Zilde

is the empty numeric vector. It is the shape of any scalar, although its own shape is. This is because it has rank 1 (i.e. it is a vector), so it has exactly one axis (i.e. its shape is a 1-element vector) with the length 0. (Zilde's shape cannot be Zilde, as that would indicate that it had rank 0, i.e. it were a scalar.) Zilde is equivalent to  and   and. Being numeric, Zilde's prototype is 0.

Zilde is notable for being an APL glyph which represents an array rather than a primitive function or primitive operator. In most APLs it is the only array literal which is produced using its own token rather than being part of a family of array literals like numeric literals, strings, or system constants. Exceptions are:


 * Dyalog APL's  which is the current workspace's root namespace
 * SHARP APL's  which is nil, or
 * NARS2000 and ngn/apl's  denoting infinity

It should be noted that the empty numeric vector is distinct from the empty character vector  while comparing "all" their elements would seem to indicate that they are identical: This is because  itself returns an empty numeric vector, and reducing an empty vector with the Logical And function  yields the identity element of Logical And, which is 1.