From 04c6cd248aff1cbce68ae2fb997705e921d21809 Mon Sep 17 00:00:00 2001
From: Nadrieril
Date: Thu, 4 Apr 2019 18:12:19 +0200
Subject: Tweak matching on Some/None

---
 dhall_core/src/core.rs   | 19 +++++++++++++++++++
 dhall_core/src/parser.rs | 30 +++++++++---------------------
 2 files changed, 28 insertions(+), 21 deletions(-)

(limited to 'dhall_core')

diff --git a/dhall_core/src/core.rs b/dhall_core/src/core.rs
index 0ea8c83..afa3d3f 100644
--- a/dhall_core/src/core.rs
+++ b/dhall_core/src/core.rs
@@ -324,6 +324,25 @@ pub fn rc<T>(x: T) -> Rc<T> {
     Rc::new(x)
 }
 
+pub fn app<N, E>(f: Expr<N, E>, args: Vec<SubExpr<N, E>>) -> Expr<N, E> {
+    if args.is_empty() {
+        f
+    } else {
+        Expr::App(rc(f), args)
+    }
+}
+
+pub fn app_rc<N, E>(
+    f: SubExpr<N, E>,
+    args: Vec<SubExpr<N, E>>,
+) -> SubExpr<N, E> {
+    if args.is_empty() {
+        f
+    } else {
+        rc(Expr::App(f, args))
+    }
+}
+
 fn add_ui(u: usize, i: isize) -> usize {
     if i < 0 {
         u.checked_sub(i.checked_neg().unwrap() as usize).unwrap()
diff --git a/dhall_core/src/parser.rs b/dhall_core/src/parser.rs
index a0e4397..68796c4 100644
--- a/dhall_core/src/parser.rs
+++ b/dhall_core/src/parser.rs
@@ -700,28 +700,16 @@ make_parser! {
 
     rule!(application_expression<ParsedExpr> as expression; children!(
         [expression(e)] => e,
-        [expression(first), expression(second)] => {
-            match first {
-                Expr::Builtin(Builtin::OptionalNone) =>
-                    Expr::EmptyOptionalLit(rc(second)),
-                Expr::Builtin(Builtin::OptionalSome) =>
-                    Expr::NEOptionalLit(rc(second)),
-                _ => Expr::App(rc(first), vec![rc(second)]),
-            }
+        [expression(Expr::Builtin(Builtin::OptionalNone)),
+                expression(e), expression(rest)..] => {
+            app(Expr::EmptyOptionalLit(rc(e)), rest.map(rc).collect())
         },
-        [expression(first), expression(second), expression(rest)..] => {
-            match first {
-                Expr::Builtin(Builtin::OptionalNone) =>
-                    Expr::App(rc(Expr::EmptyOptionalLit(rc(second))),
-                                 rest.map(rc).collect()),
-                Expr::Builtin(Builtin::OptionalSome) =>
-                    Expr::App(rc(Expr::NEOptionalLit(rc(second))),
-                                 rest.map(rc).collect()),
-                _ => Expr::App(rc(first),
-                                  std::iter::once(rc(second))
-                                    .chain(rest.map(rc))
-                                    .collect()),
-            }
+        [expression(Expr::Builtin(Builtin::OptionalSome)),
+                expression(e), expression(rest)..] => {
+            app(Expr::NEOptionalLit(rc(e)), rest.map(rc).collect())
+        },
+        [expression(first), expression(rest)..] => {
+            app(first, rest.map(rc).collect())
         },
     ));
 
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