Section 4 Types: TBD: Should "blank" also be a possible value result?

[Eike Rathke <erack@sun.com>]

Hi,

Section "4 Types" has

| TBD: Should "blank" also be a possible value result? This is needed for
| empty parameters; it can also occur with an intersection of
| non-overlapping references. For the moment, presume that it's a kind
| of reference (a reference with no cells as content). But are they
| distinguishable?  And what is the type of an empty cell?  Empty is
| distinguishable from a zero-length Text value, because COUNTA makes this
| distinction.

Actually we need both and have to distinguish between an "empty cell"
and a "no cell" as in the intersection case. A "no cell" intersection is
a reference error. An "empty cell" return value for example is needed
in [HV]LOOKUP results, where for an empty cell the expression
ISBLANK(LOOKUP(...)) must yield TRUE (OOo doesn't implement that yet).
An "empty cell" value is undetermined until evaluated, which is needed
in comparisons where with an empty cell A1 (or a LOOKUP result) both
expressions IF(A1=0) and IF(A1="") yield TRUE.

An empty cell passed as parameter will never be the same as an omitted
parameter, at least to my knowledge. Any other observations?

  Eike

-- 
Automatic string conversions considered dangerous. They are the GOTO statements
of spreadsheets.  --Robert Weir on the OpenDocument formula subcommittee's list.