How to enforce types for a struct/class?

[bistace]

Hello,

I just started learning Gerbil and I would like the compiler to enforce the types of the slots in one of my class. As an example, in the following class I would like to enforce x being a number and y a boolean:

(defclass Foo (x y))

I searched the docs and found the page about contracts but I have a hard time figuring out which syntax I should use in my case and nothing I tried worked. Could you please point me in the right direction?

[vyzo]

You can already attach contracts/types to slots, it is just not documented yet.

So you can write (defclass Foo ((a : some-type) (b : some-other-type))) and so on, with any contract declaration.

The generated constructor and mutators will then enforce the type.

[bistace]

Thank you for your answer! Is there somewhere in the docs where I can find standard types currently implemented?

[bistace]

Sorry to bother you again with my beginner questions but I cannot figure out how to apply this to an actual example. Here is some definition of a class that seems to not be what I should do:

(defclass MyClass ((x : integer) (y : integer)))

Running this into gxi returns the following error:

*** ERROR --
*** ERROR IN (stdin)@1.1-1.49
--- Syntax Error at (expand top): invalid signature; unknown type
... form:   (defclass MyClass ((x : integer) (y : integer)))
... detail: integer at (stdin)@1.25-1.32

Doing this when MyClass has only one slot does not throw an error but the type of x is not checked, as the following code is executed without any problem:

(import :std/contract)

(defclass MyClass (x : integer))

(def (main . args)
  (def c (MyClass x: "test"))
  (displayln c))

Could you please point me in the right direction once again?

[vyzo]

the type is :integer

[vyzo]

all the MOP builtin types are prefixed with :.

[vyzo]

Also, you dont need to import :std/contract any more, contracts are part of the core prelude now.

[bistace]

That works, thanks a lot again!

If someone sees this in the future and wonders what the working code is, here it is:

(defclass MyClass ((x : :integer) (y : :real)))

(def (main . args)
  (def c (MyClass x: 42 y: 30.2))
  (displayln c))