From 298c435c3466b36ce83bec90065d7ac2553b4476 Mon Sep 17 00:00:00 2001
From: Eduardo Julian
Date: Thu, 14 Mar 2019 18:13:22 -0400
Subject: Added a peek-and-pop optimization to pattern-matching on JS.

---
 .../lux/tool/compiler/phase/generation/js/case.lux       | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/stdlib/source/lux/tool/compiler/phase/generation/js/case.lux b/stdlib/source/lux/tool/compiler/phase/generation/js/case.lux
index 0bafcd3c0..b8a0cd00d 100644
--- a/stdlib/source/lux/tool/compiler/phase/generation/js/case.lux
+++ b/stdlib/source/lux/tool/compiler/phase/generation/js/case.lux
@@ -69,9 +69,13 @@
   (-> Expression Statement)
   (_.statement (|> @cursor (_.do "push" (list value)))))
 
+(def: peek-and-pop-cursor
+  Expression
+  (|> @cursor (_.do "pop" (list))))
+
 (def: pop-cursor!
   Statement
-  (_.statement (|> @cursor (_.do "pop" (list)))))
+  (_.statement ..peek-and-pop-cursor))
 
 (def: peek-cursor
   Expression
@@ -130,6 +134,16 @@
     ([synthesis.member/left  //runtime.product//left  (<|)]
      [synthesis.member/right //runtime.product//right inc])
 
+    (^ ($_ synthesis.path/seq
+           (#synthesis.Bind register)
+           #synthesis.Pop
+           thenP))
+    (do ////.monad
+      [then! (pattern-matching' generate thenP)]
+      (/////wrap ($_ _.then
+                     (_.define (..register register) ..peek-and-pop-cursor)
+                     then!)))
+
     (^template [<tag> <computation>]
       (^ (<tag> leftP rightP))
       (do ////.monad
-- 
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