Merge branch 'serde'

13 files changed, 569 insertions, 262 deletions

diff --git a/dhall/src/error.rs b/dhall/src/error.rs
new file mode 100644
index 0000000..cfd6f09
--- /dev/null
+++ b/dhall/src/error.rs
@@ -0,0 +1,32 @@
+use quick_error::quick_error;
+
+pub type Result<T> = std::result::Result<T, Error>;
+
+quick_error! {
+    #[derive(Debug)]
+    pub enum Error {
+        IO(err: std::io::Error) {
+            from()
+            display("{}", err)
+        }
+        Parse(err: dhall_core::ParseError) {
+            from()
+            display("{}", err)
+        }
+        Decode(err: crate::binary::DecodeError) {
+            from()
+            display("{:?}", err)
+        }
+        Resolve(err: crate::imports::ImportError) {
+            from()
+            display("{}", err)
+        }
+        Typecheck(err: crate::typecheck::TypeError<dhall_core::X>) {
+            from()
+            display("{:?}", err)
+        }
+        Deserialize(err: String) {
+            display("{}", err)
+        }
+    }
+}
diff --git a/dhall/src/expr.rs b/dhall/src/expr.rs
index 7baf628..5ff097b 100644
--- a/dhall/src/expr.rs
+++ b/dhall/src/expr.rs
@@ -36,6 +36,11 @@ derive_other_traits!(Typed);
 pub struct Normalized(pub(crate) SubExpr<X, X>, pub(crate) Type);
 derive_other_traits!(Normalized);
 
+/// An expression of type `Type` (like `Bool` or `Natural -> Text`, but not `Type`)
+#[derive(Debug, Clone, Eq)]
+pub struct SimpleType(pub(crate) SubExpr<X, X>);
+derive_other_traits!(SimpleType);
+
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub struct Type(pub(crate) TypeInternal);
 
@@ -44,3 +49,19 @@ pub(crate) enum TypeInternal {
     Expr(Box<Normalized>),
     Untyped,
 }
+
+// Exposed for the macros
+#[doc(hidden)]
+impl From<SimpleType> for SubExpr<X, X> {
+    fn from(x: SimpleType) -> SubExpr<X, X> {
+        x.0
+    }
+}
+
+// Exposed for the macros
+#[doc(hidden)]
+impl From<SubExpr<X, X>> for SimpleType {
+    fn from(x: SubExpr<X, X>) -> SimpleType {
+        SimpleType(x)
+    }
+}
diff --git a/dhall/src/imports.rs b/dhall/src/imports.rs
index fdde8c3..7810c55 100644
--- a/dhall/src/imports.rs
+++ b/dhall/src/imports.rs
@@ -1,46 +1,17 @@
-// use dhall_core::{Expr, FilePrefix, Import, ImportLocation, ImportMode, X};
-use dhall_core::{Expr, Import, X};
-// use std::path::Path;
-use crate::binary::DecodeError;
+use crate::error::Error;
 use crate::expr::*;
 use dhall_core::*;
-use std::fmt;
+use quick_error::quick_error;
 use std::fs::File;
 use std::io::Read;
 use std::path::Path;
 use std::path::PathBuf;
 
-#[derive(Debug)]
-pub enum ImportError {
-    ParseError(ParseError),
-    BinaryDecodeError(DecodeError),
-    IOError(std::io::Error),
-    UnexpectedImportError(Import),
-}
-impl From<ParseError> for ImportError {
-    fn from(e: ParseError) -> Self {
-        ImportError::ParseError(e)
-    }
-}
-impl From<DecodeError> for ImportError {
-    fn from(e: DecodeError) -> Self {
-        ImportError::BinaryDecodeError(e)
-    }
-}
-impl From<std::io::Error> for ImportError {
-    fn from(e: std::io::Error) -> Self {
-        ImportError::IOError(e)
-    }
-}
-impl fmt::Display for ImportError {
-    fn fmt(&self, f: &mut fmt::Formatter) -> Result<(), fmt::Error> {
-        use self::ImportError::*;
-        match self {
-            ParseError(e) => e.fmt(f),
-            BinaryDecodeError(_) => unimplemented!(),
-            IOError(e) => e.fmt(f),
-            UnexpectedImportError(e) => e.fmt(f),
-        }
+quick_error! {
+    #[derive(Debug)]
+    pub enum ImportError {
+        Recursive(import: Import, err: Box<Error>) {}
+        UnexpectedImport(import: Import) {}
     }
 }
 
