir,
+    ty: &Hir,
 ) -> Result<Tir<'hir>, TypeError> {
-    let ty = typecheck(&ty)?.eval_to_type(&TyEnv::new())?;
+    let ty = typecheck(ty)?.eval_to_type(&TyEnv::new())?;
     type_with(&TyEnv::new(), hir, Some(ty))
 }