Halliday's three macrofunctions of language

When I was teaching 2° grade some years ago, we did the following activity, which can be analized according to the macrofunctions of language described by Hallyday.
After studying the toys and numbers up to 20, I asked the students to bring their toys to class. We designed a toy shop in the classroom and put prices to the toys. Some students were the sales assistants and others the customers.
Students loved the activity and it showed how much they had learnt!

TASK	MACROFUNCTION	MICROFUNCTION	GRAMMAR
Role Play. You are in a toy shop and you have $20. Your partner is the sales assistant. Look at the toys and prices, what do you want to buy?	Exchanging goods and services.	Asking about and stating prices.	How much is it?/ Here you are/ Thanks/ Vocabulary: toys and numbers.