My ultimate goal is to get a list of all the words in a file in
order. I have a function that will get a list of all the words on one
line of this file in order, and I want to efficiently concatenate
these lists to end up with one large list. I'm working with about
12000 lines right now, but in a perfect world I'd like to scale much
higher.
I started off just using concat. Basically my code looks like:
(defn getstrlist
([file]
(loop [x (getline file) worklst '()]
(if x
(recur (getline file) (concat worklst (splitstr x)))
worklst))))
Then in the REPL, if I type (def a (getstrlist FILE)), it works fine.
But if I try to output a or take (first a), I get a stack overflow
error. I don't know why this is. I remember hearing somewhere that
Clojure had lazy sequences, so my best guess is that it isn't actually
concatenating anything, but is storing pointers to the start of all
the lists on a stack that overflows when I try to evaluate one of
these pointers.
I know in Scheme I would write this using metalists that keep track of
the location of their last element:
(define (concat metalst1 metalst2)
(set-cdr! (car metalst1) (cdr metalst2))
(set-car! metalst1 (car metalst2))
metalst1)
(define (make-metalst lst)
(cons (get-end lst) lst))
(define (get-end lst)
(if (null? lst)
'()
(if (null? (cdr lst))
lst
(get-end (cdr lst)))))
Which would be fairly efficient. But since Clojure doesn't seem to
have real lists, I'm not quite sure how I could port this over. I
suppose I could implement my own cons pairs like an idiot and do all
of this manually, but I figure I'm just not understanding the "Clojure
solution" to this problem.
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