From 0c9c9c2594569bed8867eeff55bb1ab6ca76bf1e Mon Sep 17 00:00:00 2001
From: Christopher Lam <christopher.lck@gmail.com>
Date: Thu, 19 Sep 2019 21:43:44 +0800
Subject: [PATCH 01/14] [test-trial-balance] augment to test unrealized gains

these were already tested -- see previous tests *do* include
'unrealized losses'. augment by adding another couple foreign transfer
to change the unrealized gain/loss amount.
---
 .../test/test-trial-balance.scm               | 20 ++++++++++++++++---
 1 file changed, 17 insertions(+), 3 deletions(-)

diff --git a/gnucash/report/standard-reports/test/test-trial-balance.scm b/gnucash/report/standard-reports/test/test-trial-balance.scm
index d343fe2e76..43d8be638b 100644
--- a/gnucash/report/standard-reports/test/test-trial-balance.scm
+++ b/gnucash/report/standard-reports/test/test-trial-balance.scm
@@ -62,13 +62,15 @@
 (define (test-trial-balance)
   (let* ((options (gnc:make-report-options uuid))
          (account-alist (create-test-data))
+         (gbp-bank (assoc-ref account-alist "GBP Bank"))
+         (usd-bank (assoc-ref account-alist "Bank"))
          (expense (assoc-ref account-alist "Expenses"))
          (equity (assoc-ref account-alist "Equity"))
          (income (assoc-ref account-alist "Income"))
          (bank (assoc-ref account-alist "Bank")))
 
     (gnc-commodity-set-user-symbol
-     (xaccAccountGetCommodity (assoc-ref account-alist "GBP Bank"))
+     (xaccAccountGetCommodity gbp-bank)
      "#")
 
     (let ((closing-txn (env-transfer #f 30 06 2003 expense equity
@@ -167,6 +169,18 @@
         (sxml->table-row-col sxml 1 #f 10))
 
       (test-equal "work-sheet bs credits"
-        ' ("$3.00" "$2,356.00" "$2,359.00" "$760.00" "$3,119.00")
+        '("$3.00" "$2,356.00" "$2,359.00" "$760.00" "$3,119.00")
         (sxml->table-row-col sxml 1 #f 11)))
-    ))
+
+    ;; A couple of transactions which involve foreign currency
+    ;; conversions. We'll set the currencies to GBP and USD.
+    (env-transfer-foreign #f 15 01 2000 gbp-bank usd-bank
+                          10 14 #:description "GBP 10 to USD 14")
+    (env-transfer-foreign #f 15 02 2000 usd-bank gbp-bank
+                          9  8 #:description "USD 9 to GBP 8")
+
+    (set-option options "General" "Report variation" 'current)
+    (let ((sxml (options->sxml options "test-unrealized-gain")))
+      (test-equal "unrealized losses"
+        '("Unrealized Gains" "$3.25")
+        (sxml->table-row-col sxml 1 -2 #f)))))

From f88c54bb50a8527067225ea3586331238844ad79 Mon Sep 17 00:00:00 2001
From: Christopher Lam <christopher.lck@gmail.com>
Date: Thu, 19 Sep 2019 21:07:01 +0800
Subject: [PATCH 02/14] [trial-balance] use gnc:commodity-collector-get-negated

---
 gnucash/report/standard-reports/trial-balance.scm | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/gnucash/report/standard-reports/trial-balance.scm b/gnucash/report/standard-reports/trial-balance.scm
index 8b8aed9d5b..35aa425a18 100644
--- a/gnucash/report/standard-reports/trial-balance.scm
+++ b/gnucash/report/standard-reports/trial-balance.scm
@@ -152,9 +152,7 @@
          (amt (and sum (gnc:gnc-monetary-amount sum)))
          (neg? (and amt (negative? amt)))
          (bal (if neg?
-                  (let ((bal (gnc:make-commodity-collector)))
-                    (bal 'minusmerge signed-balance #f)
-                    bal)
+                  (gnc:commodity-collector-get-negated signed-balance)
                   signed-balance))
          (bal-sum (gnc:sum-collector-commodity
                    bal

From acf359a7973aa30686529ce46d18617ac51d77f8 Mon Sep 17 00:00:00 2001
From: Christopher Lam <christopher.lck@gmail.com>
Date: Thu, 19 Sep 2019 21:07:41 +0800
Subject: [PATCH 03/14] [trial-balance] upgrade coll-plus and coll-minus to
 report-wide fns

---
 .../report/standard-reports/trial-balance.scm | 19 +++++++++++++------
 1 file changed, 13 insertions(+), 6 deletions(-)

diff --git a/gnucash/report/standard-reports/trial-balance.scm b/gnucash/report/standard-reports/trial-balance.scm
index 35aa425a18..49a4ba4855 100644
--- a/gnucash/report/standard-reports/trial-balance.scm
+++ b/gnucash/report/standard-reports/trial-balance.scm
@@ -316,6 +316,19 @@
 
     options))
 
+;; (coll-plus collectors ...) equiv to (+ collectors ...)
+(define (coll-plus . collectors)
+  (let ((res (gnc:make-commodity-collector)))
+    (for-each (lambda (coll) (res 'merge coll #f)) collectors)
+    res))
+
+;; (coll-minus collectors ...) equiv to (- collector0 collector1 ...)
+(define (coll-minus . collectors)
+  (let ((res (gnc:make-commodity-collector)))
+    (res 'merge (car collectors) #f)
+    (for-each (lambda (coll) (res 'minusmerge coll #f)) (cdr collectors))
+    res))
+
   ;;;;;;;;;;;;;;;;;;;;;;;;;;;
 ;; trial-balance-renderer
 ;; set up the document and add the table
@@ -665,12 +678,6 @@
                  splits)
                 total))
 
