Reorganize dhall into a phase structure

15 files changed, 499 insertions, 477 deletions

diff --git a/dhall/src/error.rs b/dhall/src/error.rs
index 6ed0bfb..8497a91 100644
--- a/dhall/src/error.rs
+++ b/dhall/src/error.rs
@@ -1,13 +1,21 @@
+use std::io::Error as IOError;
+
+use dhall_syntax::ParseError;
+
+use crate::phase::binary::DecodeError;
+use crate::phase::resolve::ImportError;
+use crate::phase::typecheck::TypeError;
+
 pub type Result<T> = std::result::Result<T, Error>;
 
 #[derive(Debug)]
 #[non_exhaustive]
 pub enum Error {
-    IO(std::io::Error),
-    Parse(dhall_syntax::ParseError),
-    Decode(crate::binary::DecodeError),
-    Resolve(crate::imports::ImportError),
-    Typecheck(crate::typecheck::TypeError),
+    IO(IOError),
+    Parse(ParseError),
+    Decode(DecodeError),
+    Resolve(ImportError),
+    Typecheck(TypeError),
     Deserialize(String),
 }
 
@@ -25,28 +33,28 @@ impl std::fmt::Display for Error {
 }
 
 impl std::error::Error for Error {}
-impl From<std::io::Error> for Error {
-    fn from(err: std::io::Error) -> Error {
+impl From<IOError> for Error {
+    fn from(err: IOError) -> Error {
         Error::IO(err)
     }
 }
-impl From<dhall_syntax::ParseError> for Error {
-    fn from(err: dhall_syntax::ParseError) -> Error {
+impl From<ParseError> for Error {
+    fn from(err: ParseError) -> Error {
         Error::Parse(err)
     }
 }
-impl From<crate::binary::DecodeError> for Error {
-    fn from(err: crate::binary::DecodeError) -> Error {
+impl From<DecodeError> for Error {
+    fn from(err: DecodeError) -> Error {
         Error::Decode(err)
     }
 }
-impl From<crate::imports::ImportError> for Error {
-    fn from(err: crate::imports::ImportError) -> Error {
+impl From<ImportError> for Error {
+    fn from(err: ImportError) -> Error {
         Error::Resolve(err)
     }
 }
-impl From<crate::typecheck::TypeError> for Error {
-    fn from(err: crate::typecheck::TypeError) -> Error {
+impl From<TypeError> for Error {
+    fn from(err: TypeError) -> Error {
         Error::Typecheck(err)
     }
 }
diff --git a/dhall/src/expr.rs b/dhall/src/expr.rs
deleted file mode 100644
index 896753c..0000000
--- a/dhall/src/expr.rs
+++ /dev/null
@@ -1,228 +0,0 @@
-use crate::imports::ImportRoot;
-use crate::normalize::{Thunk, Value};
-use dhall_syntax::*;
-
-macro_rules! derive_other_traits {
-    ($ty:ident) => {
-        impl std::cmp::PartialEq for $ty {
-            fn eq(&self, other: &Self) -> bool {
-                self.0 == other.0
-            }
-        }
-
-        impl std::cmp::Eq for $ty {}
-
-        impl std::fmt::Display for $ty {
-            fn fmt(
-                &self,
-                f: &mut std::fmt::Formatter,
-            ) -> Result<(), std::fmt::Error> {
-                self.0.fmt(f)
-            }
-        }
-    };
-}
-
-#[derive(Debug, Clone)]
-pub(crate) struct Parsed(
-    pub(crate) SubExpr<Span, Import>,
-    pub(crate) ImportRoot,
-);
-derive_other_traits!(Parsed);
-
-#[derive(Debug, Clone)]
-pub(crate) struct Resolved(pub(crate) SubExpr<Span, Normalized>);
-derive_other_traits!(Resolved);
-
-pub(crate) use self::typed::Typed;
-
-#[derive(Debug, Clone)]
-pub(crate) struct Normalized(pub(crate) Typed);
-
-impl std::cmp::PartialEq for Normalized {
-    fn eq(&self, other: &Self) -> bool {
-        self.0 == other.0
-    }
-}
-
-impl std::cmp::Eq for Normalized {}
-
-impl std::fmt::Display for Normalized {
-    fn fmt(&self, f: &mut std::fmt::Formatter) -> Result<(), std::fmt::Error> {
-        self.to_expr().fmt(f)
-    }
-}
-
-mod typed {
-    use super::Type;
-    use crate::normalize::{AlphaVar, Thunk, Value};
-    use crate::typecheck::{
-        TypeError, TypeInternal, TypeMessage, TypecheckContext,
-    };
-    use dhall_syntax::{Const, SubExpr, X};
-    use std::borrow::Cow;
-
-    #[derive(Debug, Clone)]
-    pub(crate) enum Typed {
-        // The `Sort` higher-kinded type doesn't have a type
-        Sort,
-        // Any other value, along with its type
-        Value(Thunk, Option<Type>),
-    }
-
-    impl Typed {
-        pub(crate) fn from_thunk_and_type(th: Thunk, t: Type) -> Self {
-            Typed::Value(th, Some(t))
-        }
-
-        pub(crate) fn from_thunk_untyped(th: Thunk) -> Self {
-            Typed::Value(th, None)
-        }
-
-        // TODO: Avoid cloning if possible
-        pub(crate) fn to_value(&self) -> Value {
-            match self {
-                Typed::Value(th, _) => th.to_value(),