@@ -53,7 +24,7 @@ pub enum ImportRoot {
 fn resolve_import(
     import: &Import,
     root: &ImportRoot,
-) -> Result<Expr<X, X>, ImportError> {
+) -> Result<Resolved, ImportError> {
     use self::ImportRoot::*;
     use dhall_core::FilePrefix::*;
     use dhall_core::ImportLocation::*;
@@ -63,16 +34,23 @@ fn resolve_import(
     match &import.location_hashed.location {
         Local(prefix, path) => {
             let path = match prefix {
+                // TODO: fail gracefully
                 Parent => cwd.parent().unwrap().join(path),
                 Here => cwd.join(path),
                 _ => unimplemented!("{:?}", import),
             };
-            load_dhall_file(&path, true)
+            Ok(load_import(&path).map_err(|e| {
+                ImportError::Recursive(import.clone(), Box::new(e))
+            })?)
         }
         _ => unimplemented!("{:?}", import),
     }
 }
 
+fn load_import(f: &Path) -> Result<Resolved, Error> {
+    Ok(Parsed::parse_file(f)?.resolve()?)
+}
+
 fn resolve_expr(
     Parsed(expr, root): Parsed,
     allow_imports: bool,
@@ -80,9 +58,9 @@ fn resolve_expr(
     let resolve = |import: &Import| -> Result<SubExpr<X, X>, ImportError> {
         if allow_imports {
             let expr = resolve_import(import, &root)?;
-            Ok(expr.roll())
+            Ok(expr.0)
         } else {
-            Err(ImportError::UnexpectedImportError(import.clone()))
+            Err(ImportError::UnexpectedImport(import.clone()))
         }
     };
     let expr = expr.as_ref().traverse_embed(&resolve)?;
@@ -90,7 +68,7 @@ fn resolve_expr(
 }
 
 impl Parsed {
-    pub fn load_from_file(f: &Path) -> Result<Parsed, ImportError> {
+    pub fn parse_file(f: &Path) -> Result<Parsed, Error> {
         let mut buffer = String::new();
         File::open(f)?.read_to_string(&mut buffer)?;
         let expr = parse_expr(&*buffer)?;
@@ -98,13 +76,13 @@ impl Parsed {
         Ok(Parsed(expr, root))
     }
 
-    pub fn load_from_str(s: &str) -> Result<Parsed, ImportError> {
+    pub fn parse_str(s: &str) -> Result<Parsed, Error> {
         let expr = parse_expr(s)?;
         let root = ImportRoot::LocalDir(std::env::current_dir()?);
         Ok(Parsed(expr, root))
     }
 
-    pub fn load_from_binary_file(f: &Path) -> Result<Parsed, ImportError> {
+    pub fn parse_binary_file(f: &Path) -> Result<Parsed, Error> {
         let mut buffer = Vec::new();
         File::open(f)?.read_to_end(&mut buffer)?;
         let expr = crate::binary::decode(&buffer)?;
@@ -119,13 +97,3 @@ impl Parsed {
         crate::imports::resolve_expr(self, false)
     }
 }
-
-// Deprecated
-pub fn load_dhall_file(
-    f: &Path,
-    resolve_imports: bool,
-) -> Result<Expr<X, X>, ImportError> {
-    let expr = Parsed::load_from_file(f)?;
-    let expr = resolve_expr(expr, resolve_imports)?;
-    Ok(expr.0.unroll())
-}
diff --git a/dhall/src/lib.rs b/dhall/src/lib.rs
index 5c5a641..8af5af9 100644
--- a/dhall/src/lib.rs
+++ b/dhall/src/lib.rs
@@ -9,6 +9,111 @@
     clippy::many_single_char_names
 )]
 
