Methods for turning objects into sequences.

Struct objects can now define methods car, cdr and nullify.
With these, they can participate in operations on sequences.

* eval.h (car_s, cdr_s): Declared.

* lib.c (nullify_s): New symbol variable.
(car, cdr): Implement for struct objects via, respectively,
their car and cdr methods.
(tolist): Handle objects by mapping through identity.
(nullify): Implement for objects optionally: if an object
is a struct with a nullify method, use it, otherwise go
through default case of just returning the object.
(empty): Implement for objects that have nullify method.
(obj_init): Initialize nullify_s.

* struct.c (maybe_slot): New function.

* struct.h (maybe_slot): Declared.

* txr.1: Documented car, cdr and nullify method
convention.

1 files changed, 1 insertions, 0 deletions

diff --git a/struct.h b/struct.h
index e71f717b..46dc6542 100644
--- a/struct.h
+++ b/struct.h
@@ -39,6 +39,7 @@ val replace_struct(val target, val source);
 val reset_struct(val strct);
 val find_struct_type(val sym);
 val slot(val strct, val sym);
+val maybe_slot(val strct, val sym);
 val slotset(val strct, val sym, val newval);
 val static_slot(val stype, val sym);
 val static_slot_set(val stype, val sym, val newval);