-                Typed::Sort => Value::Const(Const::Sort),
-            }
-        }
-
-        pub(crate) fn to_expr(&self) -> SubExpr<X, X> {
-            self.to_value().normalize_to_expr()
-        }
-
-        pub(crate) fn to_expr_alpha(&self) -> SubExpr<X, X> {
-            self.to_value().normalize_to_expr_maybe_alpha(true)
-        }
-
-        pub(crate) fn to_thunk(&self) -> Thunk {
-            match self {
-                Typed::Value(th, _) => th.clone(),
-                Typed::Sort => Thunk::from_value(Value::Const(Const::Sort)),
-            }
-        }
-
-        pub(crate) fn to_type(&self) -> Type {
-            match self {
-                Typed::Sort => Type(TypeInternal::Const(Const::Sort)),
-                Typed::Value(th, _) => match &*th.as_value() {
-                    Value::Const(c) => Type(TypeInternal::Const(*c)),
-                    _ => Type(TypeInternal::Typed(Box::new(self.clone()))),
-                },
-            }
-        }
-
-        pub(crate) fn get_type(&self) -> Result<Cow<'_, Type>, TypeError> {
-            match self {
-                Typed::Value(_, Some(t)) => Ok(Cow::Borrowed(t)),
-                Typed::Value(_, None) => Err(TypeError::new(
-                    &TypecheckContext::new(),
-                    TypeMessage::Untyped,
-                )),
-                Typed::Sort => Err(TypeError::new(
-                    &TypecheckContext::new(),
-                    TypeMessage::Sort,
-                )),
-            }
-        }
-
-        pub(crate) fn shift(&self, delta: isize, var: &AlphaVar) -> Self {
-            match self {
-                Typed::Value(th, t) => Typed::Value(
-                    th.shift(delta, var),
-                    t.as_ref().map(|x| x.shift(delta, var)),
-                ),
-                Typed::Sort => Typed::Sort,
-            }
-        }
-
-        pub(crate) fn subst_shift(&self, var: &AlphaVar, val: &Typed) -> Self {
-            match self {
-                Typed::Value(th, t) => Typed::Value(
-                    th.subst_shift(var, val),
-                    t.as_ref().map(|x| x.subst_shift(var, val)),
-                ),
-                Typed::Sort => Typed::Sort,
-            }
-        }
-        pub(crate) fn const_sort() -> Self {
-            Typed::Sort
-        }
-    }
-
-    impl std::cmp::PartialEq for Typed {
-        fn eq(&self, other: &Self) -> bool {
-            self.to_value() == other.to_value()
-        }
-    }
-
-    impl std::cmp::Eq for Typed {}
-}
-
-/// A Dhall expression representing a simple type.
-///
-/// This captures what is usually simply called a "type", like
-/// `Bool`, `{ x: Integer }` or `Natural -> Text`.
-///
-/// For a more general notion of "type", see [Type].
-#[derive(Debug, Clone)]
-pub struct SimpleType(pub(crate) SubExpr<X, X>);
-derive_other_traits!(SimpleType);
-
-pub(crate) use crate::typecheck::TypeInternal;
-
-/// A Dhall expression representing a (possibly higher-kinded) type.
-///
-/// This includes [SimpleType]s but also higher-kinded expressions like
-/// `Type`, `Kind` and `{ x: Type }`.
-#[derive(Debug, Clone, PartialEq, Eq)]
-pub struct Type(pub(crate) TypeInternal);
-
-impl std::fmt::Display for Type {
-    fn fmt(&self, f: &mut std::fmt::Formatter) -> Result<(), std::fmt::Error> {
-        self.to_normalized().fmt(f)
-    }
-}
-
-// 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)
-    }
-}
-
-// Exposed for the macros
-#[doc(hidden)]
-impl From<Normalized> for Typed {
-    fn from(x: Normalized) -> Typed {
-        x.0
-    }
-}
-
-impl Normalized {
-    pub(crate) fn from_thunk_and_type(th: Thunk, t: Type) -> Self {
-        Normalized(Typed::from_thunk_and_type(th, t))
-    }
-    pub(crate) fn to_expr(&self) -> SubExpr<X, X> {
-        self.0.to_expr()
-    }
-    #[allow(dead_code)]
-    pub(crate) fn to_expr_alpha(&self) -> SubExpr<X, X> {
-        self.0.to_expr_alpha()
-    }
-    pub(crate) fn to_value(&self) -> Value {
-        self.0.to_value()
-    }
-    pub(crate) fn to_thunk(&self) -> Thunk {
-        self.0.to_thunk()
-    }
-}
diff --git a/dhall/src/lib.rs b/dhall/src/lib.rs
index a531f64..ec110f7 100644
--- a/dhall/src/lib.rs
+++ b/dhall/src/lib.rs
@@ -123,18 +123,11 @@
 #[macro_use]
 mod tests;
 
-#[cfg(test)]
-mod parser;
-
-mod binary;
 /// When manipulating Dhall expressions goes wrong.
 pub mod error;
-pub mod expr;
-mod imports;
-mod normalize;
+mod phase;
 mod serde;
 mod traits;
-mod typecheck;
 
