From 375013f9ea4857f46effc4d4a8c2a68956cb3184 Mon Sep 17 00:00:00 2001
From: Christopher Lam <christopher.lck@gmail.com>
Date: Sat, 20 Apr 2019 14:11:03 +0800
Subject: [PATCH] [commodity-utils] simplify gnc:make-exchange-function

Remove assigning exchangelist to exchange-alist.

Removes need to test foreign-amount against 0 - multiplication will
result in 0 anyway. The only functional change is the condition
whereby foreign's commodity is not present in exchangelist; previously
it would return (gnc:make-gnc-monetary domestic 0); now it returns #f.

This function *is* allowed to return #f for invalid or missing prices;
see the (and foreign ...) conditional.
---
 .../report-system/commodity-utilities.scm     | 29 ++++++++-----------
 1 file changed, 12 insertions(+), 17 deletions(-)

diff --git a/gnucash/report/report-system/commodity-utilities.scm b/gnucash/report/report-system/commodity-utilities.scm
index b4c73a116e..a0877a1c59 100644
--- a/gnucash/report/report-system/commodity-utilities.scm
+++ b/gnucash/report/report-system/commodity-utilities.scm
@@ -690,23 +690,18 @@ construct with gnc:make-gnc-monetary and gnc:monetary->string instead.")
 ;; the <gnc:commodity*> domestic-commodity, exchanges the amount into
 ;; the domestic currency and returns a <gnc-monetary>.
 (define (gnc:make-exchange-function exchange-alist)
-  (let ((exchangelist exchange-alist))
-    (lambda (foreign domestic)
-      (gnc:debug "foreign: " (gnc:monetary->string foreign))
-      (gnc:debug "domestic: " (gnc-commodity-get-printname domestic))
-      (and foreign
-           (or (gnc:exchange-by-euro foreign domestic #f)
-               (gnc:exchange-if-same foreign domestic)
-               (gnc:make-gnc-monetary
-                domestic
-                (let ((pair (assoc (gnc:gnc-monetary-commodity foreign)
-                                   exchangelist))
-                      (foreign-amount (gnc:gnc-monetary-amount foreign)))
-                  (if (or (not pair)
-                          (zero? foreign-amount))
-                      0
-                      (* foreign-amount
-                         (cadr pair))))))))))
+  (lambda (foreign domestic)
+    (gnc:debug "foreign: " (gnc:monetary->string foreign))
+    (gnc:debug "domestic: " (gnc-commodity-get-printname domestic))
+    (and foreign
+         (or (gnc:exchange-by-euro foreign domestic #f)
+             (gnc:exchange-if-same foreign domestic)
+             (let* ((foreign-comm (gnc:gnc-monetary-commodity foreign))
+                    (pair (assoc foreign-comm exchange-alist)))
+               (and pair
+                    (gnc:make-gnc-monetary
+                     domestic
+                     (* (gnc:gnc-monetary-amount foreign) (cadr pair)))))))))
 
 ;; Helper for the gnc:exchange-by-pricalist* below. Exchange the
 ;; <gnc:monetary> 'foreign' into the <gnc:commodity*> 'domestic' by