-            (define (coll-minus . collectors)
-              (let ((res (gnc:make-commodity-collector)))
-                (res 'merge (car collectors) #f)
-                (for-each (lambda (mon) (res 'minusmerge mon #f)) (cdr collectors))
-                res))
-
             (while (< row rows)
               (let* ((env (gnc:html-acct-table-get-row-env acct-table row))
                      (acct (get-val env 'account))

From 6b573de128c6509bb447db0020849cbde764b457 Mon Sep 17 00:00:00 2001
From: Christopher Lam <christopher.lck@gmail.com>
Date: Thu, 19 Sep 2019 21:07:58 +0800
Subject: [PATCH 04/14] [trial-balance] use coll-plus and coll-minus for
 functional style

---
 .../report/standard-reports/trial-balance.scm | 28 +++++++------------
 1 file changed, 10 insertions(+), 18 deletions(-)

diff --git a/gnucash/report/standard-reports/trial-balance.scm b/gnucash/report/standard-reports/trial-balance.scm
index 49a4ba4855..9a9cc89749 100644
--- a/gnucash/report/standard-reports/trial-balance.scm
+++ b/gnucash/report/standard-reports/trial-balance.scm
@@ -692,18 +692,14 @@
                       (and ga-or-is? (coll-minus adjusting pos-adjusting)))
                      (pre-closing-bal (coll-minus curr-bal closing))
                      (pre-adjusting-bal (coll-minus pre-closing-bal adjusting))
-                     (atb (if is?
-                              (let* ((debit (gnc:make-commodity-collector))
-                                     (credit (gnc:make-commodity-collector)))
-                                (debit 'merge pos-adjusting #f)
-                                (credit 'merge neg-adjusting #f)
-                                (if (double-col
-                                     'credit-q pre-adjusting-bal
-                                     report-commodity exchange-fn show-fcur?)
-                                    (credit 'merge pre-adjusting-bal #f)
-                                    (debit 'merge pre-adjusting-bal #f))
-                                (list debit credit))
-                              pre-closing-bal)))
+                     (atb (cond ((not is?) pre-closing-bal)
+                                ((double-col 'credit-q pre-adjusting-bal
+                                             report-commodity exchange-fn show-fcur?)
+                                 (list (coll-plus pos-adjusting)
+                                       (coll-plus neg-adjusting pre-adjusting-bal)))
+                                (else
+                                 (list (coll-plus pos-adjusting pre-adjusting-bal)
+                                       (coll-plus neg-adjusting))))))
 
                 ;; curr-bal = account-bal with closing & adj entries
                 ;; pre-closing-bal = account-bal with adj entries only
@@ -870,8 +866,8 @@
                  (tot-abs-amt-cell bs-credits))
                 '())))
           (if (eq? report-variant 'work-sheet)
-              (let* ((net-is (gnc:make-commodity-collector))
-                     (net-bs (gnc:make-commodity-collector))
+              (let* ((net-is (coll-minus is-debits is-credits))
+                     (net-bs (coll-minus bs-debits bs-credits))
                      (tot-is (gnc:make-commodity-collector))
                      (tot-bs (gnc:make-commodity-collector))
                      (is-entry #f)
@@ -880,10 +876,6 @@
                      (bs-credit? #f)
                      (tbl-width (+ account-cols (* 2 bs-col) 2))
                      (this-row (gnc:html-table-num-rows build-table)))
-                (net-is 'merge is-debits #f)
-                (net-is 'minusmerge is-credits #f)
-                (net-bs 'merge bs-debits #f)
-                (net-bs 'minusmerge bs-credits #f)
                 (set! is-entry
                   (double-col 'entry net-is report-commodity exchange-fn show-fcur?))
                 (set! is-credit?

From 656d2718d8e570f6eb21e1ad29b0f7ea8cdd652f Mon Sep 17 00:00:00 2001
From: Christopher Lam <christopher.lck@gmail.com>
Date: Thu, 19 Sep 2019 21:21:35 +0800
Subject: [PATCH 05/14] [trial-balance] compact (collect-unrealized-gains)

use functional style
---
 .../report/standard-reports/trial-balance.scm | 39 ++++++-------------
 1 file changed, 12 insertions(+), 27 deletions(-)