 /// Deserialization of Dhall expressions into Rust
 pub mod de {
@@ -153,7 +146,7 @@ pub mod de {
     /// expression has that type.
     pub fn from_str<'a, T: Deserialize<'a>>(
         s: &'a str,
-        ty: Option<&crate::expr::Type>,
+        ty: Option<&crate::phase::Type>,
     ) -> crate::error::Result<T> {
         T::from_str(s, ty)
     }
diff --git a/dhall/src/parser.rs b/dhall/src/parser.rs
deleted file mode 100644
index 3648c4f..0000000
--- a/dhall/src/parser.rs
+++ /dev/null
@@ -1,6 +0,0 @@
-#[cfg(test)]
-mod spec_tests {
-    #![rustfmt::skip]
-    // See ../build.rs
-    include!(concat!(env!("OUT_DIR"), "/parser_tests.rs"));
-}
diff --git a/dhall/src/binary.rs b/dhall/src/phase/binary.rs
index 9c31d4c..9c31d4c 100644
--- a/dhall/src/binary.rs
+++ b/dhall/src/phase/binary.rs
diff --git a/dhall/src/phase/mod.rs b/dhall/src/phase/mod.rs
new file mode 100644
index 0000000..0b6eca6
--- /dev/null
+++ b/dhall/src/phase/mod.rs
@@ -0,0 +1,389 @@
+use std::borrow::Cow;
+use std::fmt::Display;
+use std::path::Path;
+
+use dhall_syntax::{Const, Import, Span, SubExpr, X};
+
+use crate::error::Error;
+
+use normalize::{AlphaVar, Thunk, Value};
+use resolve::{ImportError, ImportRoot};
+use typecheck::{
+    const_to_typed, type_of_const, TypeError, TypeMessage, TypecheckContext,
+};
+
+pub(crate) mod binary;
+pub(crate) mod normalize;
+pub(crate) mod parse;
+pub(crate) mod resolve;
+pub(crate) mod typecheck;
+
+pub(crate) type ParsedSubExpr = SubExpr<Span, Import>;
+pub(crate) type ResolvedSubExpr = SubExpr<Span, Normalized>;
+pub(crate) type NormalizedSubExpr = SubExpr<X, X>;
+
+#[derive(Debug, Clone)]
+pub(crate) struct Parsed(pub(crate) ParsedSubExpr, pub(crate) ImportRoot);
+
+/// An expression where all imports have been resolved
+#[derive(Debug, Clone)]
+pub(crate) struct Resolved(pub(crate) ResolvedSubExpr);
+
+/// A typed expression
+#[derive(Debug, Clone)]
+pub(crate) enum Typed {
+    // The `Sort` higher-kinded type; it doesn't have a type
+    Sort,
+    // Any other value, along with (optionally) its type
+    Value(Thunk, Option<Type>),
+}
+
+/// A normalized expression.
+///
+/// Invariant: the contained Typed expression must be in normal form,
+#[derive(Debug, Clone)]
+pub(crate) struct Normalized(pub(crate) Typed);
+
+/// A Dhall expression representing a simple type.
+///
+/// This captures what is usually simply called a "type", like
+/// `Bool`, `{ x: Integer }` or `Natural -> Text`.
+///
+/// For a more general notion of "type", see [Type].
+#[derive(Debug, Clone)]
+pub struct SimpleType(pub(crate) NormalizedSubExpr);
+
+/// A Dhall expression representing a (possibly higher-kinded) type.
+///
+/// This includes [SimpleType]s but also higher-kinded expressions like
+/// `Type`, `Kind` and `{ x: Type }`.
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct Type(pub(crate) TypeInternal);
+
+#[derive(Debug, Clone)]
+pub(crate) enum TypeInternal {
+    Const(Const),
+    /// This must not contain a Const value.
+    Typed(Box<Typed>),
+}
+
+impl Parsed {
+    pub fn parse_file(f: &Path) -> Result<Parsed, Error> {
+        parse::parse_file(f)
+    }
+
+    pub fn parse_str(s: &str) -> Result<Parsed, Error> {
+        parse::parse_str(s)
+    }
+
+    #[allow(dead_code)]
+    pub fn parse_binary_file(f: &Path) -> Result<Parsed, Error> {
+        parse::parse_binary_file(f)
+    }
+
+    pub fn resolve(self) -> Result<Resolved, ImportError> {
+        resolve::resolve(self)
+    }
+
+    #[allow(dead_code)]
+    pub fn skip_resolve(self) -> Result<Resolved, ImportError> {
+        resolve::skip_resolve_expr(self)
+    }
+}
+
+impl Resolved {
+    pub fn typecheck(self) -> Result<Typed, TypeError> {
+        typecheck::typecheck(self)
+    }
+    pub fn typecheck_with(self, ty: &Type) -> Result<Typed, TypeError> {
+        typecheck::typecheck_with(self, ty)
+    }
+    /// Pretends this expression has been typechecked. Use with care.
+    #[allow(dead_code)]
+    pub fn skip_typecheck(self) -> Typed {
+        typecheck::skip_typecheck(self)
+    }
+}
+
+impl Typed {
+    /// Reduce an expression to its normal form, performing beta reduction
+    ///
+    /// `normalize` does not type-check the expression.  You may want to type-check
+    /// expressions before normalizing them since normalization can convert an
+    /// ill-typed expression into a well-typed expression.
+    ///
+    /// However, `normalize` will not fail if the expression is ill-typed and will
+    /// leave ill-typed sub-expressions unevaluated.
+    pub fn normalize(self) -> Normalized {
+        match &self {
+            Typed::Sort => {}
+            Typed::Value(thunk, _) => {
+                thunk.normalize_nf();
+            }
+        }
+        Normalized(self)
+    }
+
+    pub(crate) fn from_thunk_and_type(th: Thunk, t: Type) -> Self {
+        Typed::Value(th, Some(t))
+    }
+    pub(crate) fn from_thunk_untyped(th: Thunk) -> Self {
+        Typed::Value(th, None)
+    }
+
+    // TODO: Avoid cloning if possible
+    pub(crate) fn to_value(&self) -> Value {
+        match self {
+            Typed::Value(th, _) => th.to_value(),
+            Typed::Sort => Value::Const(Const::Sort),
+        }
+    }
+    pub(crate) fn to_expr(&self) -> NormalizedSubExpr {
+        self.to_value().normalize_to_expr()
+    }
+    pub(crate) fn to_expr_alpha(&self) -> NormalizedSubExpr {
+        self.to_value().normalize_to_expr_maybe_alpha(true)
+    }
+    pub(crate) fn to_thunk(&self) -> Thunk {
+        match self {
+            Typed::Value(th, _) => th.clone(),
+            Typed::Sort => Thunk::from_value(Value::Const(Const::Sort)),
+        }
+    }
+    pub(crate) fn to_type(&self) -> Type {
+        match self {
+            Typed::Sort => Type(TypeInternal::Const(Const::Sort)),
+            Typed::Value(th, _) => match &*th.as_value() {
+                Value::Const(c) => Type(TypeInternal::Const(*c)),
+                _ => Type(TypeInternal::Typed(Box::new(self.clone()))),
+            },
+        }
+    }
+
+    pub(crate) fn get_type(&self) -> Result<Cow<'_, Type>, TypeError> {
+        match self {
+            Typed::Value(_, Some(t)) => Ok(Cow::Borrowed(t)),
+            Typed::Value(_, None) => Err(TypeError::new(
+                &TypecheckContext::new(),
+                TypeMessage::Untyped,
+            )),
+            Typed::Sort => {
+                Err(TypeError::new(&TypecheckContext::new(), TypeMessage::Sort))
