Disallow builtins as bound variables

1 files changed, 12 insertions, 4 deletions

diff --git a/dhall_core/src/parser.rs b/dhall_core/src/parser.rs
index 3f53c49..4f26b0f 100644
--- a/dhall_core/src/parser.rs
+++ b/dhall_core/src/parser.rs
@@ -266,6 +266,14 @@ make_parser! {
         [simple_label(l)] => l,
         [quoted_label(l)] => l,
     ));
+    rule!(unreserved_label<Label>; children!(
+        [label(l)] => {
+            if Builtin::parse(&String::from(&l)).is_some() {
+                Err(format!("Builtin names are not allowed as bound variables"))?
+            }
+            l
+        },
+    ));
 
     rule!(double_quote_literal<ParsedText>; children!(
         [double_quote_chunk(chunks..)] => {
@@ -493,7 +501,7 @@ make_parser! {
     ));
 
     rule!(lambda_expression<ParsedExpr> as expression; children!(
-        [label(l), expression(typ), expression(body)] => {
+        [unreserved_label(l), expression(typ), expression(body)] => {
             bx(Expr::Lam(l, typ, body))
         }
     ));
@@ -511,12 +519,12 @@ make_parser! {
     ));
 
     rule!(let_binding<(Label, Option<ParsedExpr>, ParsedExpr)>; children!(
-        [label(name), expression(annot), expression(expr)] => (name, Some(annot), expr),
-        [label(name), expression(expr)] => (name, None, expr),
+        [unreserved_label(name), expression(annot), expression(expr)] => (name, Some(annot), expr),
+        [unreserved_label(name), expression(expr)] => (name, None, expr),
     ));
 
     rule!(forall_expression<ParsedExpr> as expression; children!(
-        [label(l), expression(typ), expression(body)] => {
+        [unreserved_label(l), expression(typ), expression(body)] => {
             bx(Expr::Pi(l, typ, body))
         }
     ));