diff --git a/gnucash/report/standard-reports/trial-balance.scm b/gnucash/report/standard-reports/trial-balance.scm
index 9a9cc89749..fd726ee71d 100644
--- a/gnucash/report/standard-reports/trial-balance.scm
+++ b/gnucash/report/standard-reports/trial-balance.scm
@@ -523,36 +523,21 @@
           ;;
           ;; This procedure returns a commodity collector.
           (define (collect-unrealized-gains)
+            (define (acct->bal acct)
+              (gnc:account-get-comm-balance-at-date acct end-date #f))
             (if (eq? price-source 'average-cost)
                 ;; No need to calculate if doing valuation at cost.
                 (gnc:make-commodity-collector)
-                (let ((book-balance (gnc:make-commodity-collector))
-                      (unrealized-gain-collector (gnc:make-commodity-collector))
-                      (cost-fn (gnc:case-exchange-fn
-                                'average-cost report-commodity end-date)))
-
-                  ;; Calculate book balance.
-                  ;; assets - liabilities - equity; normally 0
-                  (for-each
-                   (lambda (acct)
-                     (book-balance
-                      'merge
-                      (gnc:account-get-comm-balance-at-date acct end-date #f)
-                      #f))
-                   all-accounts)
-
-                  (let ((value (gnc:gnc-monetary-amount
-                                (gnc:sum-collector-commodity
-                                 book-balance report-commodity exchange-fn)))
-                        (cost (gnc:gnc-monetary-amount
-                               (gnc:sum-collector-commodity
-                                book-balance report-commodity cost-fn))))
-
-                    ;; Get the unrealized gain or loss (value minus cost).
-                    (unrealized-gain-collector
-                     'add report-commodity (- value cost))
-                    unrealized-gain-collector))))
-
+                (let* ((cost-fn (gnc:case-exchange-fn
+                                 'average-cost report-commodity end-date))
+                       (acct-balances (map acct->bal all-accounts))
+                       (book-balance (apply coll-plus acct-balances))
+                       (value (gnc:sum-collector-commodity
+                               book-balance report-commodity exchange-fn))
+                       (cost (gnc:sum-collector-commodity
+                              book-balance report-commodity cost-fn)))
+                  ;; Get the unrealized gain or loss (value minus cost).
+                  (gnc:monetaries-add value (gnc:monetary-neg cost)))))
 
           ;; set default cell alignment
           (gnc:html-table-set-style!

From 0ab0d23b00a674bb655e1d67cb3eb8f5055f7e06 Mon Sep 17 00:00:00 2001
From: Christopher Lam <christopher.lck@gmail.com>
Date: Fri, 20 Sep 2019 11:12:37 +0800
Subject: [PATCH 06/14] Bug 797418 - In budget report, column with Actual
 Totals for Liabilities and Income are reversed

budget.scm had some cleanup whereby totals were accumulated but are
now re-retrieved. Forgot to reverse actuals for some account signs
reversals.
---
 gnucash/report/standard-reports/budget.scm | 1 +
 1 file changed, 1 insertion(+)

diff --git a/gnucash/report/standard-reports/budget.scm b/gnucash/report/standard-reports/budget.scm
index 5a994d6d82..a13b566772 100644
--- a/gnucash/report/standard-reports/budget.scm
+++ b/gnucash/report/standard-reports/budget.scm
@@ -396,6 +396,7 @@
                                budget acct total-periods))
                    (act-total (gnc:get-account-periodlist-actual-value
                                budget acct total-periods))
+                   (act-total (if reverse-balance? (- act-total) act-total))
                    (dif-total (if income-acct?
                                   (- act-total bgt-total)
                                   (- bgt-total act-total))))

From 49372e76be61ac4eae479fee645b183a834ad43e Mon Sep 17 00:00:00 2001
From: Christopher Lam <christopher.lck@gmail.com>
Date: Fri, 20 Sep 2019 09:04:34 +0800
Subject: [PATCH 07/14] Ensure book returns current-book

fixes https://lists.gnucash.org/pipermail/gnucash-user/2019-September/086967.html

because occasionally account will be null or #f, causing error when
passed to gnc-account-get-book.
---
 gnucash/report/business-reports/owner-report.scm   | 4 ++--
 gnucash/report/locale-specific/us/taxtxf-de_DE.scm | 6 +-----
 2 files changed, 3 insertions(+), 7 deletions(-)

diff --git a/gnucash/report/business-reports/owner-report.scm b/gnucash/report/business-reports/owner-report.scm
index d71664229a..6c956d5df7 100644
--- a/gnucash/report/business-reports/owner-report.scm
+++ b/gnucash/report/business-reports/owner-report.scm
@@ -748,8 +748,8 @@
      (end-date (gnc:time64-end-day-time 
                (gnc:date-option-absolute-time
                (opt-val gnc:pagename-general optname-to-date))))
-     (book (gnc-account-get-book account))
-     (date-format (if (not (null? book)) (gnc:options-fancy-date book)))
+     (book (gnc-get-current-book))
+     (date-format (gnc:options-fancy-date book))
      (type (opt-val "__reg" "owner-type"))
      (owner-descr (owner-string type))
      (date-type (opt-val gnc:pagename-general optname-date-driver))
diff --git a/gnucash/report/locale-specific/us/taxtxf-de_DE.scm b/gnucash/report/locale-specific/us/taxtxf-de_DE.scm
index f0a0ab85c1..6557dd0f1c 100644
--- a/gnucash/report/locale-specific/us/taxtxf-de_DE.scm
+++ b/gnucash/report/locale-specific/us/taxtxf-de_DE.scm
@@ -505,11 +505,7 @@
                                 (validate (reverse 
                                            (gnc-account-get-children-sorted
                                             (gnc-get-current-root-account))))))
-         (book (if selected-accounts
-                   (gnc-account-get-book (if (pair? selected-accounts)
-                                             (car selected-accounts)
-                                             selected-accounts))
-                   #f))
+         (book (gnc-get-current-book))
          (generations (if (pair? selected-accounts)
                           (apply max (map (lambda (x) (num-generations x 1))
                                           selected-accounts))

From 3208879e64ea0d692d626cbc9052e6ea590f3ad3 Mon Sep 17 00:00:00 2001
From: Christopher Lam <christopher.lck@gmail.com>
Date: Fri, 20 Sep 2019 10:16:17 +0800
Subject: [PATCH 08/14] [app-utils] upgrade Tax/Tax Number option to all
 locales

Previously de_DE locale will add a *global* 'Tax/Tax Number'
option. This is immediately translated.

