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#lang racket
(provide get-lines
enumerate
repeat
split-list-by
transpose-list)
(define (repeat n e)
(let loop ((i 0) (ret '()))
(if (>= i n)
ret
(loop (+ 1 i) (cons e ret)))))
(define (trim-lines lines)
(if (= 0 (string-length (car lines)))
(trim-lines (cdr lines))
lines))
(define (get-lines fp)
(define lines
(let loop ((lines '()))
(define l (read-line fp))
(if (eof-object? l)
(reverse lines)
(loop (cons l lines)))))
(reverse (trim-lines (reverse (trim-lines lines)))))
(define (enumerate lst)
(let loop ((i 1) (ret '()) (remain lst))
(if (null? remain)
(reverse ret)
(loop (+ 1 i) (cons (list (car remain) i) ret) (cdr remain)))))
(define (split-list-by e lst . eq)
(define cmp (if (null? eq) equal? eq))
(let loop ((ret '())
(cur '())
(lst lst))
(if (null? lst)
(reverse (cons (reverse cur) ret))
(if (cmp e (car lst))
(loop (cons (reverse cur) ret) '() (cdr lst))
(loop ret (cons (car lst) cur) (cdr lst))))))
(define (transpose-list lines)
(define width (string-length (car lines)))
(define new-lines (make-vector width))
(let loop ((i 0))
(if (>= i width)
(vector->list new-lines)
(let ()
(define char-list (map (λ (l) (string-ref l i)) lines))
(vector-set! new-lines i (list->string char-list))
(loop (+ i 1))))))
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