+//! [Dhall][dhall] is a programmable configuration language that provides a non-repetitive
+//! alternative to JSON and YAML.
+//!
+//! You can think of Dhall as: JSON/YAML + types + imports + functions
+//!
+//! For a description of the dhall language, examples, tutorials, and more, see the [language
+//! website][dhall].
+//!
+//! This crate provides support for consuming dhall files the same way you would consume JSON or
+//! YAML. It uses the [Serde][serde] serialization library to provide drop-in support for dhall
+//! for any datatype that supports serde (and that's a lot of them !).
+//!
+//! This library is limited to deserializing (reading) dhall values; serializing (writing)
+//! values to dhall is not supported for now.
+//!
+//! # Examples
+//!
+//! ### Custom datatype
+//!
+//! If you have a custom datatype for which you derived [serde::Deserialize], chances are
+//! you will be able to derive [SimpleStaticType] for it as well. This gives you access to
+//! a dhall representation of your datatype that can be outputted to users, and
+//! allows easy type-safe deserializing.
+//!
+//! ```edition2018
+//! use serde::Deserialize;
+//! use dhall::SimpleStaticType;
+//!
+//! #[derive(Debug, Deserialize, SimpleStaticType)]
+//! struct Point {
+//!     x: u64,
+//!     y: u64,
+//! }
+//!
+//! fn main() {
+//!     // Some dhall data
+//!     let data = "{ x = 1, y = 1 + 1 }";
+//!
+//!     // Convert the dhall string to a Point.
+//!     let point: Point =
+//!             dhall::from_str_auto_type(&data)
+//!                 .expect("An error ocurred !");
+//!
+//!     // Prints "point = Point { x: 1, y: 2 }"
+//!     println!("point = {:?}", point);
+//! }
+//! ```
+//!
+//! ### Loosely typed
+//!
+//! If you used to consume JSON or YAML in a loosely typed way, you can continue to do so
+//! with dhall. You only need to replace [serde_json::from_str] or [serde_yaml::from_str]
+//! with [dhall::from_str][from_str].
+//! More generally, if the [SimpleStaticType] derive doesn't suit your needs, you can still
+//! deserialize any valid dhall file that serde can handle.
+//!
+//! [serde_json::from_str]: https://docs.serde.rs/serde_json/de/fn.from_str.html
+//! [serde_yaml::from_str]: https://docs.serde.rs/serde_yaml/fn.from_str.html
+//!
+//! ```edition2018
+//! use std::collections::BTreeMap;
+//!
+//! let mut map = BTreeMap::new();
+//! map.insert("x".to_string(), 1);
+//! map.insert("y".to_string(), 2);
+//!
+//! // Some dhall data
+//! let data = "{ x = 1, y = 1 + 1 } : { x: Natural, y: Natural }";
+//!
+//! // Deserialize it to a Rust type.
+//! let deserialized_map: BTreeMap<String, usize> =
+//!         dhall::from_str(&data, None)
+//!             .expect("Failed reading the data !");
+//! assert_eq!(map, deserialized_map);
+//! ```
+//!
+//! You can of course specify a dhall type that the input should match.
+//!
+//! ```edition2018
+//! use std::collections::BTreeMap;
+//!
+//! let mut map = BTreeMap::new();
+//! map.insert("x".to_string(), 1);
+//! map.insert("y".to_string(), 2);
+//!
+//! // Some dhall data
+//! let point_data = "{ x = 1, y = 1 + 1 }";
+//! let point_type_data = "{ x: Natural, y: Natural }";
+//!
+//! // Construct a type
+//! let point_type =
+//!         dhall::from_str(point_type_data, None)
+//!             .expect("Could not parse the Point type");
+//!
+//! // Deserialize it to a Rust type.
+//! let deserialized_map: BTreeMap<String, usize> =
+//!         dhall::from_str(&point_data, Some(&point_type))
+//!             .expect("Failed reading the data !");
+//! assert_eq!(map, deserialized_map);
+//! ```
+//!
+//! [dhall]: https://dhall-lang.org/
+//! [serde]: https://docs.serde.rs/serde/
+//! [serde::Deserialize]: https://docs.serde.rs/serde/trait.Deserialize.html
+
 #[cfg(test)]
 #[macro_use]
 mod tests;
@@ -21,6 +126,23 @@ 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::StaticType;
+pub use dhall_generator::SimpleStaticType;
+pub mod error;
 pub mod expr;
+pub mod serde;
+
+pub fn from_str<'a, T: Deserialize<'a>>(
+    s: &'a str,
+    ty: Option<&crate::expr::Type>,
+) -> crate::error::Result<T> {
+    T::from_str(s, ty)
+}
+
+pub fn from_str_auto_type<'a, T: Deserialize<'a> + StaticType>(
+    s: &'a str,
+) -> crate::error::Result<T> {
+    from_str(s, Some(&<T as StaticType>::get_static_type()))
+}
diff --git a/dhall/src/main.rs b/dhall/src/main.rs
index 2881d5a..3b61a44 100644
--- a/dhall/src/main.rs
+++ b/dhall/src/main.rs
@@ -55,7 +55,7 @@ fn main() {
     let mut buffer = String::new();
     io::stdin().read_to_string(&mut buffer).unwrap();
 
