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ListValid

Determines if an expression is a list.

Synopsis

ListValid(exp)

Parameters

exp Any valid expression. A valid list must be created using ListBuild or ListFromString, or extracted from another list using List. The null string ("") is also treated as a valid list.

Description

ListValid determines whether exp is a list, and returns a Boolean value: If exp is a list, ListValid returns 1; if exp is not a list, ListValid returns 0.

A list can be created using ListBuild or ListFromString, or extracted from another list using List. A list containing the empty string ("") as its sole element is a valid list. The empty string ("") by itself is also considered a valid list.

Examples

The following examples all return 1, indicating a valid list:

 w = ListBuild("Red","Blue","Green")
 x = ListBuild("Red")
 y = ListBuild(365)
 z = ListBuild("")
 Println ListValid(w)
 Println ListValid(x)
 Println ListValid(y)
 Println ListValid(z)
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The following examples all return 0. Numbers and strings (with the exception of the null string) are not valid lists:

 x = "Red"
 y = 44
 Println ListValid(x)
 Println ListValid(y)
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The following examples all return 1. Concatenated, nested, and omitted value lists are all valid lists:

 w = ListBuild("Apple","Pear")
 x = ListBuild("Walnut","Pecan")
 y = ListBuild("Apple","Pear",ListBuild("Walnut","Pecan"))
 z = ListBuild("Apple","Pear",,"Pecan")
 Println ListValid(w & x)    ' concatenated
 Println ListValid(y)      ' nested
 Println ListValid(z)      ' omitted element
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The following examples all return 1. ListValid considers all of the following “empty” lists as valid lists:

Println ListValid("")
Println ListValid(ListBuild())
Println ListValid(ListBuild(NULL))
Println ListValid(ListBuild(""))
Println ListValid(ListBuild(Chr(0)))
Println ListValid(ListBuild(,))
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See Also