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13.33. Accumulate with Inline Custom Code

Warning

The use of accumulate with inline custom code is not a good practice for several reasons, including difficulties on maintaining and testing rules that use them, as well as the inability of reusing that code. Implementing your own accumulate functions allows for simpler testing. This form of accumulate is supported for backward compatibility only.
The general syntax of the accumulate CE with inline custom code is: 
<result pattern> from accumulate( <source pattern>,
                                  init( <init code> ),
                                  action( <action code> ),
                                  reverse( <reverse code> ),
                                  result( <result expression> ) )
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The meaning of each of the elements is the following:
  • <source pattern>: the source pattern is a regular pattern that the engine will try to match against each of the source objects.
  • <init code>: this is a semantic block of code in the selected dialect that will be executed once for each tuple, before iterating over the source objects.
  • <action code>: this is a semantic block of code in the selected dialect that will be executed for each of the source objects.
  • <reverse code>: this is an optional semantic block of code in the selected dialect that if present will be executed for each source object that no longer matches the source pattern. The objective of this code block is to undo any calculation done in the <action code> block, so that the engine can do decremental calculation when a source object is modified or retracted, hugely improving performance of these operations.
  • <result expression>: this is a semantic expression in the selected dialect that is executed after all source objects are iterated.
  • <result pattern>: this is a regular pattern that the engine tries to match against the object returned from the <result expression>. If it matches, the accumulate conditional element evaluates to true and the engine proceeds with the evaluation of the next CE in the rule. If it does not matches, the accumulate CE evaluates to false and the engine stops evaluating CEs for that rule.
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