+            }
+        }
+    }
+
+    pub(crate) fn const_sort() -> Self {
+        Typed::Sort
+    }
+
+    pub(crate) fn shift(&self, delta: isize, var: &AlphaVar) -> Self {
+        match self {
+            Typed::Value(th, t) => Typed::Value(
+                th.shift(delta, var),
+                t.as_ref().map(|x| x.shift(delta, var)),
+            ),
+            Typed::Sort => Typed::Sort,
+        }
+    }
+
+    pub(crate) fn subst_shift(&self, var: &AlphaVar, val: &Typed) -> Self {
+        match self {
+            Typed::Value(th, t) => Typed::Value(
+                th.subst_shift(var, val),
+                t.as_ref().map(|x| x.subst_shift(var, val)),
+            ),
+            Typed::Sort => Typed::Sort,
+        }
+    }
+}
+
+impl Type {
+    pub(crate) fn to_normalized(&self) -> Normalized {
+        self.0.to_normalized()
+    }
+    pub(crate) fn to_expr(&self) -> NormalizedSubExpr {
+        self.0.to_expr()
+    }
+    pub(crate) fn to_value(&self) -> Value {
+        self.0.to_value()
+    }
+    pub(crate) fn as_const(&self) -> Option<Const> {
+        self.0.as_const()
+    }
+    pub(crate) fn internal_whnf(&self) -> Option<Value> {
+        self.0.whnf()
+    }
+    pub(crate) fn get_type(&self) -> Result<Cow<'_, Type>, TypeError> {
+        self.0.get_type()
+    }
+
+    pub(crate) fn const_sort() -> Self {
+        Type(TypeInternal::Const(Const::Sort))
+    }
+    pub(crate) fn const_kind() -> Self {
+        Type(TypeInternal::Const(Const::Kind))
+    }
+    pub(crate) fn const_type() -> Self {
+        Type(TypeInternal::Const(Const::Type))
+    }
+
+    pub(crate) fn shift(&self, delta: isize, var: &AlphaVar) -> Self {
+        Type(self.0.shift(delta, var))
+    }
+    pub(crate) fn subst_shift(&self, var: &AlphaVar, val: &Typed) -> Self {
+        Type(self.0.subst_shift(var, val))
+    }
+}
+
+impl TypeInternal {
+    pub(crate) fn to_typed(&self) -> Typed {
+        match self {
+            TypeInternal::Typed(e) => e.as_ref().clone(),
+            TypeInternal::Const(c) => const_to_typed(*c),
+        }
+    }
+    pub(crate) fn to_normalized(&self) -> Normalized {
+        self.to_typed().normalize()
+    }
+    pub(crate) fn to_expr(&self) -> NormalizedSubExpr {
+        self.to_normalized().to_expr()
+    }
+    pub(crate) fn to_value(&self) -> Value {
+        self.to_typed().to_value()
+    }
+    pub(crate) fn get_type(&self) -> Result<Cow<'_, Type>, TypeError> {
+        Ok(match self {
+            TypeInternal::Typed(e) => e.get_type()?,
+            TypeInternal::Const(c) => Cow::Owned(type_of_const(*c)?),
+        })
+    }
+    pub(crate) fn as_const(&self) -> Option<Const> {
+        match self {
+            TypeInternal::Const(c) => Some(*c),
+            _ => None,
+        }
+    }
+    pub(crate) fn whnf(&self) -> Option<Value> {
+        match self {
+            TypeInternal::Typed(e) => Some(e.to_value()),
+            _ => None,
+        }
+    }
+    pub(crate) fn shift(&self, delta: isize, var: &AlphaVar) -> Self {
+        use TypeInternal::*;
+        match self {
+            Typed(e) => Typed(Box::new(e.shift(delta, var))),
+            Const(c) => Const(*c),
+        }
+    }
+    pub(crate) fn subst_shift(&self, var: &AlphaVar, val: &Typed) -> Self {
+        use TypeInternal::*;
+        match self {
+            Typed(e) => Typed(Box::new(e.subst_shift(var, val))),
+            Const(c) => Const(*c),
+        }
+    }
+}
+
+impl Normalized {
+    pub(crate) fn from_thunk_and_type(th: Thunk, t: Type) -> Self {
+        Normalized(Typed::from_thunk_and_type(th, t))
+    }
+
+    pub(crate) fn to_expr(&self) -> NormalizedSubExpr {
+        self.0.to_expr()
+    }
+    #[allow(dead_code)]
+    pub(crate) fn to_expr_alpha(&self) -> NormalizedSubExpr {
+        self.0.to_expr_alpha()
+    }
+    pub(crate) fn to_value(&self) -> Value {
+        self.0.to_value()
+    }
+    pub(crate) fn to_thunk(&self) -> Thunk {
+        self.0.to_thunk()
+    }
+    pub(crate) fn to_type(self) -> Type {
+        self.0.to_type()
+    }
+    pub(crate) fn shift(&self, delta: isize, var: &AlphaVar) -> Self {
+        Normalized(self.0.shift(delta, var))
+    }
+}
+
+macro_rules! derive_traits_for_wrapper_struct {
+    ($ty:ident) => {
+        impl std::cmp::PartialEq for $ty {
+            fn eq(&self, other: &Self) -> bool {
+                self.0 == other.0
+            }
+        }
+
+        impl std::cmp::Eq for $ty {}
+
+        impl std::fmt::Display for $ty {
+            fn fmt(
+                &self,
+                f: &mut std::fmt::Formatter,
+            ) -> Result<(), std::fmt::Error> {
+                self.0.fmt(f)
+            }
+        }
+    };
+}
+
+derive_traits_for_wrapper_struct!(Parsed);
+derive_traits_for_wrapper_struct!(Resolved);
+derive_traits_for_wrapper_struct!(Normalized);
+derive_traits_for_wrapper_struct!(SimpleType);
+
+impl Eq for Typed {}
+impl PartialEq for Typed {
+    fn eq(&self, other: &Self) -> bool {
+        self.to_value() == other.to_value()
+    }
+}
+
+impl Eq for TypeInternal {}
+impl PartialEq for TypeInternal {
+    fn eq(&self, other: &Self) -> bool {
+        self.to_normalized() == other.to_normalized()
+    }
+}
+
+impl Display for Typed {
+    fn fmt(&self, f: &mut std::fmt::Formatter) -> Result<(), std::fmt::Error> {
+        self.to_expr().fmt(f)
+    }
+}
+
+impl Display for Type {
+    fn fmt(&self, f: &mut std::fmt::Formatter) -> Result<(), std::fmt::Error> {
+        self.to_normalized().fmt(f)
+    }
+}
+
+// Exposed for the macros
+#[doc(hidden)]
+impl From<SimpleType> for NormalizedSubExpr {
+    fn from(x: SimpleType) -> NormalizedSubExpr {
+        x.0
+    }
+}
+
+// Exposed for the macros
+#[doc(hidden)]
+impl From<NormalizedSubExpr> for SimpleType {
+    fn from(x: NormalizedSubExpr) -> SimpleType {
+        SimpleType(x)
+    }
+}
+
+// Exposed for the macros
+#[doc(hidden)]
+impl From<Normalized> for Typed {
+    fn from(x: Normalized) -> Typed {
+        x.0
+    }
+}
diff --git a/dhall/src/normalize.rs b/dhall/src/phase/normalize.rs
index 1d306bc..2340bbd 100644
--- a/dhall/src/normalize.rs
+++ b/dhall/src/phase/normalize.rs
@@ -6,34 +6,13 @@ use dhall_proc_macros as dhall;
 use dhall_syntax::context::Context;
 use dhall_syntax::{
     rc, BinOp, Builtin, Const, ExprF, Integer, InterpolatedTextContents, Label,
-    Natural, Span, SubExpr, V, X,
+    Natural, V, X,
 };
 
