[Twine 2][Harlowe 3] can we use operator like "+" or "-" with datamaps macro

hello everyone, i’m still stuck in making inventory right now and i have a question. so, i’ve been thinking of using datamap (dm:) macro to replace the array (a:) macro to make it more organized (to make the inventory into a list). the problem is, when i tried to like reduce the number of the value it contains, it doesn’t work.

this is the story macro for the inventory i currently make.

set: $sword1 to 1)(set: $bow to 8) (set: $inventory to (a:(dm: $sword1, “swords”,
8, “bows”)))

you have:
$inventory

(if: $sword1 > 0)[you equipped the sword (set: $sword1 to $inventory’s swords - 1)]

you have:
$inventory

can someone help me?