Add a new Deserialize trait for reading dhall values

2 files changed, 64 insertions, 0 deletions

diff --git a/dhall/src/lib.rs b/dhall/src/lib.rs
index 3bfc46f..b49d1c1 100644
--- a/dhall/src/lib.rs
+++ b/dhall/src/lib.rs
@@ -21,7 +21,21 @@ mod imports;
 mod normalize;
 mod traits;
 mod typecheck;
+pub use crate::traits::Deserialize;
 pub use crate::traits::SimpleStaticType;
 pub use crate::traits::StaticType;
 pub use dhall_generator::SimpleStaticType;
 pub mod expr;
+
+pub fn from_str<'a, T: Deserialize<'a>>(
+    s: &'a str,
+    ty: Option<&crate::expr::Type>,
+) -> crate::traits::Result<T> {
+    T::from_str(s, ty)
+}
+
+pub fn from_str_auto_type<'a, T: Deserialize<'a> + StaticType>(
+    s: &'a str,
+) -> crate::traits::Result<T> {
+    from_str(s, Some(&<T as StaticType>::get_static_type()))
+}
diff --git a/dhall/src/traits.rs b/dhall/src/traits.rs
index 4925457..370632e 100644
--- a/dhall/src/traits.rs
+++ b/dhall/src/traits.rs
@@ -19,6 +19,56 @@ pub trait SimpleStaticType {
     fn get_simple_static_type() -> SimpleType;
 }
 
+pub type Error = ();
+pub type Result<T> = std::result::Result<T, Error>;
+
+pub trait Deserialize<'a>: Sized {
+    fn from_str(s: &'a str, ty: Option<&Type>) -> Result<Self>;
+}
+
+impl<'a> Deserialize<'a> for Parsed {
+    /// Simply parses the provided string. Ignores the
+    /// provided type.
+    fn from_str(s: &'a str, _ty: Option<&Type>) -> Result<Self> {
+        Ok(Parsed::parse_str(s).map_err(|_| ())?)
+    }
+}
+
+impl<'a> Deserialize<'a> for Resolved {
+    /// Parses and resolves the provided string. Ignores the
+    /// provided type.
+    fn from_str(s: &'a str, ty: Option<&Type>) -> Result<Self> {
+        Ok(Parsed::from_str(s, ty)?
+            .resolve()
+            .map_err(|_| ())?
+        )
+    }
+}
+
+impl<'a> Deserialize<'a> for Typed {
+    /// Parses, resolves and typechecks the provided string.
+    fn from_str(s: &'a str, ty: Option<&Type>) -> Result<Self> {
+        // TODO: compare with provided type
+        Ok(Resolved::from_str(s, ty)?
+            .typecheck()
+            .map_err(|_| ())?
+        )
+    }
+}
+
+impl<'a> Deserialize<'a> for Normalized {
+    /// Parses, resolves, typechecks and normalizes the provided string.
+    fn from_str(s: &'a str, ty: Option<&Type>) -> Result<Self> {
+        Ok(Typed::from_str(s, ty)?.normalize())
+    }
+}
+
+impl<'a> Deserialize<'a> for Type {
+    fn from_str(s: &'a str, ty: Option<&Type>) -> Result<Self> {
+        Ok(Normalized::from_str(s, ty)?.into_type())
+    }
+}
+
 fn mktype(x: SubExpr<X, X>) -> SimpleType {
     SimpleType(x)
 }