[VFP] Unimplemented _Tally system variable

[cpyrgas]

Found this code, which is currently causing a parser error XS9002: Parser: unexpected input ':='

COUNT FOR stocklist.Selected = .T.
nCount = _tally

There are two issues here:

• COUNT FOR command is not accepted without a TO clause
• _TALLY is defined in the runtime, but is not used at all. According to https://hackfox.github.io/section4/s4g097.html, it is affected by many commands and functions:

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Here is the complete list of commands that change _TALLY (well, we think it’s complete—we tried a bunch of undocumented stuff):

Append From
Average
Blank
Calculate
Copy To
Copy To Array
Count

Delete
Delete-SQL
Export
Index
Pack
Recall
Reindex

Replace
Replace From Array
Select-SQL
Sort
Sum
Update-SQL

Actually, JOIN, TOTAL and UPDATE are documented as changing _TALLY, too, but they’re so obsolete, we didn’t even test them. A good thumbrule is that _TALLY is updated by every command that displays a record count when TALK is ON.

Generally, _TALLY contains the number of records affected by the command. So, after DELETE, it has the number of records deleted; after REPLACE, _TALLY contains the number of records that had a field replaced.

However, there's one real oddity on this list. _TALLY after REINDEX contains the number of records for which the last tag indexed applies. If you have filtered tags (indexes using a FOR clause), _TALLY returns the number of records contained in the last index. "Last" here refers to the creation order of the tags, since they're re-created in the same order. This isn't really a big problem since we suggest you never use REINDEX anyway.

In VFP 3 and VFP 5, when TALK is OFF, INDEX and REINDEX don't update _TALLY. This bug is fixed in VFP 6.