RE: custom type tests

["Drew Adams" <drew.adams@oracle.com>]

> >> Does anyone know of code that deals with custom types
> >> in such a way that you could test whether the type of
> >> a user option is compatible with a given type?
> >>
> >> For instance, if a variable `foo' is of type `regexp'
> >> and `bar' is of type `color', I would want a test for
> >> compatibility with type `string' to return non-nil for
> >> each, since a regexp and a color are strings.
> >>
> >> As another example, if `foo' is of type `string', I
> >> would want a test for compatibility with type (choice
> >> (const nil) string) to return non-nil, since a string
> >> is in the union of all strings and {nil}.
> >>
> >> Any existing code that deals with subtypes this way?
> >> Any code that deals with custom type tests, other than
> >> just `custom-variable-type' and (get __ 'custom-type)?
> >>
> >> I'm looking for code that would allow flexible type
> >> tests - subtyping, if possible (see above), but also
> >> not differentiating between types such as (choice
> >> (const :tag "toto" nil) string) and (choice
> >> (const nil) string) or between (choice (choice (const
> >> nil) string) and (choice string (const nil)).
> >>
> >> Any pointers to pertinent code or doc are appreciated.
> >> Think of it this way: Given a custom type, how can I
> >> find all user options that have that type (or a
> >> compatible type, such as a subtype)?
> >
> > I do not know exactly, but the :match property of a
> > widget has the function you need. Look in cus-edit.el
> > and wid-edit.el how this function is built. It does
> > not look very easy to find out however.
>
> Thinking about it again, the code is in set-variable.
> Look for :match there.

Thanks for checking and replying.

No, I don't see that, however. That code is about checking that a given
value is of the right type.

I want to compare two types themselves, to see if they are compatible (one
is <= the other). I don't want to check the type of a value.

I want to know if the custom types defined for two variables are compatible:
whether the type defined for var1 is compatible with the type defined for
var2. If the type of var1 is `regexp' and the type of var2 is `string', for
example, then the types are compatible (var1's type <= var2's type) -
regardless of the current values. Testing current values is not sufficient.

It's really what I said before:

> >> Given a custom type, how can I find all user options that
> >> have that type (or a compatible type, such as a subtype)?

By "have that type", I meant "are defined with that type", not "have values
of that type".