* fix: don't instantiate dummy fields for external types
For ANSI C compatibility reasons, we add a dummy field for memberless
types defined in Carp (see commit 59ef5bbf2b). When registering a type
with no fields, `(register-type A [])`, we'd also attempt to set our
dummy field in the Carp generated initializer for the type. However, the
registered type is totally opaque from the perspective of Carp, and we
can't assume it has a field corresponding to our dummy field.
This commit changes our handling of __dummy in initializers to avoid
setting it for registered types.
* feat: automatically implement str and prn for registered types
This commit makes the auto-generated str and prn functions for
registered types implement the str and prn interfaces, removing the need
for users to call implements on these functions explicitly.
It alters the signature of `autoDerive` in Primitives.hs slightly to
make it more flexible (since registered types have no delete or copy
functions that we can add to the implementation lists of these
interfaces).
* docs: add docs on register-type to CInterop.md
The new documentation clarifies the usage of `register-type` and accounts
for the changes in the prior two commits.
* fix: fix function signatures for generic memberless initers
Filter out dummy field arguments.
* docs: Add details about type name overrides to CInterop.md
* docs: clarify that users can implement delete for registered types