ProLinga

The 4GL engine processes statements that have been generated from 4GL logic by the generator. 4GL statements typed in by a developer user may look like this for instance:

SCREEN TITLE "Variable - untitled"
MESSAGE "Created new variable."
CLEAR RECORD Variable.Variable
LET F-EditCode.Variable P-EditCode(1)
DISPLAY ALL

To be able to process these statements we need to put them in a format that can be processed in an efficient way by the interpreter. When this logic is saved in the 4GL development tool, an XML document will be generated by the Validate Web Service that looks like this:

<?xml version="1.0"?>
<ProLinga>
  <Runner version="1.0">
    <Statements>
      <Statement SequenceNo="1" NextTrue="2" NextFalse="2" Command="2">
        <Arguments>
          <Argument>TITLE</Argument>
          <Argument>"Variable -  untitled"</Argument>
        </Arguments>
      </Statement>
      <Statement SequenceNo="2" NextTrue="3" NextFalse="3" Command="3">
        <Arguments>
          <Argument>"Created new variable."</Argument>
        </Arguments>
      </Statement>
      <Statement SequenceNo="3" NextTrue="4" NextFalse="4" Command="4">
        <Arguments>
          <Argument>RECORD</Argument>
          <Argument>Variable.Variable</Argument>
        </Arguments>
      </Statement>
      <Statement SequenceNo="4" NextTrue="5" NextFalse="5" Command="5">
        <Arguments>
          <Argument>F-EditCode.Variable</Argument>
          <Argument>P-EditCode(1)</Argument>
        </Arguments>
      </Statement>
      <Statement SequenceNo="5" NextTrue="0" NextFalse="0" Command="8">
        <Arguments>
          <Argument>ALL</Argument>
        </Arguments>
      </Statement>
    </Statements>
  </Runner>
</ProLinga>

Besides the statements and arguments, this document also contains control information as where to go after processing a statement. This is important when using statements like IF/THEN/ELSE or FOREVER loops. All data references also have been validated for their existence. While for the developer user it seems that the interpreter is a 4GL interpreter, in fact it is an XML interpreter. Using this format also opens the door for features as code generation and scripting. Since the XML parser used from libxml2 is as so called DOM parser, this model will work best with logic blocks of limited size. Benchmark test should tell us, but initial testing suggests a maximum of 500 lines per logic block must be set. For a 4GL this is a very reasonable limitation.