4.1.8 Other Operations on Lists

As was mentioned earlier, lists can be constructed by writing a comma-separated sequence of expressions inside curly braces:

{expression-1, expression-2, ..., expression-N}

The resulting list has the value of expression-1 as its first element, that of expression-2 as the second, etc.

{3 < 4, 3 <= 4, 3 >= 4, 3 > 4} => {1, 1, 0, 0}

Additionally, one may precede any of these expressions by the splicing operator, `@'. Such an expression must return a list; rather than the old list itself becoming an element of the new list, all of the elements of the old list are included in the new list. This concept is easy to understand, but hard to explain in words, so here are some examples. For these examples, assume that the variable a has the value {2, 3, 4} and that b has the value {"Foo", "Bar"}:

{1, a, 5} => {1, {2, 3, 4}, 5} {1, @a, 5} => {1, 2, 3, 4, 5} {a, @a} => {{2, 3, 4}, 2, 3, 4} {@a, @b} => {2, 3, 4, "Foo", "Bar"}

If the splicing operator (`@') precedes an expression whose value is not a list, then E_TYPE is raised as the value of the list construction as a whole.

The list membership expression tests whether or not a given MOO value is an element of a given list and, if so, with what index:

expression-1 in expression-2

Expression-2 must return a list; otherwise, E_TYPE is raised. If the value of expression-1 is in that list, then the index of its first occurrence in the list is returned; otherwise, the `in' expression returns 0.

2 in {5, 8, 2, 3} => 3 7 in {5, 8, 2, 3} => 0 "bar" in {"Foo", "Bar", "Baz"} => 2

Note that the list membership operator is case-insensitive in comparing strings, just like the comparison operators. To perform a case-sensitive list membership test, use the `is_member' function described later. Note also that since it returns zero only if the given value is not in the given list, the `in' expression can be used either as a membership test or as an element locator.