Answer:
The poem is loosely structured overall but does have some elements that make structure.
Step-by-step explanation:
The poem does not rhyme and is very freely written. but it does start with "The" in most lines as it tells us who is singing:
"The carpenter singing his as he measures his plank or beam,
The mason singing his as he makes ready for work, or leaves off work,
The boatman singing as he sits on his bench, the hatter singing as he stands"
So, considering the verses above, it would be correct to say that it has some sort of structure.