lisp change machine

dynamic programming mixed with HOFs. originally an exam question. brain on fire for an undergrad fuckwit like myself

(define (change amt coins)
(cond
((= amt 0) '(()))
((or (<= amt 0) (null? coins)) '())
(else
(fold-right (lambda (a b) (append a b))
'()
(map
(lambda (n)
(map
(lambda (u)
(append (list n) u))
(change (- amt n)
(filter (lambda (k) (>= k n)) coins))))
coins)))))

;; -----------------------------------------------------------------------

(define (display-nl u)
(display u)
(newline))

(define display-elements
(lambda (u)
(map display-nl u)))

(define (demo r k)
(display-nl '-----------------------------)
(display r) (display ';;) (display k) (newline)
(display-nl '=============================)
(display-elements (change r k))
(display-nl '-----------------------------)
(newline))

;; -----------------------------------------------------------------------

(newline)

(demo 5 '(1 2 5))
(demo 13 '(1 3 5 7))
$ ./lisp <change.lisp

Loaded `prefix.txt'

-----------------------------
5;;(1 2 5)
=============================
(1 1 1 1 1)
(1 1 1 2)
(1 2 2)
(5)
-----------------------------

-----------------------------
13;;(1 3 5 7)
=============================
(1 1 1 1 1 1 1 1 1 1 1 1 1)
(1 1 1 1 1 1 1 1 1 1 3)
(1 1 1 1 1 1 1 1 5)
(1 1 1 1 1 1 1 3 3)
(1 1 1 1 1 1 7)
(1 1 1 1 1 3 5)
(1 1 1 1 3 3 3)
(1 1 1 3 7)
(1 1 1 5 5)
(1 1 3 3 5)
(1 3 3 3 3)
(1 5 7)
(3 3 7)
(3 5 5)
-----------------------------

>>36
I don't know of any bigger waste of my time than to master any language according to that definition. To me, mastering the BNF description (of certain kinds of languages) is as good as mastering the language. Implementation quirks should either be standardized or removed from the language.

>>41

To me, mastering the BNF description (of certain kinds of languages) is as good as mastering the language

You're insane.

>>42
he probably means that most languages of the same type are only syntax-change from each other. this is sadly often the case.

>>42

The C grammar fits in like 2-3 pages IIRC in the K&R book. it's not *that* bad

>>1
c-c-cdr c-c-cdr c-c-cdr cdr cdr
c-c-cdr c-c-cdr c-c-cdr cdr cdr
c-c-cdr c-c-cdr c-c-cdr cdr cdr
c-c-cdr c-c-cdr c-c-cdr cdr cdr
c-c-cdr c-c-cdr c-c-cdr cdr cdr
c-c-cdr c-c-cdr c-c-cdr cdr cdr
c-c-cdr c-c-cdr c-c-cdr cdr cdr
c-c-cdr c-c-cdr c-c-cdr cdr cdr
c-c-cdr c-c-cdr c-c-cdr cdr cdr
c-c-cdr c-c-cdr c-c-cdr cdr cdr
c-c-cdr c-c-cdr c-c-cdr cdr cdr
c-c-cdr c-c-cdr c-c-cdr cdr cdr

>>41
I SAY WE STANDARDISE DA STANDARD, LET THE FAT CATS GET WHAT'S COMING TO THEM, YA FUCKIN STAK BOI RETOID

Lisp change machine? that's called a hammock my friend. Rich Hickey showed us the way. We need to join him and change lisp, and with it, the world.

>>47
kek

>>48
/polecat kebabs/

>>47
I made a change machine in Haskell with the Obama monad.

>>50
Well you failed, because it didn't give me the rest of my money back.