2 files changed, 30 insertions, 17 deletions
diff --git a/dhall_core/src/parser.rs b/dhall_core/src/parser.rs
index 60ab6ef..c569918 100644
--- a/dhall_core/src/parser.rs
+++ b/dhall_core/src/parser.rs
@@ -841,29 +841,41 @@ make_parser! {
     rule!(non_empty_union_type_or_literal
           <(Option<(Label, ParsedSubExpr)>, BTreeMap<Label, ParsedSubExpr>)>;
             children!(
-        [label(l), expression(e), union_type_entries(entries)] => {
+        [label(l), union_literal_variant_value((e, entries))] => {
             (Option::Some((l, rc(e))), entries)
         },
-        [label(l), expression(e), non_empty_union_type_or_literal(rest)] => {
+        [label(l), union_type_or_literal_variant_type((e, rest))] => {
             let (x, mut entries) = rest;
             entries.insert(l, rc(e));
             (x, entries)
         },
-        [label(l), expression(e)] => {
-            let mut entries = BTreeMap::new();
-            entries.insert(l, rc(e));
-            (Option::None, entries)
-        },
     ));
 
-    rule!(union_type_entries<BTreeMap<Label, ParsedSubExpr>>; children!(
-        [union_type_entry(entries)..] => entries.collect()
+    rule!(union_literal_variant_value
+          <(ParsedExpr, BTreeMap<Label, ParsedSubExpr>)>;
+            children!(
+        [expression(e), union_type_entry(entries)..] => {
+            (e, entries.collect())
+        },
     ));
 
     rule!(union_type_entry<(Label, ParsedSubExpr)>; children!(
         [label(name), expression(expr)] => (name, rc(expr))
     ));
 
+    // TODO: unary union variants
+    rule!(union_type_or_literal_variant_type
+          <(ParsedExpr,
+            (Option<(Label, ParsedSubExpr)>, BTreeMap<Label, ParsedSubExpr>))>;
+                children!(
+        [expression(e), non_empty_union_type_or_literal(rest)] => {
+            (e, rest)
+        },
+        [expression(e)] => {
+            (e, (Option::None, BTreeMap::new()))
+        },
+    ));
+
     rule!(non_empty_list_literal<ParsedExpr> as expression; children!(
         [expression(items)..] => Expr::NEListLit(items.map(rc).collect())
     ));
diff --git a/dhall_parser/src/dhall.abnf b/dhall_parser/src/dhall.abnf
index 01ec6d8..7ad0b24 100644
--- a/dhall_parser/src/dhall.abnf
+++ b/dhall_parser/src/dhall.abnf
@@ -688,17 +688,18 @@ union-type-or-literal =
 empty-union-type = ""
 
 non-empty-union-type-or-literal =
-    any-label whsp
-    ( "=" whsp expression union-type-entries
-    / ":" whsp1 expression [ whsp "|" whsp non-empty-union-type-or-literal ]
-    )
-union-type-entries = *(whsp "|" whsp union-type-entry)
+    any-label [ whsp ( union-literal-variant-value / union-type-or-literal-variant-type) ]
+
+; = True | ...
+union-literal-variant-value = "=" whsp expression *(whsp "|" whsp union-type-entry)
 union-type-entry = any-label whsp ":" whsp1 expression
 
-; "[1, 2, 3]"
-; `empty-list-or-optional` handles empty lists
-non-empty-list-literal = "[" whsp expression whsp *("," whsp expression whsp) "]"
+; : Integer | ...
+; | ...
+union-type-or-literal-variant-type = [ ":" whsp1 expression ] [ whsp "|" whsp non-empty-union-type-or-literal ]
 
 
+non-empty-list-literal = "[" whsp expression whsp *("," whsp expression whsp) "]"
+
 ; This just adds surrounding whitespace for the top-level of the program
 complete-expression = whsp expression whsp