Conditional Processing

DPML provides two conditional statements an if-then-else and a choose statement.

if-then-else

The structure of the if statement is:

When program flow enters the <if> block the instructions within the <cond> block are executed first. A resource identified by the URI this:cond is associated with the <cond> block. The instructions within a <cond> block must, at some point before the end of the block, assign a boolean to this:cond. The IAspectBoolean associated this:cond is evaluated as the result of the <cond> block and the conditional branch is performed. If the resource identified by this:cond represents true the <then> block is executed otherwise the <else> block is executed.

The following example program illustrates how to set the resource this:cond to true. Copy and paste this program into the DPML Playpen to see the results and experiment with the conditional structure.

This example uses a canonical document for the boolean value. NetKernel will automatically transrept the canonical XML boolean document into an IAspectBoolean representation with the appropriate value when it is set to the resource this:cond.

choose

The structure of the choose statement is:

When program flow enters the <choose> block the <cond> blocks are executed in document order until one evaluates to true. When a true condition is found the following <then> block is executed and all subsequent blocks are ignored. If none of the <cond> blocks evaluates to true then an existing <else> block is executed.