1 files changed, 389 insertions, 0 deletions
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
+    }
+}