On Tue, Feb 11, 2025 at 11:25 PM Alexander Burger <picolisp@software-lab.de>
wrote:
>
> If a problem is a linear operation, like traversing a list, a loop is
> more natural for me. For traversing a tree, recursion is better of
> course.
>
> Thanks!
> (de fiboSwap (N)
> (let (A 0 B 1)
> (do N
> (swap 'B (+ (swap 'A B) B)) ) ) )
>
> That is really cool! Something to keep in mind.
I took a moment to rewrite the tco versions of the swap, mtf, mft functions
I had
using my newly realized understanding of nth, con, conc, insert.... (code
below).
Shorter, simpler, and much! faster on large lists.
: (swappXchg (1 . 7) (1 2 3 4 5 6 7 8 9)) # Swap
-> (7 2 3 4 5 6 1 8 9)
: (mtfConc (1 2 3 4 5 6 7 8 9) 7) # Move to front
-> (7 1 2 3 4 5 6 8 9)
: (mftConc (1 2 3 4 5 6 7 8 9) 7) # Move from top
-> (2 3 4 5 6 7 1 8 9)
/Lindsay
# Swap two elements in a list
(de swappXchg (P L)
(when (and (pair P) (lst? L))
(ifn (> (cdr P) (car P))
(setq P (cons (cdr P) (car P))) )
(let
(Lst L
Lhs (car P)
Rhs (cdr P)
LhsN (nth L Lhs)
RhsN (nth LhsN (inc (- Rhs Lhs))) )
(when (and LhsN RhsN) (xchg LhsN RhsN))
L ) ) )
# Move from top
(de mftConc (X N)
(cond
((and (> N 1) (lst? X))
(let
(Elt (cons (car X))
Lhs (head (dec N) (cdr X))
Rhs (cdr (nth X N)) )
(con Elt Rhs)
(conc Lhs Elt)
Lhs ) )
(T X) ) )
(de mftInsert (X N)
(cond
((and (> N 1) (lst? X))
(insert N (cdr X) (car X)))
(T X)))
# Move to Front
(de mtfConc (X N)
(cond
((and (> N 1) (lst? X))
(let
(Lhs (head (dec N) X)
Rhs (cdr (nth X (dec N)))
Elt (cons (car Rhs)) )
(ifn Rhs
X
(con Elt Lhs)
(conc Elt (cdr Rhs))
Elt ) ) )
(T X) ) )
