[RMS faults Tcl for its linked-lists-lessness. Explain what linked lists are, who RMS is, and Tcl perspective--mostly that Tcl doesn't need 'em.]
Arjen Markus I do not know who RMS is, but "woe , ye of little imagination", Tcl lists can be used as linked lists - if you regard a linked list as some abstract data structure (apart from the implementation!). I regard his/her statement as an example that most people can not distinguish implementation and concept!
RS RMS is Richard M Stallman, a famous programmer in the GNU scene, but not enthusiastic about Tcl. (See Who says Tcl sucks...) I also have problems understanding the need for linked lists - Tcl's are contiguous in memory, so the benefit of links, i.e. iterating over it, is easily reached with foreach. OTOH, recursing over lists involves copying in Tcl, so real linked lists like LISP's CAR/CDR also have their advantages.
LV I'd say the issue is likely this - people used to algorithmic solutions requiring specific data structures, such as structures, linked lists, etc. find it difficult to envision how to efficiently implement such solutions in Tcl with only flat lists and hash tables.
davidw the real problem is not linked lists in and of themselves, but the lack of references. Linked lists aren't really all that necessary in Tcl for the simple case, but references allow you to easily construct more complex data structures.
Arjen Markus Can this not be achieved in a very similar way as in Scheme (the LISP dialect I am gradually learning because of the SICP book)? For instance:
set complex_data_struct {A {B C {D E {F G}}}Such a structure (lists within lists) allows one to define recursive lists as well:
set recursive_list {A {B {C {D {E {F {G}}}}}}davidw - maybe it's visually similar, but what's going on underneath is not the same. Have a look at this scheme code, and try and accomplish the same thing in Tcl:
> (define a (list 1 2))
> (define b (list 3 4))
> (define l1 (list a b))
> l1
((1 2) (3 4))
> (set-car! b 30)
> l1
((1 2) (30 4))As far as I know, it's not possible. Everything gets turned into a string at some point, so references don't get preserved.
Stephen Trier - back in the dark ages, I wrote LISP-style linked list routines in BASIC that used arrays. The internal pointers were array indexes. One could do the same in Tcl with lset or an array.