This change will upgrade it to be present in all locales, and can be
queried by any report.
---
 libgnucash/app-utils/app-utils.scm      |  3 +++
 libgnucash/app-utils/business-prefs.scm |  6 ++++++
 libgnucash/tax/us/de_DE.scm             |  5 -----
 libgnucash/tax/us/txf-de_DE.scm         | 13 -------------
 4 files changed, 9 insertions(+), 18 deletions(-)

diff --git a/libgnucash/app-utils/app-utils.scm b/libgnucash/app-utils/app-utils.scm
index ca789412ea..fd3f8ef4c2 100644
--- a/libgnucash/app-utils/app-utils.scm
+++ b/libgnucash/app-utils/app-utils.scm
@@ -300,6 +300,8 @@
 (define gnc:*company-contact* (N_ "Company Contact Person"))
 (define gnc:*fancy-date-label* (N_ "Fancy Date Format"))
 (define gnc:*fancy-date-format* (N_ "custom"))
+(define gnc:*tax-label* (N_ "Tax"))
+(define gnc:*tax-nr-label* (N_ "Tax Number"))
 
 (define (gnc:company-info book key)
   ;; Access company info from key-value pairs for current book
@@ -328,6 +330,7 @@
         gnc:*option-name-currency-accounting* gnc:*option-name-book-currency*
         gnc:*option-name-default-gains-policy*
         gnc:*option-name-default-gain-loss-account*
+        gnc:*tax-label* gnc:*tax-nr-label*
         gnc:*option-name-auto-readonly-days* gnc:*option-name-num-field-source*)
 
 (define gnc:*option-section-budgeting* OPTION-SECTION-BUDGETING)
diff --git a/libgnucash/app-utils/business-prefs.scm b/libgnucash/app-utils/business-prefs.scm
index 60f7bf6231..5ec94dbe13 100644
--- a/libgnucash/app-utils/business-prefs.scm
+++ b/libgnucash/app-utils/business-prefs.scm
@@ -157,6 +157,12 @@
     gnc:*option-section-budgeting* gnc:*option-name-default-budget*
     "a" (N_ "Budget to be used when none has been otherwise specified.")))
 
+  ;; Tax Tab
+  (reg-option
+   (gnc:make-string-option
+    gnc:*tax-label* gnc:*tax-nr-label*
+    "a" (N_ "The electronic tax number of your business") ""))
+
   ;; Counters Tab
   (for-each
    (lambda (vals)
diff --git a/libgnucash/tax/us/de_DE.scm b/libgnucash/tax/us/de_DE.scm
index 54bb9f74a6..6388943f2f 100644
--- a/libgnucash/tax/us/de_DE.scm
+++ b/libgnucash/tax/us/de_DE.scm
@@ -49,10 +49,5 @@
 (export txf-asset-categories)
 (export txf-liab-eq-categories)
 
-(define gnc:*tax-label* (N_ "Tax"))
-(define gnc:*tax-nr-label* (N_ "Tax Number"))
-
-(export gnc:*tax-label* gnc:*tax-nr-label*)
-
 (load-from-path "txf-de_DE")
 (load-from-path "txf-help-de_DE")
diff --git a/libgnucash/tax/us/txf-de_DE.scm b/libgnucash/tax/us/txf-de_DE.scm
index c93cdc3f68..92b3d89b75 100644
--- a/libgnucash/tax/us/txf-de_DE.scm
+++ b/libgnucash/tax/us/txf-de_DE.scm
@@ -312,16 +312,3 @@ Fehlermeldungen + Dankschreiben an: stoll@bomhardt.de"))
    )
   )
 ))
-
-;;; Register global options in this book
-(define (book-options-generator options)
-  (define (reg-option new-option)
-    (gnc:register-option options new-option))
-
-  (reg-option
-   (gnc:make-string-option
-    gnc:*tax-label* gnc:*tax-nr-label*
-    "a" (N_ "The electronic tax number of your business") ""))
-  )
-
-(gnc-register-kvp-option-generator QOF-ID-BOOK-SCM book-options-generator)

From 2da5944596f5fdee08293839eada5c2e3e1eda30 Mon Sep 17 00:00:00 2001
From: Christopher Lam <christopher.lck@gmail.com>
Date: Fri, 20 Sep 2019 10:17:08 +0800
Subject: [PATCH 09/14] [taxtxf-de_DE] fix invalid code

(unless book ...) is equivalent to (if (not book) ...) therefore this
snippet was incorrect.

previous commit ensures book always returns a non-#f object therefore
there's no need to handle #f anymore.
---
 gnucash/report/locale-specific/us/taxtxf-de_DE.scm | 7 +------
 1 file changed, 1 insertion(+), 6 deletions(-)

diff --git a/gnucash/report/locale-specific/us/taxtxf-de_DE.scm b/gnucash/report/locale-specific/us/taxtxf-de_DE.scm
index 6557dd0f1c..651785b4fb 100644
--- a/gnucash/report/locale-specific/us/taxtxf-de_DE.scm
+++ b/gnucash/report/locale-specific/us/taxtxf-de_DE.scm
@@ -768,12 +768,7 @@
 	  (to-year    (gnc-print-time64 to-value "%Y"))
           (today-date (gnc-print-time64 (time64CanonicalDayTime (current-time))
                                         "%d.%m.%Y"))
-	  (tax-nr (unless book
-                      (or
-                       (gnc:option-get-value book gnc:*tax-label* gnc:*tax-nr-label*)
-                       "")
-                      ""))
-	  )
+	  (tax-nr (gnc:option-get-value book gnc:*tax-label* gnc:*tax-nr-label*)))
 