-use crate::expr::{Normalized, Type, Typed};
-
-type InputSubExpr = SubExpr<Span, Normalized>;
-type OutputSubExpr = SubExpr<X, X>;
-
-impl Typed {
-    /// Reduce an expression to its normal form, performing beta reduction
-    ///
-    /// `normalize` does not type-check the expression.  You may want to type-check
-    /// expressions before normalizing them since normalization can convert an
-    /// ill-typed expression into a well-typed expression.
-    ///
-    /// However, `normalize` will not fail if the expression is ill-typed and will
-    /// leave ill-typed sub-expressions unevaluated.
-    ///
-    pub fn normalize(self) -> Normalized {
-        match &self {
-            Typed::Sort => {}
-            Typed::Value(thunk, _) => {
-                thunk.normalize_nf();
-            }
-        }
-        Normalized(self)
-    }
-}
+use crate::phase::{NormalizedSubExpr, ResolvedSubExpr, Type, Typed};
+
+type InputSubExpr = ResolvedSubExpr;
+type OutputSubExpr = NormalizedSubExpr;
 
 /// Stores a pair of variables: a normal one and if relevant one
 /// that corresponds to the alpha-normalized version of the first one.
@@ -186,9 +165,9 @@ impl NormalizationContext {
         }
     }
     pub(crate) fn from_typecheck_ctx(
-        tc_ctx: &crate::typecheck::TypecheckContext,
+        tc_ctx: &crate::phase::typecheck::TypecheckContext,
     ) -> Self {
-        use crate::typecheck::EnvItem::*;
+        use crate::phase::typecheck::EnvItem::*;
         let mut ctx = Context::new();
         for (k, vs) in tc_ctx.0.iter_keys() {
             for v in vs.iter() {
@@ -718,7 +697,7 @@ mod thunk {
         apply_any, normalize_whnf, AlphaVar, InputSubExpr,
         NormalizationContext, OutputSubExpr, Value,
     };
-    use crate::expr::Typed;
+    use crate::phase::Typed;
     use std::cell::{Ref, RefCell};
     use std::rc::Rc;
 
