Generate clauses of which

[vale1410]

The following program should not generate any unit clauses:

#ground f[1],f[2],f[3]. 
f[X] :: var(X). 

Bule grounds this to:

Warning. Undeclared variables: var(1) var(2) var(3)

 var(1).
 var(2).
 var(3).

It's good that it notifies that clauses are generated of which no variables are introduced.
In my opinion it should not generate the clauses at all.

For example:

#ground f[1],f[2].     
f[X] :: #exists[0] foo(X).  
f[X] :: bar(X) | foo(X). 

In my opinion it should not generate the clauses.

Alternative option: it generates the clauses with the atoms that have been introduced.

[AbdallahS]

I like the current approach with a warning and printing the clauses anyway because seeing what is being generated can help one see in which clause type the undeclared variable is being used. If it just printed "undeclared variable xyz" then the user would need to mentally perform the grounding to identify the offending rule.

Furthermore, some debugging techniques, like adding a debug literal, would be made heavier if the user also had to declare the debug variable each time.