       ;; Now, the main body
       ;; Reset all the balance collectors

From 7a662272b31555d010df32f2d4553fec07f3fa5f Mon Sep 17 00:00:00 2001
From: Christopher Lam <christopher.lck@gmail.com>
Date: Fri, 20 Sep 2019 10:39:33 +0800
Subject: [PATCH 10/14] [invoice] render tax/tax number into 'our-details'
 section

---
 gnucash/report/business-reports/invoice.scm | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/gnucash/report/business-reports/invoice.scm b/gnucash/report/business-reports/invoice.scm
index 3bfe1a21b2..af4e29fb47 100644
--- a/gnucash/report/business-reports/invoice.scm
+++ b/gnucash/report/business-reports/invoice.scm
@@ -729,6 +729,7 @@ for styling the invoice. Please see the exported report for the CSS class names.
          (fax (gnc:company-info book gnc:*company-fax*))
          (email (gnc:company-info book gnc:*company-email*))
          (url (gnc:company-info book gnc:*company-url*))
+         (taxnr (gnc:option-get-value book gnc:*tax-label* gnc:*tax-nr-label*))
          (taxid (gnc:company-info book gnc:*company-id*)))
 
     (if (and name (not (string-null? name)))
@@ -766,6 +767,11 @@ for styling the invoice. Please see the exported report for the CSS class names.
                                            (gnc:make-html-div/markup
                                             "maybe-align-right company-tax-id" taxid))))
 
+    (if (and taxnr (not (string-null? taxnr)))
+        (gnc:html-table-append-row!
+         table (list (gnc:make-html-div/markup
+                      "maybe-align-right company-tax-nr" taxnr))))
+
     table))
 
 (define (reg-renderer report-obj)

From 0511ce723ee2ee52a9a5992bced6505577029e17 Mon Sep 17 00:00:00 2001
From: Christopher Lam <christopher.lck@gmail.com>
Date: Fri, 20 Sep 2019 22:17:44 +0800
Subject: [PATCH 11/14] [API] gnc:list-flatten flattens lists recursively

and is a schemey algorithm rather than a report algorithm, so, belongs
centrally.
---
 gnucash/report/standard-reports/budget.scm          | 13 +------------
 .../scm/test/test-libgnucash-scm-utilities.scm      | 12 ++++++++++++
 libgnucash/scm/utilities.scm                        | 12 ++++++++++++
 3 files changed, 25 insertions(+), 12 deletions(-)

diff --git a/gnucash/report/standard-reports/budget.scm b/gnucash/report/standard-reports/budget.scm
index a13b566772..17274811d1 100644
--- a/gnucash/report/standard-reports/budget.scm
+++ b/gnucash/report/standard-reports/budget.scm
@@ -317,17 +317,6 @@
                   (gnc-budget-get-account-period-actual-value budget acct period))
                 periodlist)))
 
-    (define (flatten lst)
-      (reverse!
-       (let loop ((lst lst) (result '()))
-         (if (null? lst)
-             result
-             (let ((elt (car lst))
-                   (rest (cdr lst)))
-               (if (pair? elt)
-                   (loop rest (append (loop elt '()) result))
-                   (loop rest (cons elt result))))))))
-
     ;; Adds a line to the budget report.
     ;;
     ;; Parameters:
@@ -342,7 +331,7 @@
              column-list exchange-fn)
       (let* ((comm (xaccAccountGetCommodity acct))
              (reverse-balance? (gnc-reverse-balance acct))
-             (allperiods (filter number? (flatten column-list)))
+             (allperiods (filter number? (gnc:list-flatten column-list)))
              (total-periods (if accumulate?
                                 (iota (1+ (apply max allperiods)))
                                 allperiods))
diff --git a/libgnucash/scm/test/test-libgnucash-scm-utilities.scm b/libgnucash/scm/test/test-libgnucash-scm-utilities.scm
index a2e0d4d24d..50903c4315 100644
--- a/libgnucash/scm/test/test-libgnucash-scm-utilities.scm
+++ b/libgnucash/scm/test/test-libgnucash-scm-utilities.scm
@@ -10,6 +10,7 @@
   (test-traverse-vec)
   (test-substring-replace)
   (test-sort-and-delete-duplicates)
+  (test-gnc:list-flatten)
   (test-begin "test-libgnucash-scm-utilities.scm"))
 
 (define (test-traverse-vec)
@@ -87,3 +88,14 @@
     '(1 2 3)
     (sort-and-delete-duplicates '(3 1 2) <))
   (test-end "sort-and-delete-duplicates"))
+
+(define (test-gnc:list-flatten)
+  (test-equal "gnc:list-flatten null"
+    '()
+    (gnc:list-flatten '()))
+  (test-equal "gnc:list-flatten noop"
+    '(1 2 3)
+    (gnc:list-flatten '(1 2 3)))
+  (test-equal "gnc:list-flatten deep"
+    '(1 2 3 4 5 6)
+    (gnc:list-flatten '(1 (2) (() () (((((3))) ())) 4 () ((5) (6)))))))
diff --git a/libgnucash/scm/utilities.scm b/libgnucash/scm/utilities.scm
index aa69e277fa..6665f1b97d 100644
--- a/libgnucash/scm/utilities.scm
+++ b/libgnucash/scm/utilities.scm
@@ -47,6 +47,7 @@
 (export gnc:debug)
 (export addto!)
 (export sort-and-delete-duplicates)
+(export gnc:list-flatten)
 
