Rename TyExpr to Tir

1 files changed, 193 insertions, 0 deletions

diff --git a/dhall/src/semantics/tck/tir.rs b/dhall/src/semantics/tck/tir.rs
new file mode 100644
index 0000000..800d1b7
--- /dev/null
+++ b/dhall/src/semantics/tck/tir.rs
@@ -0,0 +1,193 @@
+use crate::error::{ErrorBuilder, TypeError};
+use crate::semantics::{mkerr, Hir, NzEnv, TyEnv, Value, ValueKind, VarEnv};
+use crate::syntax::{Builtin, Const, Span};
+use crate::{NormalizedExpr, ToExprOptions};
+
+/// The type of a type. 0 is `Type`, 1 is `Kind`, etc...
+#[derive(Debug, Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Default)]
+pub(crate) struct Universe(u8);
+
+/// An expression representing a type
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub(crate) struct Type {
+    val: Value,
+    univ: Universe,
+}
+
+/// A hir expression plus its inferred type.
+/// Stands for "Typed intermediate representation"
+#[derive(Debug, Clone)]
+pub(crate) struct Tir {
+    hir: Hir,
+    ty: Type,
+}
+
+impl Universe {
+    pub fn from_const(c: Const) -> Self {
+        Universe(match c {
+            Const::Type => 0,
+            Const::Kind => 1,
+            Const::Sort => 2,
+        })
+    }
+    pub fn as_const(self) -> Option<Const> {
+        match self.0 {
+            0 => Some(Const::Type),
+            1 => Some(Const::Kind),
+            2 => Some(Const::Sort),
+            _ => None,
+        }
+    }
+    pub fn next(self) -> Self {
+        Universe(self.0 + 1)
+    }
+}
+
+impl Type {
+    pub fn new(val: Value, univ: Universe) -> Self {
+        Type { val, univ }
+    }
+    /// Creates a new Type and infers its universe by re-typechecking its value.
+    /// TODO: ideally avoid this function altogether. Would need to store types in RecordType and
+    /// PiClosure.
+    pub fn new_infer_universe(
+        env: &TyEnv,
+        val: Value,
+    ) -> Result<Self, TypeError> {
+        let c = val.to_hir(env.as_varenv()).typecheck(env)?.ty().as_const();
+        let u = match c {
+            Some(c) => c.to_universe(),
+            None => unreachable!(
+                "internal type error: this is not a type: {:?}",
+                val
+            ),
+        };
+        Ok(Type::new(val, u))
+    }
+    pub fn from_const(c: Const) -> Self {
+        Self::new(Value::from_const(c), c.to_universe().next())
+    }
+    pub fn from_builtin(b: Builtin) -> Self {
+        use Builtin::*;
+        match b {
+            Bool | Natural | Integer | Double | Text => {}
+            _ => unreachable!("this builtin is not a type: {}", b),
+        }
+
+        Self::new(Value::from_builtin(b), Universe::from_const(Const::Type))
+    }
+
+    /// Get the type of this type
+    pub fn ty(&self) -> Universe {
+        self.univ
+    }
+
+    pub fn to_value(&self) -> Value {
+        self.val.clone()
+    }
+    pub fn as_value(&self) -> &Value {
+        &self.val
+    }
+    pub fn into_value(self) -> Value {
+        self.val
+    }
+    pub fn as_const(&self) -> Option<Const> {
+        self.val.as_const()
+    }
+    pub fn kind(&self) -> &ValueKind {
+        self.val.kind()
+    }
+
+    pub fn to_hir(&self, venv: VarEnv) -> Hir {
+        self.val.to_hir(venv)
+    }
+    pub fn to_expr_tyenv(&self, tyenv: &TyEnv) -> NormalizedExpr {
+        self.val.to_hir(tyenv.as_varenv()).to_expr_tyenv(tyenv)
+    }
+}
+
+impl Tir {
+    pub fn from_hir(hir: &Hir, ty: Type) -> Self {
+        Tir {
+            hir: hir.clone(),
+            ty,
+        }
+    }
+
+    pub fn span(&self) -> Span {
+        self.as_hir().span()
+    }
+    pub fn ty(&self) -> &Type {
+        &self.ty
+    }
+
+    pub fn to_hir(&self) -> Hir {
+        self.as_hir().clone()
+    }
+    pub fn as_hir(&self) -> &Hir {
+        &self.hir
+    }
+    /// Converts a closed expression back to the corresponding AST expression.
+    pub fn to_expr(&self, opts: ToExprOptions) -> NormalizedExpr {
+        self.as_hir().to_expr(opts)
+    }
+    pub fn to_expr_tyenv(&self, env: &TyEnv) -> NormalizedExpr {
+        self.as_hir().to_expr_tyenv(env)
+    }
+
+    /// Eval the Tir. It will actually get evaluated only as needed on demand.
+    pub fn eval(&self, env: impl Into<NzEnv>) -> Value {
+        self.as_hir().eval(env.into())
+    }
+    pub fn ensure_is_type(&self, env: &TyEnv) -> Result<(), TypeError> {
+        if self.ty().as_const().is_none() {
+            return mkerr(
+                ErrorBuilder::new(format!(
+                    "Expected a type, found: `{}`",
+                    self.to_expr_tyenv(env),
+                ))
+                .span_err(
+                    self.span(),
+                    format!(
+                        "this has type: `{}`",
+                        self.ty().to_expr_tyenv(env)
+                    ),
+                )
+                .help(format!(
+                    "An expression in type position must have type `Type`, \
+                     `Kind` or `Sort`",
+                ))
+                .format(),
+            );
+        }
+        Ok(())
+    }
+    /// Evaluate to a Type.
+    pub fn eval_to_type(&self, env: &TyEnv) -> Result<Type, TypeError> {
+        self.ensure_is_type(env)?;
+        Ok(Type::new(
+            self.eval(env),
+            self.ty()
+                .as_const()
+                .expect("case handled in ensure_is_type")
+                .to_universe(),
+        ))
+    }
+    /// Eval a closed Tir (i.e. without free variables). It will actually get evaluated only as
+    /// needed on demand.
+    pub fn eval_closed_expr(&self) -> Value {
+        self.eval(NzEnv::new())
+    }
+    /// Eval a closed Tir fully and recursively;
+    pub fn rec_eval_closed_expr(&self) -> Value {
+        let val = self.eval_closed_expr();
+        val.normalize();
+        val
+    }
+}
+
+impl From<Const> for Universe {
+    fn from(x: Const) -> Universe {
+        Universe::from_const(x)
+    }
+}