Although compiling details are transparent to users some information may be useful.
The source program is written in a file. It is read and processed by the GLIDER compiler that translates it to several units of Pascal code.
The program code of the nodes are translated into procedures. The messages are translated into records that may have different structures, according to the fields declared in the MESSAGES declarations. The actual items that are in the ELs and ILs are fixed structure records (for all kinds of messages) called indicators of messages. They have pointers to the true messages, and some auxiliary fields: number of the message, original node name and pointer to the following indicator in the list (or NIL if it is the last).
The program so produced by the GLIDER compiler may be then compiled and executed by a Pascal system.