From 70568c910982930a160a24a0d6d3ebde2484be32 Mon Sep 17 00:00:00 2001
From: Eduardo Julian
Date: Wed, 1 May 2019 21:53:54 -0400
Subject: Turned "sum//get" into an iterative loop.

---
 stdlib/source/lux/target/common-lisp.lux           |  5 +++
 .../phase/generation/common-lisp/runtime.lux       | 49 ++++++++++++----------
 2 files changed, 33 insertions(+), 21 deletions(-)

diff --git a/stdlib/source/lux/target/common-lisp.lux b/stdlib/source/lux/target/common-lisp.lux
index ad3d9be8f..dc8694dc9 100644
--- a/stdlib/source/lux/target/common-lisp.lux
+++ b/stdlib/source/lux/target/common-lisp.lux
@@ -420,3 +420,8 @@
                (:transmutation else)
                (list.reverse clauses)))
   )
+
+(def: #export (while condition body)
+  (-> (Expression Any) (Expression Any) (Computation Any))
+  (..form (list (..var "loop") (..var "while") condition
+                (..var "do") body)))
diff --git a/stdlib/source/lux/tool/compiler/phase/generation/common-lisp/runtime.lux b/stdlib/source/lux/tool/compiler/phase/generation/common-lisp/runtime.lux
index 87fc7741d..774844bdf 100644
--- a/stdlib/source/lux/tool/compiler/phase/generation/common-lisp/runtime.lux
+++ b/stdlib/source/lux/tool/compiler/phase/generation/common-lisp/runtime.lux
@@ -182,27 +182,34 @@
 ## TODO: Find a way to extract parts of the sum without "nth", which
 ## does a linear search, and is thus expensive.
 (runtime: (sum//get sum wantsLast wantedTag)
-  (let [no-match! sum
-        sum-tag (_.nth/2 [(_.int +0) sum])
-        sum-flag (_.nth/2 [(_.int +1) sum])
-        sum-value (_.nth/2 [(_.int +2) sum])
-        test-recursion! (_.if sum-flag
-                          ## Must recurse.
-                          (sum//get sum-value wantsLast (_.- sum-tag wantedTag))
-                          no-match!)]
-    (_.cond (list [(_.= sum-tag wantedTag)
-                   (_.if (_.equal wantsLast sum-flag)
-                     sum-value
-                     test-recursion!)]
-
-                  [(_.> sum-tag wantedTag)
-                   test-recursion!]
-
-                  [(_.and (_.< sum-tag wantedTag)
-                          wantsLast)
-                   (variant' (_.- wantedTag sum-tag) sum-flag sum-value)])
-
-            no-match!)))
+  (with-vars [sum-tag sum-flag]
+    (let [@exit (_.label "exit")
+          return! (_.return-from @exit)
+          no-match! (return! sum)
+          sum-value (_.nth/2 [(_.int +2) sum])
+          test-recursion! (_.if sum-flag
+                            ## Must iterate.
+                            ($_ _.progn
+                                (_.setq sum sum-value)
+                                (_.setq wantedTag (_.- sum-tag wantedTag)))
+                            no-match!)]
+      (<| (_.progn (_.setq sum-tag (_.nth/2 [(_.int +0) sum])))
+          (_.progn (_.setq sum-flag (_.nth/2 [(_.int +1) sum])))
+          (_.block @exit)
+          (_.while (_.bool true))
+          (_.cond (list [(_.= sum-tag wantedTag)
+                         (_.if (_.equal wantsLast sum-flag)
+                           (return! sum-value)
+                           test-recursion!)]
+
+                        [(_.> sum-tag wantedTag)
+                         test-recursion!]
+
+                        [(_.and (_.< sum-tag wantedTag)
+                                wantsLast)
+                         (return! (variant' (_.- wantedTag sum-tag) sum-flag sum-value))])
+
+                  no-match!)))))
 
 (def: runtime//adt
   ($_ _.progn
-- 
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