Generalise Context on its type of keys

3 files changed, 28 insertions, 22 deletions

diff --git a/dhall/src/typecheck.rs b/dhall/src/typecheck.rs
index e36a6fa..23ab7a6 100644
--- a/dhall/src/typecheck.rs
+++ b/dhall/src/typecheck.rs
@@ -146,7 +146,7 @@ where
 }
 
 fn op2_type<'i, S, EF>(
-    ctx: &Context<'i, Expr<'i, S, X>>,
+    ctx: &Context<&'i str, Expr<'i, S, X>>,
     e: &Expr<'i, S, X>,
     t: core::Builtin,
     ef: EF,
@@ -179,7 +179,7 @@ where
 /// is not necessary for just type-checking.  If you actually care about the
 /// returned type then you may want to `normalize` it afterwards.
 pub fn type_with<'i, S>(
-    ctx: &Context<'i, Expr<'i, S, X>>,
+    ctx: &Context<&'i str, Expr<'i, S, X>>,
     e: &Expr<'i, S, X>,
 ) -> Result<Expr<'i, S, X>, TypeError<'i, S>>
 where
@@ -773,14 +773,14 @@ pub enum TypeMessage<'i, S> {
 /// A structured type error that includes context
 #[derive(Debug)]
 pub struct TypeError<'i, S> {
-    pub context: Context<'i, Expr<'i, S, X>>,
+    pub context: Context<&'i str, Expr<'i, S, X>>,
     pub current: Expr<'i, S, X>,
     pub type_message: TypeMessage<'i, S>,
 }
 
 impl<'i, S: Clone> TypeError<'i, S> {
     pub fn new(
-        context: &Context<'i, Expr<'i, S, X>>,
+        context: &Context<&'i str, Expr<'i, S, X>>,
         current: &Expr<'i, S, X>,
         type_message: TypeMessage<'i, S>,
     ) -> Self {
diff --git a/dhall_core/src/context.rs b/dhall_core/src/context.rs
index b88a677..412d3f0 100644
--- a/dhall_core/src/context.rs
+++ b/dhall_core/src/context.rs
@@ -1,4 +1,6 @@
+use std::cmp::Eq;
 use std::collections::HashMap;
+use std::hash::Hash;
 
 /// A `(Context a)` associates `Text` labels with values of type `a`
 ///
@@ -13,9 +15,9 @@ use std::collections::HashMap;
 /// `n`th occurrence of a given key.
 ///
 #[derive(Debug, Clone)]
-pub struct Context<'i, T>(HashMap<&'i str, Vec<T>>);
+pub struct Context<K: Eq + Hash, T>(HashMap<K, Vec<T>>);
 
-impl<'i, T> Context<'i, T> {
+impl<K: Hash + Eq + Clone, T> Context<K, T> {
     /// An empty context with no key-value pairs
     pub fn new() -> Self {
         Context(HashMap::new())
@@ -29,23 +31,23 @@ impl<'i, T> Context<'i, T> {
     /// lookup k n (insert k v c) = lookup k (n - 1) c  -- 1 <= n
     /// lookup k n (insert j v c) = lookup k  n      c  -- k /= j
     /// ```
-    pub fn lookup<'a>(&'a self, k: &str, n: usize) -> Option<&'a T> {
-        self.0.get(k).and_then(|v| v.get(v.len() - 1 - n))
+    pub fn lookup<'a>(&'a self, k: K, n: usize) -> Option<&'a T> {
+        self.0.get(&k).and_then(|v| v.get(v.len() - 1 - n))
     }
 
-    pub fn map<U, F: Fn(&T) -> U>(&self, f: F) -> Context<'i, U> {
+    pub fn map<U, F: Fn(&T) -> U>(&self, f: F) -> Context<K, U> {
         Context(
             self.0
                 .iter()
-                .map(|(k, v)| (*k, v.iter().map(&f).collect()))
+                .map(|(k, v)| ((*k).clone(), v.iter().map(&f).collect()))
                 .collect(),
         )
     }
 }
 
-impl<'i, T: Clone> Context<'i, T> {
+impl<K: Hash + Eq + Clone, T: Clone> Context<K, T> {
     /// Add a key-value pair to the `Context`
-    pub fn insert(&self, k: &'i str, v: T) -> Self {
+    pub fn insert(&self, k: K, v: T) -> Self {
         let mut ctx = (*self).clone();
         {
             let m = ctx.0.entry(k).or_insert_with(Vec::new);
diff --git a/dhall_generator/src/lib.rs b/dhall_generator/src/lib.rs
index b316f51..1cc62d0 100644
--- a/dhall_generator/src/lib.rs
+++ b/dhall_generator/src/lib.rs
@@ -4,6 +4,8 @@ use dhall_core::*;
 use proc_macro2::Literal;
 use proc_macro2::TokenStream;
 use quote::quote;
+use std::fmt::Debug;
+use std::hash::Hash;
 
 #[proc_macro]
 pub fn dhall(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
@@ -12,15 +14,15 @@ pub fn dhall(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
     let no_import =
         |_: &Import| -> X { panic!("Don't use import in dhall!()") };
     let expr = expr.map_embed(&no_import);
-    let output = dhall_to_tokenstream(&expr, &Context::new());
+    let output = dhall_to_tokenstream::<&str>(&expr, &Context::new());
     output.into()
 }
 
 // Returns an expression of type Expr<_, _>. Expects input variables
 // to be of type Box<Expr<_, _>> (future-proof for structural sharing).
-fn dhall_to_tokenstream<'i>(
-    expr: &Expr<'i, X, X>,
-    ctx: &Context<'i, ()>,
+fn dhall_to_tokenstream<L: Eq + Hash + Clone + Debug + Into<String>>(
+    expr: &Expr_<L, X, X>,
+    ctx: &Context<L, ()>,
 ) -> TokenStream {
     use dhall_core::Expr_::*;
     match expr {
@@ -30,8 +32,8 @@ fn dhall_to_tokenstream<'i>(
         }
         Lam(x, t, b) => {
             let t = dhall_to_tokenstream_bx(t, ctx);
-            let b = dhall_to_tokenstream_bx(b, &ctx.insert(x, ()));
-            let x = Literal::string(x);
+            let b = dhall_to_tokenstream_bx(b, &ctx.insert(x.clone(), ()));
+            let x = Literal::string(&x.clone().into());
             quote! { Lam(#x, #t, #b) }
         }
         App(f, a) => {
@@ -74,20 +76,22 @@ fn dhall_to_tokenstream<'i>(
 }
 
 // Returns an expression of type Box<Expr<_, _>>
-fn dhall_to_tokenstream_bx<'i>(
-    expr: &Expr<'i, X, X>,
-    ctx: &Context<'i, ()>,
+fn dhall_to_tokenstream_bx<L: Eq + Hash + Clone + Debug + Into<String>>(
+    expr: &Expr_<L, X, X>,
+    ctx: &Context<L, ()>,
 ) -> TokenStream {
     use dhall_core::Expr_::*;
     match expr {
         Var(V(s, n)) => {
-            match ctx.lookup(s, *n) {
+            match ctx.lookup(s.clone(), *n) {
                 // Non-free variable; interpolates as itself
                 Some(()) => {
+                    let s: String = s.clone().into();
                     quote! { bx(Var(V(#s, #n))) }
                 }
                 // Free variable; interpolates as a rust variable
                 None => {
+                    let s: String = s.clone().into();
                     // TODO: insert appropriate shifts ?
                     let v: TokenStream = s.parse().unwrap();
                     quote! { {