You specify the response to interval statement when you want one or more actions to occur every n seconds during the execution of an ESL program, or of any block within it.

 

In the following example, information in Status_Region is flashed on the screen every 60 seconds, and the time is updated.

 

response to interval 60

    read file Status into Status_Region

    change Clock to time

 

If other actions are taking place while the specified seconds have elapsed, response to interval takes place after the previous actions are completed. If the previous actions exceed the specified interval two or more times, response to interval  responds to the last interval only.

 

A response to interval statement can be specified within a block. The following example shows two response to interval statements, one inside Block_1 and one in the main program. When the program is in Block_1, only the response to interval 15 is valid.

 

response to interval 60

    ...

 

response to Main_Menu

    begin guarded Block_1

        response to Restart

            enable Open_Menu

            leave block

        response to interval 15

            add to Timer

                pattern Graphics

    end Block_1

 

If Block_1 was not guarded and Main_Menu was selected, the response to interval 15 would occur until 60 seconds passed; then the response to interval 60 would occur, causing Block_1 to be exited.