diff --git a/dhall/src/phase/parse.rs b/dhall/src/phase/parse.rs
new file mode 100644
index 0000000..809faf4
--- /dev/null
+++ b/dhall/src/phase/parse.rs
@@ -0,0 +1,38 @@
+use std::fs::File;
+use std::io::Read;
+use std::path::Path;
+
+use dhall_syntax::parse_expr;
+
+use crate::error::Error;
+use crate::phase::resolve::ImportRoot;
+use crate::phase::Parsed;
+
+pub(crate) 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)?;
+    let root = ImportRoot::LocalDir(f.parent().unwrap().to_owned());
+    Ok(Parsed(expr.unnote().note_absurd(), root))
+}
+
+pub(crate) 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(crate) 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::phase::binary::decode(&buffer)?;
+    let root = ImportRoot::LocalDir(f.parent().unwrap().to_owned());
+    Ok(Parsed(expr.note_absurd(), root))
+}
+
+#[cfg(test)]
+mod spec_tests {
+    #![rustfmt::skip]
+    // See build.rs
+    include!(concat!(env!("OUT_DIR"), "/parser_tests.rs"));
+}
diff --git a/dhall/src/imports.rs b/dhall/src/phase/resolve.rs
index 87642a2..afb49cb 100644
--- a/dhall/src/imports.rs
+++ b/dhall/src/phase/resolve.rs
@@ -1,11 +1,10 @@
-use crate::error::Error;
-use crate::expr::*;
-use dhall_syntax::*;
 use std::collections::HashMap;
-use std::fs::File;
-use std::io::Read;
-use std::path::Path;
-use std::path::PathBuf;
+use std::path::{Path, PathBuf};
+
+use dhall_syntax::Import;
+
+use crate::error::Error;
+use crate::phase::{Normalized, Parsed, Resolved};
 
 #[derive(Debug)]
 pub enum ImportError {
@@ -97,7 +96,11 @@ fn do_resolve_expr(
     Ok(Resolved(expr))
 }
 
-fn skip_resolve_expr(
+pub(crate) fn resolve(e: Parsed) -> Result<Resolved, ImportError> {
+    do_resolve_expr(e, &mut HashMap::new(), &Vec::new())
+}
+
+pub(crate) fn skip_resolve_expr(
     Parsed(expr, _root): Parsed,
 ) -> Result<Resolved, ImportError> {
     let resolve = |import: &Import| -> Result<Normalized, ImportError> {
@@ -107,40 +110,6 @@ fn skip_resolve_expr(
     Ok(Resolved(expr))
 }
 
-impl Parsed {
-    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)?;
-        let root = ImportRoot::LocalDir(f.parent().unwrap().to_owned());
-        Ok(Parsed(expr.unnote().note_absurd(), root))
-    }
-
-    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))
-    }
-
-    #[allow(dead_code)]
-    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)?;
-        let root = ImportRoot::LocalDir(f.parent().unwrap().to_owned());
-        Ok(Parsed(expr.note_absurd(), root))
-    }
-
-    pub fn resolve(self) -> Result<Resolved, ImportError> {
-        crate::imports::do_resolve_expr(self, &mut HashMap::new(), &Vec::new())
-    }
-
-    #[allow(dead_code)]
-    pub fn skip_resolve(self) -> Result<Resolved, ImportError> {
-        crate::imports::skip_resolve_expr(self)
-    }
-}
-
 #[cfg(test)]
 mod spec_tests {
     #![rustfmt::skip]
diff --git a/dhall/src/typecheck.rs b/dhall/src/phase/typecheck.rs
index 4dde883..6b12077 100644
--- a/dhall/src/typecheck.rs
+++ b/dhall/src/phase/typecheck.rs
@@ -4,10 +4,10 @@ use std::borrow::Cow;
 use std::collections::BTreeMap;
 use std::fmt;
 
