Concept of "Excel [Blank] Cell" in any programming language?-CodePudding

Excel has a Blank cell which has some interesting properties when it comes to calculations:

In the below we will assume cell A1 is blank.

A blank cell equals another blank cell: =A1=A1.
A blank cell equals '', 0, and FALSE: =A1="", =A1=0, =A1=FALSE.
A blank cell will coerce to the expected operand type: =A1 A1 (0), =-A1 (0), =A1&A1 ("").

I suppose the closest item I've found is the bool function in python, which covers the first two cases above:

bool(None) == bool(None)
bool(None) == bool(0), bool(None) == bool(''), bool(None) == bool(False)

But that doesn't cover the third case where it implicitly casts to the expected type. Is there anything in a language that covers that?

Here is a video showing some of the properties: https://gyazo.com/b23989ba1fd28500aff32a6b6cb6dca5.

CodePudding user response：

A blank cell in Excel is not a data type but it is an object with multiple parameters.
Blank cell equals depend on the blank cell and the other value or cell type.
Remember that an empty cell in Excel could be a date or currency or Boolean

So the closest thing to Excel's blank cell is really 'null' in most programming languages. a blank cell is state rather than data type.

CodePudding user response：

Is there anything in a language that covers that?

Short answer:

Languages that support syntactic unification, e.g. Prolog, Datalog, Answer Set Programming, ... .
These programming languages are typically Logic programming languages.

Here are demonstrations of your list using SWI-Prolog

Note: In Prolog = is unification not comparison ==. In some situations if you think of a variable as a named pointer and unification as setting pointers equal it makes sense but that analogy works only in specific cases, you have been warned.

A blank cell equals another blank cell: =A1=A1.

?- A = B.
A = B.

Now if A is bound to a value then B is also bound because they are unified.

?- A = B,A=1.
A = B, B = 1.

A blank cell equals '', 0, and FALSE: =A1="", =A1=0, =A1=FALSE.

I will take that to mean that a blank cell has a primitive data type with a default value of that type.

Since Prolog is not strongly typed a variable has no type until a value is bound to the variable, think Python with Duck typing. Even then the concept of a specific type may not be what one expects.

However when the second statement is considered with the third statement

A blank cell will coerce to the expected operand type: =A1 A1 (0), =-A1 (0), =A1&A1 ("").

then as noted the Prolog variable (Excel blank cell) acquires the type upon binding.

?- (var(B)->write('B is variable');write('B is not variable')),nl,(integer(B)->write('B is integer');write('B is not integer')),nl,A is 2,(integer(A)->write('A is integer');write('A is not integer')),nl,A=B,(integer(B)->write('B is integer');write('B is not integer')).
B is variable
B is not integer
A is integer
B is integer
B = A, A = 2.