Add two (for the moment undocumented) functions:

- commodity_price(NAME, DATE)
- set_commodity_price(NAME, DATE)

Using these two I am able to compute rate of return over a period of
transactions, taking additional deposits and withdrawals into account, using
the following automated transactions:

  P 2019-12-31 12:00:00 ROI $1.00

  2020-01-01 Start of record
      (ROI)  0 ROI

  = expr date >= [2020/01/01] && account =~ /Broker:Cash$/ and any(account =~ /Assets:Checking/)
      (ROI)  (1 ROI * (amount / commodity_price(1 ROI, date)))

  = expr date >= [2020/01/01] && account =~ /:Capital:/
      (ROI)  (set_commodity_price(1 ROI, date, ((commodity_price(1 ROI, date) * account("ROI").amount) - amount) / account("ROI").amount) || 0 ROI)

1 files changed, 2 insertions, 0 deletions

diff --git a/src/report.h b/src/report.h
index 5325c3a2..c1dc75c2 100644
--- a/src/report.h
+++ b/src/report.h
@@ -189,6 +189,8 @@ public:
   value_t fn_ansify_if(call_scope_t& scope);
   value_t fn_percent(call_scope_t& scope);
   value_t fn_commodity(call_scope_t& scope);
+  value_t fn_commodity_price(call_scope_t& scope);
+  value_t fn_set_commodity_price(call_scope_t& scope);
   value_t fn_nail_down(call_scope_t& scope);
   value_t fn_lot_date(call_scope_t& scope);
   value_t fn_lot_price(call_scope_t& scope);