-    let expr = match dhall::expr::Parsed::load_from_str(&buffer) {
+    let expr = match dhall::expr::Parsed::parse_str(&buffer) {
         Ok(expr) => expr,
         Err(e) => {
             print_error(&format!("Parse error {}", e), &buffer, 0, 0);
diff --git a/dhall/src/normalize.rs b/dhall/src/normalize.rs
index d7f1848..608e6ee 100644
--- a/dhall/src/normalize.rs
+++ b/dhall/src/normalize.rs
@@ -337,7 +337,7 @@ mod spec_tests {
 
     macro_rules! norm {
         ($name:ident, $path:expr) => {
-            make_spec_test!(Normalization, $name, $path);
+            make_spec_test!(Normalization, Success, $name, $path);
         };
     }
 
diff --git a/dhall/src/serde.rs b/dhall/src/serde.rs
new file mode 100644
index 0000000..196bda1
--- /dev/null
+++ b/dhall/src/serde.rs
@@ -0,0 +1,69 @@
+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> {
+        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
+    }
+}
diff --git a/dhall/src/tests.rs b/dhall/src/tests.rs
index ebb8855..23ec1f4 100644
--- a/dhall/src/tests.rs
+++ b/dhall/src/tests.rs
@@ -19,160 +19,134 @@ right: `{}`"#,
 
 #[macro_export]
 macro_rules! make_spec_test {
-    ($type:ident, $name:ident, $path:expr) => {
+    ($type:ident, $status:ident, $name:ident, $path:expr) => {
         #[test]
         #[allow(non_snake_case)]
         fn $name() {
             use crate::tests::*;
-            run_test($path, Feature::$type);
+            // Many tests stack overflow in debug mode
+            std::thread::Builder::new()
+                .stack_size(4 * 1024 * 1024)
+                .spawn(|| {
+                    run_test($path, Feature::$type, Status::$status)
+                        .map_err(|e| println!("{}", e))
+                        .unwrap();
+                })
+                .unwrap()
+                .join()
+                .unwrap();
         }
     };
 }
 
-use crate::imports::ImportError;
-use crate::*;
-use dhall_core::*;
-use dhall_generator as dhall;
+use crate::error::{Error, Result};
+use crate::expr::Parsed;
 use std::path::PathBuf;
 
-#[allow(dead_code)]
+#[derive(Copy, Clone)]
 pub enum Feature {
-    ParserSuccess,
-    ParserFailure,
+    Parser,
     Normalization,
-    TypecheckSuccess,
-    TypecheckFailure,
-    TypeInferenceSuccess,
-    TypeInferenceFailure,
+    Typecheck,
+    TypeInference,
 }
 
-// Deprecated
-fn read_dhall_file<'i>(file_path: &str) -> Result<Expr<X, X>, ImportError> {
-    crate::imports::load_dhall_file(&PathBuf::from(file_path), true)
+#[derive(Copy, Clone)]
+pub enum Status {
+    Success,
+    Failure,
 }
 
-fn load_from_file_str<'i>(
-    file_path: &str,
-) -> Result<crate::expr::Parsed, ImportError> {
-    crate::expr::Parsed::load_from_file(&PathBuf::from(file_path))
+fn parse_file_str<'i>(file_path: &str) -> Result<Parsed> {
+    Parsed::parse_file(&PathBuf::from(file_path))
 }
 
-fn load_from_binary_file_str<'i>(
-    file_path: &str,
-) -> Result<crate::expr::Parsed, ImportError> {
-    crate::expr::Parsed::load_from_binary_file(&PathBuf::from(file_path))
+fn parse_binary_file_str<'i>(file_path: &str) -> Result<Parsed> {
+    Parsed::parse_binary_file(&PathBuf::from(file_path))
 }
 