-use crate::expr::*;
-use crate::normalize::{
+use crate::phase::normalize::{
     AlphaVar, NormalizationContext, Thunk, TypeThunk, Value,
 };
+use crate::phase::*;
 use crate::traits::DynamicType;
 use dhall_proc_macros as dhall;
 use dhall_syntax;
@@ -16,71 +16,6 @@ use dhall_syntax::*;
 
 use self::TypeMessage::*;
 
-impl Resolved {
-    pub fn typecheck(self) -> Result<Typed, TypeError> {
-        type_of(self.0)
-    }
-    pub fn typecheck_with(self, ty: &Type) -> Result<Typed, TypeError> {
-        let expr: SubExpr<_, _> = self.0;
-        let ty: SubExpr<_, _> = ty.to_expr().embed_absurd().note_absurd();
-        type_of(expr.rewrap(ExprF::Annot(expr.clone(), ty)))
-    }
-    /// Pretends this expression has been typechecked. Use with care.
-    #[allow(dead_code)]
-    pub fn skip_typecheck(self) -> Typed {
-        Typed::from_thunk_untyped(Thunk::new(
-            NormalizationContext::new(),
-            self.0,
-        ))
-    }
-}
-
-impl Normalized {
-    fn shift(&self, delta: isize, var: &AlphaVar) -> Self {
-        Normalized(self.0.shift(delta, var))
-    }
-    pub(crate) fn to_type(self) -> Type {
-        self.0.to_type()
-    }
-}
-
-impl Type {
-    pub(crate) fn to_normalized(&self) -> Normalized {
-        self.0.to_normalized()
-    }
-    pub(crate) fn to_expr(&self) -> SubExpr<X, X> {
-        self.0.to_expr()
-    }
-    pub(crate) fn to_value(&self) -> Value {
-        self.0.to_value()
-    }
-    pub(crate) fn get_type(&self) -> Result<Cow<'_, Type>, TypeError> {
-        self.0.get_type()
-    }
-    fn as_const(&self) -> Option<Const> {
-        self.0.as_const()
-    }
-    fn internal_whnf(&self) -> Option<Value> {
-        self.0.whnf()
-    }
-    pub(crate) fn shift(&self, delta: isize, var: &AlphaVar) -> Self {
-        Type(self.0.shift(delta, var))
-    }
-    pub(crate) fn subst_shift(&self, var: &AlphaVar, val: &Typed) -> Self {
-        Type(self.0.subst_shift(var, val))
-    }
-
-    fn const_sort() -> Self {
-        Type(TypeInternal::Const(Const::Sort))
-    }
-    fn const_kind() -> Self {
-        Type(TypeInternal::Const(Const::Kind))
-    }
-    pub(crate) fn const_type() -> Self {
-        Type(TypeInternal::Const(Const::Type))
-    }
-}
-
 impl TypeThunk {
     fn to_type(&self, ctx: &TypecheckContext) -> Result<Type, TypeError> {
         match self {
@@ -93,74 +28,6 @@ impl TypeThunk {
     }
 }
 
-/// A semantic type. This is partially redundant with `dhall_syntax::Expr`, on purpose. `TypeInternal` should
-/// be limited to syntactic expressions: either written by the user or meant to be printed.
-/// The rule is the following: we must _not_ construct values of type `Expr` while typechecking,
-/// but only construct `TypeInternal`s.
-#[derive(Debug, Clone)]
-pub(crate) enum TypeInternal {
-    Const(Const),
-    /// This must not contain a Const value.
-    Typed(Box<Typed>),
-}
-
-impl TypeInternal {
-    fn to_typed(&self) -> Typed {
-        match self {
-            TypeInternal::Typed(e) => e.as_ref().clone(),
-            TypeInternal::Const(c) => const_to_typed(*c),
-        }
-    }
-    fn to_normalized(&self) -> Normalized {
-        self.to_typed().normalize()
-    }
-    fn to_expr(&self) -> SubExpr<X, X> {
-        self.to_normalized().to_expr()
-    }
-    fn to_value(&self) -> Value {
-        self.to_typed().to_value()
-    }
-    pub(crate) fn get_type(&self) -> Result<Cow<'_, Type>, TypeError> {
-        Ok(match self {
-            TypeInternal::Typed(e) => e.get_type()?,
-            TypeInternal::Const(c) => Cow::Owned(type_of_const(*c)?),
-        })
-    }
-    fn as_const(&self) -> Option<Const> {
-        match self {
-            TypeInternal::Const(c) => Some(*c),
-            _ => None,
-        }
-    }
-    fn whnf(&self) -> Option<Value> {
-        match self {
-            TypeInternal::Typed(e) => Some(e.to_value()),
-            _ => None,
-        }
-    }
-    fn shift(&self, delta: isize, var: &AlphaVar) -> Self {
-        use TypeInternal::*;
-        match self {
-            Typed(e) => Typed(Box::new(e.shift(delta, var))),
-            Const(c) => Const(*c),
-        }
-    }
-    fn subst_shift(&self, var: &AlphaVar, val: &Typed) -> Self {
-        use TypeInternal::*;
-        match self {
-            Typed(e) => Typed(Box::new(e.subst_shift(var, val))),
-            Const(c) => Const(*c),
-        }
-    }
-}
-
-impl Eq for TypeInternal {}
-impl PartialEq for TypeInternal {
-    fn eq(&self, other: &Self) -> bool {
-        self.to_normalized() == other.to_normalized()
-    }
-}
-
 #[derive(Debug, Clone)]
 pub(crate) enum EnvItem {
     Type(AlphaVar, Type),
@@ -237,7 +104,7 @@ where
     eL0.borrow().to_value() == eR0.borrow().to_value()
 }
 
