Syntax Extensions

Nested Lists

Normally a list in Arden Syntax is flat, i.e., it may not contain lists. However, in some special cases, nested lists are allowed, or even required.

Type	Description
Argument assignment	The argument element may contain nested lists, e.g., a collection of ss records and fields from a database. Example: input := ARGUMENT;
Read statement	The result of a read statement may also be a nested list. Example: res := READ { read_key_res };
Call statement	Each operand of called modules (MLMs, events, or interfaces) can be lists, and thus packed together as a nested list. The result may be a nested list as well Example: res := CALL module1 WITH arg1, arg2;
Return statement	Analogous to call statements, the arguments of a return statement may also be lists, and therefore combined to a nested list. Example: RETURN res1, (res2_1, res2_2), res3;

Within this documentation, "nested lists" are referred to as "compound lists" and are only allowed in the aforementioned four scenarios, but have implications for the syntax. In all other list use cases, lists are assumed to be flat, and the use of compound lists is not allowed.

Incoming Values

General Compound List Handling

Inside a read statement, the <mapping> may return a compound list. Therefore, all operators which are possible in the <constraint> or <aggregation> part of the statement must be able to handle such compound lists.
According to the Arden Syntax definition (Section 9.7) for the <constraint> part, these are:

• Occur [not] Equal
• Occur [not] Within ... To
• Occur [not] Within ... Preceding
• Occur [not] Within ... Following
• Occur [not] Within ... Surrounding
• Occur [not] Within Past
• Occur [not] Within Same Day As
• Occur [not] Before
• Occur [not] After
• Occur [not] At

The <aggregation> part may contain the following operators, so they also have to handle compound lists:

• exist
• sum
• average
• avg
• minimum
• min
• maximum
• max
• last
• first
• earliest
• latest
• minimum ... from
• min ... from
• max ... from
• maximum ... from
• last ... from
• first ... from
• earliest ... from
• latest ... from

All aforementioned operators accept compound lists as parameters. Example:

FIRST 2 FROM ((1,2,3),(4,5,6),(7,8,9)); results in ((1,2),(4,5),(7,8))

Assignment

For incoming values via the special variable ARGUMENT, a READ statement, or a CALL statement, the situation is more complex. Its value may contain a single value, a flat list, or a compound list. The Arden Syntax definition does not describe how the assignment of such values has to be done. The following cases have to be distinguished (parentheses denote flat lists, parentheses with an exclamation point denote compound lists):

Variable	Expression	Result
inp	1	inp := 1;
inp	()	inp := ();
inp	(1)	inp := (1);
inp	(1, 2)	inp := (1, 2);
inp	(!)	inp := null;
inp	(!1)	inp := 1;
inp	(! (1, 2) )	inp := (1, 2);
inp	(!1, 2)	inp := (!1, 2);
(inp1, inp2)	1	inp1 := 1; inp2 := null;
(inp1, inp2)	()	inp1 := null; inp2 := null;
(inp1, inp2)	(1)	inp1 := 1; inp2 := null;
(inp1, inp2)	(1, 2)	inp1 := 1; inp2 := 2;
(inp1, inp2)	(!)	inp1 := null; inp2 := null;
(inp1, inp2)	(!1)	inp1 := 1; inp2 := null;
(inp1, inp2)	(! (1, 2))	inp1 := (1, 2); inp2 := null;
(inp1, inp2)	(!1, 2)	inp1 := 1; inp2 := 2;