 ;; Do this stuff very early -- but other than that, don't add any
 ;; executable code until the end of the file if you can help it.
@@ -191,6 +192,17 @@
   (define (kons a b) (if (and (pair? b) (= a (car b))) b (cons a b)))
   (reverse (fold kons '() (sort lst <))))
 
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+;; flattens an arbitrary deep nested list into simple list.  this is
+;; probably the most efficient algorithm available. '(1 2 (3 4)) -->
+;; '(1 2 3 4)
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+(define (gnc:list-flatten . lst)
+  (reverse
+   (let lp ((e lst) (accum '()))
+     (if (list? e)
+         (fold lp accum e)
+         (cons e accum)))))
 
 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 ;; compatibility hack for fixing guile-2.0 string handling. this code

From 7587c3b4e337e513a4fb68f4b98bb26740e0f8c2 Mon Sep 17 00:00:00 2001
From: Christopher Lam <christopher.lck@gmail.com>
Date: Fri, 20 Sep 2019 22:42:43 +0800
Subject: [PATCH 12/14] [API] gnc:collector+ and gnc:collector- for collector
 arithmetic

(gnc:collector+ ...) equivalent to (+ ...)
(gnc:collector- ...) equivalent to (- ...) and will also handle
single-argument sign negation.
---
 .../report/report-system/report-system.scm    |  2 ++
 .../report/report-system/report-utilities.scm | 19 +++++++++++++++++++
 .../test/test-report-utilities.scm            | 15 +++++++++++++++
 3 files changed, 36 insertions(+)

diff --git a/gnucash/report/report-system/report-system.scm b/gnucash/report/report-system/report-system.scm
index 33c2229b2b..4c2dd8b925 100644
--- a/gnucash/report/report-system/report-system.scm
+++ b/gnucash/report/report-system/report-system.scm
@@ -693,6 +693,8 @@
 (export gnc:make-value-collector)
 (export gnc:make-number-collector)      ;deprecated
 (export gnc:make-commodity-collector)
+(export gnc:collector+)
+(export gnc:collector-)
 (export gnc:commodity-collector-get-negated)
 (export gnc:commodity-collectorlist-get-merged) ;deprecated
 (export gnc-commodity-collector-commodity-count)
diff --git a/gnucash/report/report-system/report-utilities.scm b/gnucash/report/report-system/report-utilities.scm
index 75cc9979b3..90e5249ba9 100644
--- a/gnucash/report/report-system/report-utilities.scm
+++ b/gnucash/report/report-system/report-utilities.scm
@@ -390,6 +390,25 @@ construct gnc:make-gnc-monetary and use gnc:monetary->string instead.")
 (define (gnc-commodity-collector-allzero? collector)
   (every zero? (map cdr (collector 'format cons #f))))
 
+;; (gnc:collector+ collectors ...) equiv to (+ collectors ...) and
+;; outputs: a collector
+(define (gnc:collector+ . collectors)
+  (let ((res (gnc:make-commodity-collector)))
+    (for-each (lambda (coll) (res 'merge coll #f)) collectors)
+    res))
+
+;; (gnc:collectors- collectors ...) equiv to (- collectors ...), can
+;; also negate single-argument collector. outputs collector
+(define gnc:collector-
+  (case-lambda
+    (() (error "gnc:collector- needs at least 1 collector argument"))
+    ((coll) (gnc:collector- (gnc:make-commodity-collector) coll))
+    ((coll . rest)
+     (let ((res (gnc:make-commodity-collector)))
+       (res 'merge coll #f)
+       (res 'minusmerge (apply gnc:collector+ rest) #f)
+       res))))
+
 ;; add any number of gnc-monetary objects into a commodity-collector
 ;; usage: (gnc:monetaries-add monetary1 monetary2 ...)
 ;; output: a commodity-collector object
diff --git a/gnucash/report/report-system/test/test-report-utilities.scm b/gnucash/report/report-system/test/test-report-utilities.scm
index fd62cc8fc5..79728dade4 100644
--- a/gnucash/report/report-system/test/test-report-utilities.scm
+++ b/gnucash/report/report-system/test/test-report-utilities.scm
@@ -213,6 +213,21 @@
         (gnc:make-gnc-monetary USD 25)
         (coll-A 'getmonetary USD #f))
 
+      (test-equal "gnc:collector+"
+        '(("USD" . 50) ("GBP" . -20))
+        (collector->list
+         (gnc:collector+ coll-A coll-A coll-B)))
+
+      (test-equal "gnc:collector- 1 arg"
+        '(("GBP" . 20) ("USD" . -25))
+        (collector->list
+         (gnc:collector- coll-A)))
+
+      (test-equal "gnc:collector- 3 args"
+        '(("USD" . 25) ("GBP" . -60))
+        (collector->list
+         (gnc:collector- coll-A coll-B coll-B)))
+
       (test-equal "gnc:commodity-collector-get-negated"
         '(("USD" . -25) ("GBP" . 20))
         (collector->list

