Hi, Kevin Ryde <[EMAIL PROTECTED]> writes:
> [EMAIL PROTECTED] (Ludovic Courtès) writes: >> >> I'm not sure the indirection in `scm_init_stacks ()' is needed since it >> uses STACK_LAYOUT for both VTABLE and SCM_STACK_TYPE, > > Not sure what you mean there. We have: VTABLE -> SCM_STACK_TYPE -> stack objects where `x -> y' means "`y' is an instance of `x'". When creating stack objects with (roughly) `(make-struct stack-type)', VTABLE is _not_ consulted at all. The layout of stack objects is determined only by that specified in SCM_STACK_TYPE. Thus, VTABLE is redundant. All this would be clearer if we had a `struct-vtable' type such that `(make-struct struct-vtable)' would yield a new vtable (just like `(make <class>)' yields a new GOOPS class). Like `<class>', `struct-vtable' would terminate the "reflective tower" (i.e., its vtable is itself). Actually, such a `struct-vtable' stealthily appears in `make-vtable-vtable', under the name of REQUIRED_VTABLE_FIELDS: We could really have a `struct-vtable' whose layout is REQUIRED_VTABLE_FIELDS and then `make(-vtable)+' could be simply implemented in terms of `make-struct' (just like `make-class' uses `make'). I guess I should try implementing this theory one of these days. ;-) > At any rate, below is where I'm up to so far with trying to make the > docs a bit easier. It includes my proposed make-vtable. Could be > possible to leave that out, but perhaps those like me who managed to > never understand structs can see if it makes the understanding easier > :-). Thanks for working on this! > A "structure" is a first class data type which holds Scheme values or C > words in slots numbered 0 upwards. A "vtable" represents a structure > type, giving read/write permissions on slots, whether they're Scheme > values or uninterpreted words, and giving an optional print function > for the structure (for use by `write' etc). Perhaps a word saying the struct fields are laid out in a contiguous memory area, which makes interaction with C much easier (using C arrays or some such). > Vtable Vtables > .............. > > As noted above, vtables are structures and such a structure is itself > described by a vtable. Such a "vtable of a vtable" can be created with > `make-vtable-vtable' below and used to build sets of related vtables, > possibly with extra application fields. > > This second level of vtable can be a little confusing. An example, > and indeed a typical use, is Guile's own record system (*note > Records::). Currently record types are implemented as vtables, and > those vtables have an extra slot holding the list of field names for > that type (as passed to `make-record-type'). While the rest looks good, I remain skeptical about this part. And a manual that claims to be confusing does not inspire confidence. ;-) Thanks, Ludovic. _______________________________________________ Guile-devel mailing list Guile-devel@gnu.org http://lists.gnu.org/mailman/listinfo/guile-devel
