structs: improve access to initfun and postinitfun.

In this change, a struct type's initfun and postinitfun
become mutable. This is achieved by modeling them as
the pseudo-static-slots :initfun and :postinitfun.
Effectively these now behave as reserved names which do not
denote static slots but these special functions.

* eval.c (lookup_fun): When (meth type slot) syntax is
encountered, treat the slot names :init and :postinit
specially: retrieve these special functions instead of
accessing static slots.

* share/txr/stdlib/place.tl (sys:get-fun-getter-setter):
Similarly, when handling (meth type slot) syntax, return
the alternative getter/setter functions for the special
functions, not the static slot accessing functions.
Also, getting rid of a useless @1 here in existing code,
since (op foo @1) is equivalent to (op foo).

* share/txr/stdlib/struct.tl (sys:defmeth): Check for
the special names :init and :postinit, handling these
through the appropriate setter functions rather than
static-slot-ensure.

* struct.c (init_k, postinit_k): New keyword symbol variables.
(struct_init): Initialize init_k and postinit_k. Register
intrinsics struct-get-initfun, struct-set-initfun,
struct-get-postinitfun and struct-set-postinitfun.
* (struct_get_initfun, struct_set_initfun,
struct_get_postinitfun, struct_set_postinitfun): New
functions.
(method_name): For each struct type visited, check
whether the function is the initfun or postinitfun
and return the appropriate meth syntax if so.

* struct.h (init_k, postinit_k, struct_get_initfun,
struct_set_initfun, struct_get_postinitfun,
struct_set_postinitfun): Declared.

* txr.1: Documented. Updated description of method-name,
defmeth, and documented new functions.

1 files changed, 8 insertions, 2 deletions

diff --git a/eval.c b/eval.c
index 0a6940eb..679b12aa 100644
--- a/eval.c
+++ b/eval.c
@@ -486,8 +486,14 @@ val lookup_fun(val env, val sym)
         val type = or2(find_struct_type(strct),
                        if2(lisplib_try_load(strct),
                          find_struct_type(strct)));
-        return if2(and2(type, static_slot_p(type, slot)),
-                   cons(sym, static_slot(type, slot)));
+        if (slot == init_k) {
+          return cons(sym, struct_get_initfun(type));
+        } else if (slot == postinit_k) {
+          return cons(sym, struct_get_postinitfun(type));
+        } else {
+          return if2(and2(type, static_slot_p(type, slot)),
+                     cons(sym, static_slot(type, slot)));
+        }
       } else if (car(sym) == macro_s) {
         return lookup_mac(nil, cadr(sym));
       } else if (car(sym) == lambda_s) {