From f72df3e1bc70b29ca74b12497044f093cc737fbe Mon Sep 17 00:00:00 2001
From: Christopher Lam <christopher.lck@gmail.com>
Date: Sat, 21 Sep 2019 13:49:34 +0800
Subject: [PATCH 13/14] [report-utilities] gnc:account-get-balances-at-dates:
 use quicksort

stable-sort! is slower than quicksort.
---
 gnucash/report/report-system/report-utilities.scm | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/gnucash/report/report-system/report-utilities.scm b/gnucash/report/report-system/report-utilities.scm
index 90e5249ba9..973608af96 100644
--- a/gnucash/report/report-system/report-utilities.scm
+++ b/gnucash/report/report-system/report-utilities.scm
@@ -470,7 +470,7 @@ flawed. see report-utilities.scm. please update reports.")
   (define (amount->monetary bal)
     (gnc:make-gnc-monetary (xaccAccountGetCommodity account) bal))
   (let loop ((splits (xaccAccountGetSplitList account))
-             (dates-list (stable-sort! dates-list <))
+             (dates-list (sort dates-list <))
              (currentbal 0)
              (lastbal 0)
              (balancelist '()))

From 496ca94a989d0001a64c19f5e2104ae02fe1a604 Mon Sep 17 00:00:00 2001
From: Christopher Lam <christopher.lck@gmail.com>
Date: Fri, 20 Sep 2019 22:43:00 +0800
Subject: [PATCH 14/14] [reports] use new API gnc:collector+ and gnc:collector-

---
 .../business-reports/customer-summary.scm     | 17 ++++-----
 .../report/standard-reports/balsheet-pnl.scm  |  5 ++-
 .../standard-reports/category-barchart.scm    | 10 ++----
 .../report/standard-reports/net-charts.scm    |  8 +----
 .../report/standard-reports/trial-balance.scm | 35 +++++++------------
 5 files changed, 24 insertions(+), 51 deletions(-)

diff --git a/gnucash/report/business-reports/customer-summary.scm b/gnucash/report/business-reports/customer-summary.scm
index 2ba1f71b8c..e0ab202cdf 100644
--- a/gnucash/report/business-reports/customer-summary.scm
+++ b/gnucash/report/business-reports/customer-summary.scm
@@ -262,11 +262,6 @@
                  (member (xaccSplitGetAccount s) accounts))
                splits))))
 
-(define (coll-minus minuend subtrahend)
-  (let ((coll (gnc:make-commodity-collector)))
-    (coll 'merge minuend #f)
-    (coll 'minusmerge subtrahend #f)
-    coll))
 
 ;; ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 
@@ -348,7 +343,7 @@
                                (sales (gnc:commodity-collector-get-negated
                                        (filter-splits splits sales-accounts)))
                                (expense (filter-splits splits expense-accounts))
-                               (profit (coll-minus sales expense)))
+                               (profit (gnc:collector- sales expense)))
                           (list owner profit sales expense)))
                       ownerlist))
             (sortingtable '()))
@@ -403,9 +398,10 @@
 
         ;; Add the "No Customer" lines to the sortingtable for sorting
         ;; as well
-        (let* ((other-sales (coll-minus toplevel-total-sales total-sales))
-               (other-expense (coll-minus toplevel-total-expense total-expense))
-               (other-profit (coll-minus other-sales  other-expense)))
+        (let* ((other-sales (gnc:collector- toplevel-total-sales total-sales))
+               (other-expense (gnc:collector- toplevel-total-expense
+                                                  total-expense))
+               (other-profit (gnc:collector- other-sales other-expense)))
           (for-each
            (lambda (comm)
              (let* ((profit (cadr (other-profit 'getpair comm #f)))
@@ -479,7 +475,8 @@
                  (gnc:make-html-text (gnc:html-markup/attr/no-end "hr" "noshade")))))
 
         ;; Summary lines - 1 per currency
-        (let ((total-profit (coll-minus toplevel-total-sales toplevel-total-expense)))
+        (let ((total-profit (gnc:collector- toplevel-total-sales
+                                            toplevel-total-expense)))
           (for-each
            (lambda (comm)
              (let* ((profit (cadr (total-profit 'getpair comm #f)))
diff --git a/gnucash/report/standard-reports/balsheet-pnl.scm b/gnucash/report/standard-reports/balsheet-pnl.scm
index 6f9b3b8d68..bca8f5ad40 100644
--- a/gnucash/report/standard-reports/balsheet-pnl.scm
+++ b/gnucash/report/standard-reports/balsheet-pnl.scm
@@ -961,9 +961,8 @@ also show overall period profit & loss."))
                               asset-liability
                               (lambda (acc)
                                 (gnc:account-get-comm-value-at-date acc date #f))))
-                            (unrealized (gnc:make-commodity-collector)))
-                       (unrealized 'merge asset-liability-basis #f)
-                       (unrealized 'minusmerge asset-liability-balance #f)
+                            (unrealized (gnc:collector- asset-liability-basis
+                                                        asset-liability-balance)))
                        (monetaries->exchanged
                         unrealized common-currency price-source date)))))
              (retained-earnings-fn
diff --git a/gnucash/report/standard-reports/category-barchart.scm b/gnucash/report/standard-reports/category-barchart.scm
index 0da882b7d7..c217a138cd 100644
--- a/gnucash/report/standard-reports/category-barchart.scm
+++ b/gnucash/report/standard-reports/category-barchart.scm
@@ -341,12 +341,6 @@ developing over time"))
                   c report-currency
                   (lambda (a b) (exchange-fn a b date)))))))
 
