Handle empty optionals correctly

Closes #78

4 files changed, 18 insertions, 6 deletions

diff --git a/dhall_core/src/core.rs b/dhall_core/src/core.rs
index 7859c73..c0e04ed 100644
--- a/dhall_core/src/core.rs
+++ b/dhall_core/src/core.rs
@@ -174,6 +174,10 @@ pub enum ExprF<SubExpr, Label, Note, Embed> {
     EmptyListLit(SubExpr),
     ///  [x, y, z]
     NEListLit(Vec<SubExpr>),
+    /// Deprecated Optional literal form
+    ///  [] : Optional a
+    ///  [x] : Optional a
+    OldOptionalLit(Option<SubExpr>, SubExpr),
     ///  None t
     EmptyOptionalLit(SubExpr),
     ///  Some e
diff --git a/dhall_core/src/parser.rs b/dhall_core/src/parser.rs
index cea7cea..c4ae2e5 100644
--- a/dhall_core/src/parser.rs
+++ b/dhall_core/src/parser.rs
@@ -641,13 +641,13 @@ make_parser! {
             spanned(span, EmptyListLit(rc(t)))
         },
         [Optional(_), expression(t)] => {
-            spanned(span, EmptyOptionalLit(rc(t)))
+            spanned(span, OldOptionalLit(None, rc(t)))
         },
     ));
 
     rule!(non_empty_optional<ParsedExpr<'a>> as expression; span; children!(
         [expression(x), Optional(_), expression(t)] => {
-            spanned(span, Annot(rc(NEOptionalLit(rc(x))), rc(t)))
+            spanned(span, OldOptionalLit(Option::Some(rc(x)), rc(t)))
         }
     ));
 
@@ -747,10 +747,6 @@ make_parser! {
 
     rule!(application_expression<ParsedExpr<'a>> as expression; span; children!(
         [expression(e)] => e,
-        [expression(Builtin(crate::Builtin::OptionalNone)),
-                expression(e), expression(rest)..] => {
-            spanned(span, app(EmptyOptionalLit(rc(e)), rest.map(rc).collect()))
-        },
         [Some(()), expression(e), expression(rest)..] => {
             spanned(span, app(NEOptionalLit(rc(e)), rest.map(rc).collect()))
         },
diff --git a/dhall_core/src/printer.rs b/dhall_core/src/printer.rs
index e53c1ec..bb094de 100644
--- a/dhall_core/src/printer.rs
+++ b/dhall_core/src/printer.rs
@@ -32,6 +32,12 @@ impl<SE: Display + Clone, N, E: Display> Display for ExprF<SE, Label, N, E> {
             NEListLit(es) => {
                 fmt_list("[", ", ", "]", es, f, Display::fmt)?;
             }
+            OldOptionalLit(None, t) => {
+                write!(f, "[] : Optional {}", t)?;
+            }
+            OldOptionalLit(Some(x), t) => {
+                write!(f, "[{}] : Optional {}", x, t)?;
+            }
             EmptyOptionalLit(t) => {
                 write!(f, "None {}", t)?;
             }
@@ -149,6 +155,7 @@ impl<S: Clone, A: Display + Clone> Expr<S, A> {
             | Let(_, _, _, _)
             | EmptyListLit(_)
             | NEListLit(_)
+            | OldOptionalLit(_, _)
             | EmptyOptionalLit(_)
             | NEOptionalLit(_)
             | Merge(_, _, _)
@@ -189,6 +196,7 @@ impl<S: Clone, A: Display + Clone> Expr<S, A> {
                 b.phase(PrintPhase::BinOp(op)),
             ),
             EmptyListLit(t) => EmptyListLit(t.phase(Import)),
+            OldOptionalLit(x, t) => OldOptionalLit(x, t.phase(Import)),
             EmptyOptionalLit(t) => EmptyOptionalLit(t.phase(Import)),
             NEOptionalLit(e) => NEOptionalLit(e.phase(Import)),
             ExprF::App(a, args) => ExprF::App(
diff --git a/dhall_core/src/visitor.rs b/dhall_core/src/visitor.rs
index b0424ac..3b06f8b 100644
--- a/dhall_core/src/visitor.rs
+++ b/dhall_core/src/visitor.rs
@@ -148,6 +148,10 @@ where
             ),
             EmptyListLit(t) => EmptyListLit(v.visit_subexpr(t)?),
             NEListLit(es) => NEListLit(vec(es, |e| v.visit_subexpr(e))?),
+            OldOptionalLit(x, t) => OldOptionalLit(
+                opt(x, |e| v.visit_subexpr(e))?,
+                v.visit_subexpr(t)?,
+            ),
             EmptyOptionalLit(t) => EmptyOptionalLit(v.visit_subexpr(t)?),
             NEOptionalLit(e) => NEOptionalLit(v.visit_subexpr(e)?),
             RecordType(kts) => RecordType(btmap(kts, v)?),