hy.errors.HyWrapperError: Don't know how to wrap <class …>

[wrobell]

Please consider the following script

(eval-when-compile
  (import dataclasses [dataclass])

  (defclass [dataclass] Column []
    #^str name
    #^str type)

  (defn f-column [name type] (Column name type)))

(defmacro m-create [name type] (f-column name type))
(print (m-create "help" "text"))

Running it I am getting the error

expanding macro m-create
  hy.errors.HyWrapperError: Don't know how to wrap <class 'm-test.Column'>: Column(name=hy.models.String('help'), type=hy.models.String('text'))

Any suggestions now to deal with this?

[Kodiologist]

As the error message implies, you've written a macro that returns a Column object. It's hard for me to see what Hy code a Column object should correspond to, so I'm not sure what you expected.

[wrobell]

I am writing something more complex, and I got such error. The example here is just to replicate the error I am getting.
I would expect the macro to create the object. Nothing more. What am I missing?

[Kodiologist]

The macro does create the object. At compile-time, when it's expanded. And then it tries to make source code (more specifically: a Hy model) out of that object, which it sounds like isn't what you want. Remember that fundamentally, a macro is code for generating code.

[wrobell]

Got it.. I hope ;)
How can I change function f-column to generate the model to create that object on execution?

[Kodiologist]

Quasiquoting is usually the easiest way to do it.

[wrobell]

Thanks. For other lost souls

(import dataclasses [dataclass])
(defclass [dataclass] Column []
  #^str name
  #^str type)

(eval-when-compile
  (defn f-column [name type] `(Column ~name ~type)))

(defmacro m-create [name type] (f-column name type))
(print (m-create "help" "text"))