-          (define (collector-minus a b)
-            (let ((coll (gnc:make-commodity-collector)))
-              (coll 'merge a #f)
-              (coll 'minusmerge b #f)
-              coll))
-
           ;; copy of gnc:not-all-zeros using gnc-monetary
           (define (not-all-zeros data)
             (cond ((gnc:gnc-monetary? data) (not (zero? (gnc:gnc-monetary-amount data))))
@@ -401,8 +395,8 @@ developing over time"))
                           (cdr dates-list)
                           (cons (if do-intervals?
                                     (collector->monetary
-                                     (collector-minus (cadr list-of-mon-collectors)
-                                                      (car list-of-mon-collectors))
+                                     (gnc:collector- (cadr list-of-mon-collectors)
+                                                     (car list-of-mon-collectors))
                                      (cadr dates-list))
                                     (collector->monetary
                                      (car list-of-mon-collectors)
diff --git a/gnucash/report/standard-reports/net-charts.scm b/gnucash/report/standard-reports/net-charts.scm
index d7574a2339..396103b2df 100644
--- a/gnucash/report/standard-reports/net-charts.scm
+++ b/gnucash/report/standard-reports/net-charts.scm
@@ -267,12 +267,6 @@
     ;; conversion function above. Returns a list of gnc-monetary.
     (define (process-datelist account-balances dates left-col?)
 
-      (define (collector-minus coll1 coll2)
-        (let ((res (gnc:make-commodity-collector)))
-          (res 'merge coll1 #f)
-          (res 'minusmerge coll2 #f)
-          res))
-
       (define accountlist
         (if inc-exp?
             (if left-col?
@@ -310,7 +304,7 @@
                   (cons
                    (collector->monetary
                     (if inc-exp?
-                        (collector-minus (car acct-balances) (cadr acct-balances))
+                        (gnc:collector- (car acct-balances) (cadr acct-balances))
                         (car acct-balances))
                     (if inc-exp? (cadr dates) (car dates)))
                    result)))))
diff --git a/gnucash/report/standard-reports/trial-balance.scm b/gnucash/report/standard-reports/trial-balance.scm
index fd726ee71d..e9cfeeac1b 100644
--- a/gnucash/report/standard-reports/trial-balance.scm
+++ b/gnucash/report/standard-reports/trial-balance.scm
@@ -316,19 +316,6 @@
 
     options))
 
-;; (coll-plus collectors ...) equiv to (+ collectors ...)
-(define (coll-plus . collectors)
-  (let ((res (gnc:make-commodity-collector)))
-    (for-each (lambda (coll) (res 'merge coll #f)) collectors)
-    res))
-
-;; (coll-minus collectors ...) equiv to (- collector0 collector1 ...)
-(define (coll-minus . collectors)
-  (let ((res (gnc:make-commodity-collector)))
-    (res 'merge (car collectors) #f)
-    (for-each (lambda (coll) (res 'minusmerge coll #f)) (cdr collectors))
-    res))
-
   ;;;;;;;;;;;;;;;;;;;;;;;;;;;
 ;; trial-balance-renderer
 ;; set up the document and add the table
@@ -531,7 +518,7 @@
                 (let* ((cost-fn (gnc:case-exchange-fn
                                  'average-cost report-commodity end-date))
                        (acct-balances (map acct->bal all-accounts))
-                       (book-balance (apply coll-plus acct-balances))
+                       (book-balance (apply gnc:collector+ acct-balances))
                        (value (gnc:sum-collector-commodity
                                book-balance report-commodity exchange-fn))
                        (cost (gnc:sum-collector-commodity
@@ -674,17 +661,19 @@
                      (pos-adjusting
                       (and ga-or-is? (sum-account-splits acct adjusting-splits #t)))
                      (neg-adjusting
-                      (and ga-or-is? (coll-minus adjusting pos-adjusting)))
-                     (pre-closing-bal (coll-minus curr-bal closing))
-                     (pre-adjusting-bal (coll-minus pre-closing-bal adjusting))
+                      (and ga-or-is? (gnc:collector- adjusting pos-adjusting)))
+                     (pre-closing-bal (gnc:collector- curr-bal closing))
+                     (pre-adjusting-bal (gnc:collector- pre-closing-bal
+                                                        adjusting))
                      (atb (cond ((not is?) pre-closing-bal)
                                 ((double-col 'credit-q pre-adjusting-bal
                                              report-commodity exchange-fn show-fcur?)
-                                 (list (coll-plus pos-adjusting)
-                                       (coll-plus neg-adjusting pre-adjusting-bal)))
+                                 (list (gnc:collector+ pos-adjusting)
+                                       (gnc:collector+ neg-adjusting
+                                                       pre-adjusting-bal)))
                                 (else
-                                 (list (coll-plus pos-adjusting pre-adjusting-bal)
-                                       (coll-plus neg-adjusting))))))
+                                 (list (gnc:collector+ pos-adjusting pre-adjusting-bal)
+                                       (gnc:collector+ neg-adjusting))))))
 
                 ;; curr-bal = account-bal with closing & adj entries
                 ;; pre-closing-bal = account-bal with adj entries only
@@ -851,8 +840,8 @@
                  (tot-abs-amt-cell bs-credits))
                 '())))
           (if (eq? report-variant 'work-sheet)
-              (let* ((net-is (coll-minus is-debits is-credits))
-                     (net-bs (coll-minus bs-debits bs-credits))
+              (let* ((net-is (gnc:collector- is-debits is-credits))
+                     (net-bs (gnc:collector- bs-debits bs-credits))
                      (tot-is (gnc:make-commodity-collector))
                      (tot-bs (gnc:make-commodity-collector))
                      (is-entry #f)