-pub fn run_test(base_path: &str, feature: Feature) {
+pub fn run_test(
+    base_path: &str,
+    feature: Feature,
+    status: Status,
+) -> Result<()> {
     use self::Feature::*;
-    let base_path_prefix = match feature {
-        ParserSuccess => "parser/success/",
-        ParserFailure => "parser/failure/",
-        Normalization => "normalization/success/",
-        TypecheckSuccess => "typecheck/success/",
-        TypecheckFailure => "typecheck/failure/",
-        TypeInferenceSuccess => "type-inference/success/",
-        TypeInferenceFailure => "type-inference/failure/",
+    use self::Status::*;
+    let feature_prefix = match feature {
+        Parser => "parser/",
+        Normalization => "normalization/",
+        Typecheck => "typecheck/",
+        TypeInference => "type-inference/",
+    };
+    let status_prefix = match status {
+        Success => "success/",
+        Failure => "failure/",
     };
-    let base_path =
-        "../dhall-lang/tests/".to_owned() + base_path_prefix + base_path;
-    match feature {
-        ParserSuccess => {
+    let base_path = "../dhall-lang/tests/".to_owned()
+        + feature_prefix
+        + status_prefix
+        + base_path;
+    match status {
+        Success => {
             let expr_file_path = base_path.clone() + "A.dhall";
-            let expected_file_path = base_path + "B.dhallb";
-            let expr = load_from_file_str(&expr_file_path)
-                .map_err(|e| println!("{}", e))
-                .unwrap();
+            let expr = parse_file_str(&expr_file_path)?;
 
-            let expected = load_from_binary_file_str(&expected_file_path)
-                .map_err(|e| println!("{}", e))
-                .unwrap();
+            if let Parser = feature {
+                let expected_file_path = base_path + "B.dhallb";
+                let expected = parse_binary_file_str(&expected_file_path)?;
 
-            assert_eq_pretty!(expr, expected);
+                assert_eq_pretty!(expr, expected);
 
-            // Round-trip pretty-printer
-            let expr =
-                crate::expr::Parsed::load_from_str(&expr.to_string()).unwrap();
-            assert_eq!(expr, expected);
-        }
-        ParserFailure => {
-            let file_path = base_path + ".dhall";
-            let err = load_from_file_str(&file_path).unwrap_err();
-            match err {
-                ImportError::ParseError(_) => {}
-                e => panic!("Expected parse error, got: {:?}", e),
+                // Round-trip pretty-printer
+                let expr: Parsed = crate::from_str(&expr.to_string(), None)?;
+                assert_eq!(expr, expected);
+
+                return Ok(());
             }
-        }
-        Normalization => {
-            let expr_file_path = base_path.clone() + "A.dhall";
+
+            let expr = expr.resolve()?;
+
             let expected_file_path = base_path + "B.dhall";
-            let expr = load_from_file_str(&expr_file_path)
-                .unwrap()
-                .resolve()
-                .unwrap()
-                .skip_typecheck()
-                .normalize();
-            let expected = load_from_file_str(&expected_file_path)
-                .unwrap()
-                .resolve()
-                .unwrap()
+            let expected = parse_file_str(&expected_file_path)?
+                .resolve()?
                 .skip_typecheck()
-                .normalize();
+                .skip_normalize();
 
