Nested blocks are important for controlling program flow. They also come into play when a block is exited without an explicit leave block statement (described in Leaving (Exiting) a Block). When using nested blocks, name each one for clarity.

 

Blocks can be nested within other blocks, creating a program that contains many levels of responses, ranging from the innermost to the outermost. One way of understanding nested blocks is to consider the entire ESL program itself as a block. The following is an example of a nested block:

 

# Action routine:

 

action DialBlock is

    send "AT\r\n" to DJNS

    begin CheckOK1

        response to line "OK" from DJNS

            leave block

        response to line "ERROR" from DJNS

            action ErrorWait

    end CheckOK1

 

    change Prompt to

        move to (xsize/2) (ysize/2)

        font "large" text center "Dialing ..."

    send "ATDT" Phonenum "\r\n" to DJNS

    begin CheckConnect                    # Outer block

        response to line "Connect" from DJNS

            action Logon

            leave block

        response to line "Error" from DJNS

            action ErrorWait

        response to Quit

            send "\r\n" to DJNS

            begin CheckOK2                # Inner block

                response to line "OK" from DJNS

                    leave block

                response to line "ERROR" from DJNS

                    action ErrorWait

            end CheckOK2

            leave block

    end CheckConnect

 

When blocks are nested, control can be transferred from one block to any of the blocks that are outside that block (at a higher level of nesting). There might be more than one block at any given level, but only one of these can be active at any given time. These situations are discussed in the following section.