Architecture/Design patterns of Structured Text program

Many sources for good software architecture will use objects, pointers, memory allocation in their solutions. The PLC programming language 61131-3 Structured Text is really limited in this regard, more like a limited version of Pascal. Reasons for this are often cited as i.e. safety and determinism.

Here are some of the limitations

• No pointers
• No objects
• No memory allocation
• No first class functions

(Please note that I am using Siemens SCL, that is, no support for Codesys/Beckhoff extensions with objects, references an so on.)

How do I build a good architecture with these limitations, even ANSI C architecture/design pattern sources use a little bit of dynamism like callbacks or lists of function pointers etc.

I try to use the good SOLID principles, and other "best practices" but for me thats more programming in the small, not the big picture.

What are some good sources too look at/tips for building a good architecture with these limitations in the language?

Thanks