Extended syntax for the expressions (statements) of eval tags and calculated historical values

The following chapter describes the syntax that is usable in the expressions of objects of Eval tag type and the statements of objects of Historical value type.

Initialization part

The initialization part must always start with the INIT keyword. This part may contain:

• declarations of local variables,
• labels,
• GOTO label: commands,
• IF condition GOTO label: commands
  
  • label must be always finished by the character ":" (as well as label in GOTO commands),
• commands based on conditional evaluation,
      IF condition1 THEN
          action1
      ELSIF condition2 THEN
          action2
      ELSIF condition3 THEN
          action3
          .....
      ELSE
          action
      ENDIF
• command RETURN ends the calculation and assigns the value to result (constant or expression) after RETURN command,
• command EXIT causes a move on part FINALLY.

The initialization part is optional. If it is not declared, the original syntax is valid.
If the initialization part has been declared, the expressions, determining the value of the object, must be specified after the FINALLY keyword.

Limitations

The number of executed rows is limited in D2000 systems. Nowadays, the number cannot be defined or changed at all.
The number (ExecuteRows) depends on the type of used process.

For process D2000 Calc:

• ExecuteRows > 1000 - the following log: "EvalTag_Name - executed rows : row_count" is to be written into the log file of process D2000 Calc (calc.log)
• ExecuteRows > 100 000 - the system variable SystemError acquires the following value: "EvalTag_Name - infinite loop"

For process D2000 Archiv:

• ExecuteRows > 1000 - the following log: "HistoricalValue_Name - executed rows : row_count" is to be written into the log file of process D2000 Archiv (archiv.log)
• ExecuteRows > 10 000 - the system variable SystemError acquires the following value: "HistoricalValue_Name - infinite loop"

If the value of different type is assigned to the system variable, a runtime error occurs while the expression is executing. The runtime error stops the script evaluation (the other rows will not be evaluate) and always returns Invalid value. To display this error, activate "debug runtime errors".

An exceptions:

• a mutual conversion HBJ - Integer
• a mutual conversion Relative time - Real - Integer
• a direct conversion from Boolean to Relative time, Real or Integer

Example 1

Calculation of the sum of the values in the column A2 of the structured variable SV. The sum only includes the values of the lines, where the value in the column A1 is greater or equal to 3.

INIT

INT _rows
INT _rowNr
REAL _sum

_rows := SV.A\DIM
_sum := 0.0

START:
_rowNr :=1

CYCLE:
IF SV.A[_rowNr]^A1 < 3 GOTO SKIP:
_sum := _sum + SV.A[_rowNr]^A2

SKIP:
_rowNr := _rowNr + 1

IF _rowNr <= _rows GOTO CYCLE:


FINALLY

_sum

Example 2

This example shows a sequence of one third of running minute - three ways of value return.

INIT

INT _third

IF Sec <= 20 THEN   
    RETURN 1
ELSIF Sec <= 40 THEN
   _third := 2
    RETURN _third
ELSE
   _third := 3
    EXIT
ENDIF

FINALLY
_third

In both examples, the time stamp of expression will acquire the time of evaluation of the expression. If the expression is expected to acquire other value than the time of evaluation of the expression, it should be defined in the expression (after FINALLY!).

Example:

FINALLY
%NtV(_sum, _time)

To define the user flags for the resultant value of expression, specify the definition of user flag in the expression.

Example:

FINALLY
%SetFlags(_sum, @A, _boolean)