Detecting Changes in Value
If the event expression ch(), tr() or fs() is applied to an expression that uses a Data-Item or condition, it is necessary to preserve the previous value of the element. This is done by maintaining a duplicate copy of the element that is updated at the end of every step. (This makes detecting ch() on a large array or complex record a very slow process, because it takes time on every step.) The duplicate copy of the variable is named prev_<element>.
The following table lists the affected element types:
define base Data-Item holds value of Data-Item holds wr() event for Data-Item holds rd() event for Data-Item holds old value of the Data-Item
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Element—is the name of the element as listed in the .info file. This is normally the same as the Element Name in the Properties, unless there are duplicate Element Names.
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Type—is the name of the User-Defined Type. It is also listed in the info file.