I'm pretty sure we have to do the car/cdr recursion because functions like map and each don't work on pairs, they only work on proper lists and most trees are not proper lists.
I think the obvious problem with that reasoning is it reinforces the notion that map, each, etc. "should" break on dotted lists. Even if that's the case, it's not like ontree & pals couldn't open-code a recursive function that worked on dotted tails; I merely used each/map in my example definitions as a convenience. If you prefer:
; Again, not that this has to replace the standard 'ontree...just can't think
; of a better name.
(def ontree (f expr)
(f expr)
(unless (atom expr)
((afn (subexpr)
(if (atom subexpr)
(and subexpr (ontree f subexpr))
(do (ontree f (car subexpr))
(self (cdr subexpr)))))
expr)))
arc> (ontree prn '(def f (x . xs) (cons nil xs)))
(def f (x . xs) (cons nil xs))
def
f
(x . xs)
x
xs
(cons nil xs)
cons
nil
xs
This versus the standard ontree:
arc> (ontree prn '(def f (x . xs) (cons nil xs)))
(def f (x . xs) (cons nil xs))
def
(f (x . xs) (cons nil xs)) ; <-- this potentially looks like a call to f!
f
((x . xs) (cons nil xs))
(x . xs)
x
xs
((cons nil xs))
(cons nil xs)
cons
(nil xs)
nil
(xs)
xs
nil
nil
On that note, I certainly find myself working around Arc's rampant disregard for dotted lists in my projects:
Note: you can use iff instead of writing a new function whenf
Not in vanilla Arc, I'm afraid. :) And I've always thought Anarki's iff is poorly named, due to the English collision with the "if and only if" abbreviation.
It does seem like a good idea, abstracting as a list of lists instead of a binary tree. The best name I can think of is onlol. I really don't think that we should extend map and each to work on dotted lists, instead we should create other functions treemap and treeach since dotted lists are actually trees and no longer lists.