-            assert_eq_display!(expr, expected);
-        }
-        TypecheckFailure => {
-            let file_path = base_path + ".dhall";
-            load_from_file_str(&file_path)
-                .unwrap()
-                .skip_resolve()
-                .unwrap()
-                .typecheck()
-                .unwrap_err();
-        }
-        TypecheckSuccess => {
-            // Many tests stack overflow in debug mode
-            std::thread::Builder::new()
-                .stack_size(4 * 1024 * 1024)
-                .spawn(|| {
-                    let expr_file_path = base_path.clone() + "A.dhall";
-                    let expected_file_path = base_path + "B.dhall";
-                    let expr = rc(read_dhall_file(&expr_file_path).unwrap());
-                    let expected =
-                        rc(read_dhall_file(&expected_file_path).unwrap());
-                    typecheck::type_of(dhall::subexpr!(expr: expected))
-                        .unwrap();
-                })
-                .unwrap()
-                .join()
-                .unwrap();
+            match feature {
+                Parser => unreachable!(),
+                Typecheck => {
+                    expr.typecheck_with(&expected.into_type())?;
+                }
+                TypeInference => {
+                    let expr = expr.typecheck()?;
+                    let ty = expr.get_type().as_normalized()?;
+                    assert_eq_display!(ty, &expected);
+                }
+                Normalization => {
+                    let expr = expr.skip_typecheck().normalize();
+                    assert_eq_display!(expr, expected);
+                }
+            }
         }
-        TypeInferenceFailure => {
+        Failure => {
             let file_path = base_path + ".dhall";
-            load_from_file_str(&file_path)
-                .unwrap()
-                .skip_resolve()
-                .unwrap()
-                .typecheck()
-                .unwrap_err();
-        }
-        TypeInferenceSuccess => {
-            let expr_file_path = base_path.clone() + "A.dhall";
-            let expected_file_path = base_path + "B.dhall";
-            let expr = load_from_file_str(&expr_file_path)
-                .unwrap()
-                .skip_resolve()
-                .unwrap()
-                .typecheck()
-                .unwrap();
-            let ty = expr.get_type().as_normalized().unwrap();
-            let expected = load_from_file_str(&expected_file_path)
-                .unwrap()
-                .skip_resolve()
-                .unwrap()
-                .skip_typecheck()
-                .skip_normalize();
-            assert_eq_display!(ty, &expected);
+            match feature {
+                Parser => {
+                    let err = parse_file_str(&file_path).unwrap_err();
+                    match err {
+                        Error::Parse(_) => {}
+                        e => panic!("Expected parse error, got: {:?}", e),
+                    }
+                }
+                Normalization => unreachable!(),
+                Typecheck | TypeInference => {
+                    parse_file_str(&file_path)?
+                        .skip_resolve()?
+                        .typecheck()
+                        .unwrap_err();
+                }
+            }
         }
     }
+    Ok(())
 }
diff --git a/dhall/src/traits.rs b/dhall/src/traits.rs
deleted file mode 100644
index 64e07d9..0000000
--- a/dhall/src/traits.rs
+++ /dev/null
@@ -1,77 +0,0 @@
-use dhall_core::*;
-use dhall_generator::*;
-
-#[derive(Debug, Clone)]
-pub enum ConversionError {}
-
-pub trait StaticType {
-    fn get_type() -> DhallExpr;
-    // fn as_dhall(&self) -> DhallExpr;
-    // fn from_dhall(e: DhallExpr) -> Result<Self, DhallConversionError>;
-}
-
-impl StaticType for bool {
-    fn get_type() -> DhallExpr {
-        dhall_expr!(Bool)
-    }
-}
-
-impl StaticType for Natural {
-    fn get_type() -> DhallExpr {
-        dhall_expr!(Natural)
-    }
-}
-
-impl StaticType for Integer {
-    fn get_type() -> DhallExpr {
-        dhall_expr!(Integer)
-    }
-}
-
-impl StaticType for String {
-    fn get_type() -> DhallExpr {
-        dhall_expr!(Text)
-    }
-}
-
-impl<A: StaticType, B: StaticType> StaticType for (A, B) {
-    fn get_type() -> DhallExpr {
-        let ta = A::get_type();
