remove-atom doesn't work when an atom contains a python object

[bowen-xu]

Describe the bug
When an atom contains a python project, like (Item 1 2 <py-boject>), operationremove-atom doesn't work in some case.

See the code below.

!(bind! &my-space (new-space))

(= (add-item $x1 $x2)
    (add-atom &my-space (Item $x1 $x2 (py-tuple ($x1 $x2))))
)
(= (get-item $x1 $x2)
    (match &my-space (Item $x1 $x2 $x3) (Item $x1 $x2 $x3))
)
!(add-item 1 2)
!(get-item 1 2)
!(let $item (get-item 1 2)
    (remove-atom &my-space $item)
)
!(get-item 1 2)
!(remove-atom &my-space (Item 1 2 (py-tuple (1 2))))
!(get-item 1 2)

the output is

[()]
[()]
[(Item 1 2 (1, 2))]
[()]
[(Item 1 2 (1, 2))]
[()]
[]

This sentence !(let $item (get-item 1 2) (remove-atom &my-space $item)) does not really remove the item from the space.
Because !(get-item 1 2) after that produce [(Item 1 2 (1, 2))].

However, !(remove-atom &my-space (Item 1 2 (py-tuple (1 2)))) works well.

To compare, consider the following code

!(bind! &my-space (new-space))

(= (add-item $x1 $x2)
    (add-atom &my-space (Item $x1 $x2))
)
(= (get-item $x1 $x2)
    (match &my-space (Item $x1 $x2) (Item $x1 $x2))
)
!(add-item 1 2)
!(get-item 1 2)
!(let $item (get-item 1 2)
    (remove-atom &my-space $item)
)
!(get-item 1 2)

the output is

[()]
[()]
[(Item 1 2)]
[()]
[]

which shows that !(let $item (get-item 1 2) (remove-atom &my-space $item)) succesfully removes the item.
The only differnece is whether the atom contains a python object ((Item 1 2 (py-tuple (1 2))) vs (Item 1 2)).

In my application, I have to contain a python object in an atom. Is that a bug or not?

To Reproduce
Run the code snippets through https://metta-lang.dev/docs/playground/playground.html

Expected behavior
Given

!(bind! &my-space (new-space))

(= (add-item $x1 $x2)
    (add-atom &my-space (Item $x1 $x2 (py-tuple ($x1 $x2))))
)
(= (get-item $x1 $x2)
    (match &my-space (Item $x1 $x2 $x3) (Item $x1 $x2 $x3))
)
!(add-item 1 2)
!(get-item 1 2)
!(let $item (get-item 1 2)
    (remove-atom &my-space $item)
)
!(get-item 1 2)

the output should be

[()]
[()]
[(Item 1 2 (1, 2)]
[()]
[]

Actual behavior
However, the actual output is

[()]
[()]
[(Item 1 2 (1, 2))]
[()]
[(Item 1 2 (1, 2))]

[vsbogd]

The issue with code above is that (add-atom &my-space (Item $x1 $x2 (py-tuple ($x1 $x2)))) doesn't actually executes py-tuple because add-atom has type (-> Space Atom ()) and its second parameter has type Atom. The reason is add-atom function is intended to add the atom passed without modifying it.

The code can be fixed by using another form of add-atom - add-reduct which evaluates the argument before adding it into a space:

!(bind! &my-space (new-space))

(= (add-item $x1 $x2)
    (add-reduct &my-space (Item $x1 $x2 (py-tuple ($x1 $x2))))
)
(= (get-item $x1 $x2)
    (match &my-space (Item $x1 $x2 $x3) (Item $x1 $x2 $x3))
)
!(add-item 1 2)
!(get-item 1 2)
!(let $item (get-item 1 2)
    (remove-atom &my-space $item)
)
!(get-item 1 2)