From e3cdf3f386b6a682981e6bdf6ca6d215b0d0788d Mon Sep 17 00:00:00 2001
From: Nadrieril
Date: Thu, 25 Jun 2020 14:06:24 +0100
Subject: spec: not all ABNF parsers like empty rules

---
 dhall/src/syntax/text/dhall.abnf | 20 +++++++-------------
 1 file changed, 7 insertions(+), 13 deletions(-)

(limited to 'dhall/src/syntax/text/dhall.abnf')

diff --git a/dhall/src/syntax/text/dhall.abnf b/dhall/src/syntax/text/dhall.abnf
index 05d76e6..362a436 100644
--- a/dhall/src/syntax/text/dhall.abnf
+++ b/dhall/src/syntax/text/dhall.abnf
@@ -896,11 +896,9 @@ primitive-expression =
 
 record-type-or-literal =
       empty-record-literal
-    / non-empty-record-type-or-literal
-    / empty-record-type
+    / [non-empty-record-type-or-literal]
 
 empty-record-literal = "="
-empty-record-type = ""
 
 non-empty-record-type-or-literal =
     (non-empty-record-type / non-empty-record-literal)
@@ -913,22 +911,18 @@ record-type-entry = any-label-or-some whsp ":" whsp1 expression
 non-empty-record-literal =
     record-literal-entry *(whsp "," whsp record-literal-entry)
 
+; If the `record-literal-normal-entry` is absent, that represents a punned
+; record entry, such as in `{ x }`, which is a short-hand for `{ x = x }`
 record-literal-entry =
-    any-label-or-some (record-literal-normal-entry / record-literal-punned-entry)
+    any-label-or-some [record-literal-normal-entry]
 
 record-literal-normal-entry =
     *(whsp "." whsp any-label-or-some) whsp "=" whsp expression
-record-literal-punned-entry = ""
-
 
+; If the `union-type-entry` is absent, that represents an empty union
+; alternative, such as in `< Heads | Tails >`
 union-type =
-      non-empty-union-type
-    / empty-union-type
-
-empty-union-type = ""
-
-non-empty-union-type =
-    union-type-entry *(whsp "|" whsp union-type-entry)
+    [union-type-entry *(whsp "|" whsp union-type-entry)]
 
 ; x : Natural
 ; x
-- 
cgit v1.2.3