-        let tb = B::get_type();
-        dhall_expr!({ _1: ta, _2: tb })
-    }
-}
-
-impl<T: StaticType> StaticType for Option<T> {
-    fn get_type() -> DhallExpr {
-        let t = T::get_type();
-        dhall_expr!(Optional t)
-    }
-}
-
-impl<T: StaticType> StaticType for Vec<T> {
-    fn get_type() -> DhallExpr {
-        let t = T::get_type();
-        dhall_expr!(List t)
-    }
-}
-
-impl<'a, T: StaticType> StaticType for &'a T {
-    fn get_type() -> DhallExpr {
-        T::get_type()
-    }
-}
-
-impl<T> StaticType for std::marker::PhantomData<T> {
-    fn get_type() -> DhallExpr {
-        dhall_expr!({})
-    }
-}
-
-impl<T: StaticType, E: StaticType> StaticType for Result<T, E> {
-    fn get_type() -> DhallExpr {
-        let tt = T::get_type();
-        let te = E::get_type();
-        dhall_expr!(< Ok: tt | Err: te>)
-    }
-}
diff --git a/dhall/src/traits/deserialize.rs b/dhall/src/traits/deserialize.rs
new file mode 100644
index 0000000..1fbdfe1
--- /dev/null
+++ b/dhall/src/traits/deserialize.rs
@@ -0,0 +1,46 @@
+use crate::error::*;
+use crate::expr::*;
+
+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, _: Option<&Type>) -> Result<Self> {
+        Ok(Parsed::parse_str(s)?)
+    }
+}
+
+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()?)
+    }
+}
+
+impl<'a> Deserialize<'a> for Typed {
+    /// Parses, resolves and typechecks the provided string.
+    fn from_str(s: &'a str, ty: Option<&Type>) -> Result<Self> {
+        let resolved = Resolved::from_str(s, ty)?;
+        match ty {
+            None => Ok(resolved.typecheck()?),
+            Some(t) => Ok(resolved.typecheck_with(t)?),
+        }
+    }
+}
+
+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())
+    }
+}
diff --git a/dhall/src/traits/mod.rs b/dhall/src/traits/mod.rs
new file mode 100644
index 0000000..4ce8f97
--- /dev/null
+++ b/dhall/src/traits/mod.rs
@@ -0,0 +1,4 @@
+mod deserialize;
+mod static_type;
+pub use deserialize::Deserialize;
+pub use static_type::{SimpleStaticType, StaticType};
diff --git a/dhall/src/traits/static_type.rs b/dhall/src/traits/static_type.rs
new file mode 100644
index 0000000..6c41e3f
--- /dev/null
+++ b/dhall/src/traits/static_type.rs
@@ -0,0 +1,128 @@
+use crate::expr::*;
+use dhall_core::*;
+use dhall_generator::*;
+
+pub trait StaticType {
+    fn get_static_type() -> Type;
+}
+
+/// Trait for rust types that can be represented in dhall in
+/// a single way, independent of the value. A typical example is `Option<bool>`,
+/// represented by the dhall expression `Optional Bool`. A typical counterexample
+/// is `HashMap<Text, bool>` because dhall cannot represent records with a
+/// variable number of fields.
+pub trait SimpleStaticType {
+    fn get_simple_static_type() -> SimpleType;
+}
+
+fn mktype(x: SubExpr<X, X>) -> SimpleType {
+    SimpleType(x)
+}
+
+impl<T: SimpleStaticType> StaticType for T {
+    fn get_static_type() -> Type {
+        crate::expr::Normalized(
+            T::get_simple_static_type().into(),
+            Type::const_type(),
+        )
+        .into_type()
+    }
+}
+
+impl StaticType for SimpleType {
+    fn get_static_type() -> Type {
+        Type::const_type()
+    }
+}
+
+impl SimpleStaticType for bool {
+    fn get_simple_static_type() -> SimpleType {
+        mktype(dhall_expr!(Bool))
+    }
+}
+
+impl SimpleStaticType for Natural {
+    fn get_simple_static_type() -> SimpleType {
+        mktype(dhall_expr!(Natural))
+    }
+}
+
+impl SimpleStaticType for u32 {
+    fn get_simple_static_type() -> SimpleType {
+        mktype(dhall_expr!(Natural))
+    }
+}
+
+impl SimpleStaticType for u64 {
+    fn get_simple_static_type() -> SimpleType {
+        mktype(dhall_expr!(Natural))
+    }
+}
+
+impl SimpleStaticType for Integer {
+    fn get_simple_static_type() -> SimpleType {
+        mktype(dhall_expr!(Integer))
+    }
+}
+
+impl SimpleStaticType for i32 {
+    fn get_simple_static_type() -> SimpleType {
+        mktype(dhall_expr!(Integer))
+    }
+}
+
+impl SimpleStaticType for i64 {
+    fn get_simple_static_type() -> SimpleType {
+        mktype(dhall_expr!(Integer))
+    }
+}
+
+impl SimpleStaticType for String {
+    fn get_simple_static_type() -> SimpleType {
+        mktype(dhall_expr!(Text))
+    }
+}
+
+impl<A: SimpleStaticType, B: SimpleStaticType> SimpleStaticType for (A, B) {
+    fn get_simple_static_type() -> SimpleType {