-fn const_to_typed(c: Const) -> Typed {
+pub(crate) fn const_to_typed(c: Const) -> Typed {
     match c {
         Const::Sort => Typed::const_sort(),
         _ => Typed::from_thunk_and_type(
@@ -251,7 +118,7 @@ fn const_to_type(c: Const) -> Type {
     Type(TypeInternal::Const(c))
 }
 
-fn type_of_const(c: Const) -> Result<Type, TypeError> {
+pub(crate) fn type_of_const(c: Const) -> Result<Type, TypeError> {
     match c {
         Const::Type => Ok(Type::const_kind()),
         Const::Kind => Ok(Type::const_sort()),
@@ -918,6 +785,22 @@ fn type_of(e: SubExpr<Span, Normalized>) -> Result<Typed, TypeError> {
     Ok(e)
 }
 
+pub(crate) fn typecheck(e: Resolved) -> Result<Typed, TypeError> {
+    type_of(e.0)
+}
+
+pub(crate) fn typecheck_with(
+    e: Resolved,
+    ty: &Type,
+) -> Result<Typed, TypeError> {
+    let expr: SubExpr<_, _> = e.0;
+    let ty: SubExpr<_, _> = ty.to_expr().embed_absurd().note_absurd();
+    type_of(expr.rewrap(ExprF::Annot(expr.clone(), ty)))
+}
+pub(crate) fn skip_typecheck(e: Resolved) -> Typed {
+    Typed::from_thunk_untyped(Thunk::new(NormalizationContext::new(), e.0))
+}
+
 /// The specific type error
 #[derive(Debug)]
 pub(crate) enum TypeMessage {
diff --git a/dhall/src/serde.rs b/dhall/src/serde.rs
index 96bc765..93921ba 100644
--- a/dhall/src/serde.rs
+++ b/dhall/src/serde.rs
@@ -1,5 +1,5 @@
 use crate::error::{Error, Result};
-use crate::expr::{Normalized, Type};
+use crate::phase::{Normalized, Type};
 use crate::traits::Deserialize;
 use dhall_syntax::*;
 use std::borrow::Cow;
diff --git a/dhall/src/tests.rs b/dhall/src/tests.rs
index 6b2ab60..18f6917 100644
--- a/dhall/src/tests.rs
+++ b/dhall/src/tests.rs
@@ -34,7 +34,7 @@ macro_rules! make_spec_test {
 }
 
 use crate::error::{Error, Result};
-use crate::expr::Parsed;
+use crate::phase::Parsed;
 use crate::traits::DynamicType;
 use std::path::PathBuf;
 
diff --git a/dhall/src/traits/deserialize.rs b/dhall/src/traits/deserialize.rs
index e3ff2d5..9673cf9 100644
--- a/dhall/src/traits/deserialize.rs
+++ b/dhall/src/traits/deserialize.rs
@@ -1,5 +1,5 @@
 use crate::error::*;
-use crate::expr::*;
+use crate::phase::*;
 
 /// A data structure that can be deserialized from a Dhall expression
 ///
diff --git a/dhall/src/traits/dynamic_type.rs b/dhall/src/traits/dynamic_type.rs
index 4c8e1fd..3f8d117 100644
--- a/dhall/src/traits/dynamic_type.rs
+++ b/dhall/src/traits/dynamic_type.rs
@@ -1,9 +1,6 @@
-use crate::expr::*;
+use crate::phase::typecheck::TypeError;
+use crate::phase::*;
 use crate::traits::StaticType;
-#[allow(unused_imports)]
-use crate::typecheck::{TypeError, TypeMessage, TypecheckContext};
-#[allow(unused_imports)]
-use dhall_syntax::{Const, ExprF};
 use std::borrow::Cow;
 
 pub trait DynamicType {
diff --git a/dhall/src/traits/static_type.rs b/dhall/src/traits/static_type.rs
index f90b8df..8b141a0 100644
--- a/dhall/src/traits/static_type.rs
+++ b/dhall/src/traits/static_type.rs
@@ -1,4 +1,4 @@
-use crate::expr::*;
+use crate::phase::*;
 use dhall_proc_macros as dhall;
 use dhall_syntax::*;
 
@@ -38,8 +38,8 @@ fn mktype(x: SubExpr<X, X>) -> SimpleType {
 
 impl<T: SimpleStaticType> StaticType for T {
     fn get_static_type() -> Type {
-        crate::expr::Normalized::from_thunk_and_type(
-            crate::normalize::Thunk::from_normalized_expr(
+        crate::phase::Normalized::from_thunk_and_type(
+            crate::phase::normalize::Thunk::from_normalized_expr(
                 T::get_simple_static_type().into(),
             ),
             Type::const_type(),