+        let ta: SubExpr<_, _> = A::get_simple_static_type().into();
+        let tb: SubExpr<_, _> = B::get_simple_static_type().into();
+        mktype(dhall_expr!({ _1: ta, _2: tb }))
+    }
+}
+
+impl<T: SimpleStaticType> SimpleStaticType for Option<T> {
+    fn get_simple_static_type() -> SimpleType {
+        let t: SubExpr<_, _> = T::get_simple_static_type().into();
+        mktype(dhall_expr!(Optional t))
+    }
+}
+
+impl<T: SimpleStaticType> SimpleStaticType for Vec<T> {
+    fn get_simple_static_type() -> SimpleType {
+        let t: SubExpr<_, _> = T::get_simple_static_type().into();
+        mktype(dhall_expr!(List t))
+    }
+}
+
+impl<'a, T: SimpleStaticType> SimpleStaticType for &'a T {
+    fn get_simple_static_type() -> SimpleType {
+        T::get_simple_static_type()
+    }
+}
+
+impl<T> SimpleStaticType for std::marker::PhantomData<T> {
+    fn get_simple_static_type() -> SimpleType {
+        mktype(dhall_expr!({}))
+    }
+}
+
+impl<T: SimpleStaticType, E: SimpleStaticType> SimpleStaticType
+    for std::result::Result<T, E>
+{
+    fn get_simple_static_type() -> SimpleType {
+        let tt: SubExpr<_, _> = T::get_simple_static_type().into();
+        let te: SubExpr<_, _> = E::get_simple_static_type().into();
+        mktype(dhall_expr!(< Ok: tt | Err: te>))
+    }
+}
diff --git a/dhall/src/typecheck.rs b/dhall/src/typecheck.rs
index 998d3ca..91846bc 100644
--- a/dhall/src/typecheck.rs
+++ b/dhall/src/typecheck.rs
@@ -13,6 +13,11 @@ impl Resolved {
     pub fn typecheck(self) -> Result<Typed, TypeError<X>> {
         type_of(self.0.clone())
     }
+    pub fn typecheck_with(self, ty: &Type) -> Result<Typed, TypeError<X>> {
+        let expr: SubExpr<_, _> = self.0.clone();
+        let ty: SubExpr<_, _> = ty.as_normalized()?.as_expr().clone();
+        type_of(dhall::subexpr!(expr: ty))
+    }
     /// Pretends this expression has been typechecked. Use with care.
     pub fn skip_typecheck(self) -> Typed {
         Typed(self.0, UNTYPE)
@@ -42,7 +47,7 @@ impl Normalized {
         &self.0
     }
     #[inline(always)]
-    fn into_expr(self) -> SubExpr<X, X> {
+    pub(crate) fn into_expr(self) -> SubExpr<X, X> {
         self.0
     }
     #[inline(always)]
@@ -50,7 +55,7 @@ impl Normalized {
         &self.1
     }
     #[inline(always)]
-    fn into_type(self) -> Type {
+    pub(crate) fn into_type(self) -> Type {
         crate::expr::Type(TypeInternal::Expr(Box::new(self)))
     }
     // Expose the outermost constructor
@@ -78,7 +83,7 @@ impl Type {
         }
     }
     #[inline(always)]
-    fn into_normalized(self) -> Result<Normalized, TypeError<X>> {
+    pub(crate) fn into_normalized(self) -> Result<Normalized, TypeError<X>> {
         use TypeInternal::*;
         match self.0 {
             Expr(e) => Ok(*e),
@@ -110,6 +115,21 @@ impl Type {
             Untyped => Untyped,
         })
     }
+
+    #[inline(always)]
+    pub fn const_sort() -> Self {
+        Normalized(rc(ExprF::Const(Const::Sort)), UNTYPE).into_type()
+    }
+    #[inline(always)]
+    pub fn const_kind() -> Self {
+        Normalized(rc(ExprF::Const(Const::Kind)), Type::const_sort())
+            .into_type()
+    }
+    #[inline(always)]
+    pub fn const_type() -> Self {
+        Normalized(rc(ExprF::Const(Const::Type)), Type::const_kind())
+            .into_type()
+    }
 }
 
 const UNTYPE: Type = Type(TypeInternal::Untyped);
@@ -706,23 +726,23 @@ mod spec_tests {
 
     macro_rules! tc_success {
         ($name:ident, $path:expr) => {
-            make_spec_test!(TypecheckSuccess, $name, $path);
+            make_spec_test!(Typecheck, Success, $name, $path);
         };
     }
     // macro_rules! tc_failure {
     //     ($name:ident, $path:expr) => {
-    //         make_spec_test!(TypecheckFailure, $name, $path);
+    //         make_spec_test!(Typecheck, Failure, $name, $path);
     //     };
     // }
 
     macro_rules! ti_success {
         ($name:ident, $path:expr) => {
-            make_spec_test!(TypeInferenceSuccess, $name, $path);
+            make_spec_test!(TypeInference, Success, $name, $path);
         };
     }
     // macro_rules! ti_failure {
     //     ($name:ident, $path:expr) => {
-    //         make_spec_test!(TypeInferenceFailure, $name, $path);
+    //         make_spec_test!(TypeInference, Failure, $name, $path);
     //     };
     // }