Den lør. 18. aug. 2018 kl. 03.31 skrev Andrew J <and...@alphajuliet.com>:
> Hi. In a little side project, I'm looking for an simple Racket-y way to
> transform a bulleted list into a tree structure, maybe like sxml.
>
> As an example, this...
>
> - a
> - b c
> - d e f
> - g h
>
> would get transformed into something like this...
>
> '(a (b c) (d e f (g h)))
>
> I can see a few ways to do this, from recursively counting indents, right
> through to making a mini DSL (à la *Beautiful Racket*), but I'm wondering
> what a minimal idiomatic solution might look like?
>
>
>
Here is how I would write it.
#lang racket
(define (non-empty-string? s)
(not (string=? s "")))
(define (string->lines s)
(filter non-empty-string?
(regexp-match* #rx"[^\n]*" s)))
(define (indentation-level s)
(for/first ([c s] [i (in-naturals)] #:unless (char=? c #\space))
i))
(define (string->symbols s)
(for/list ([x (in-port read (open-input-string s))])
x))
(define (strip-dash xs)
(rest xs))
(define (bullet-string->nested-list s)
(define lines (string->lines s))
(define levels (map indentation-level lines))
(define symbols (map strip-dash (map string->symbols (string->lines s))))
(define (build js xss)
(match* (js xss)
[('() _) '()]
[((list j) (list xs)) xs]
[((list* i j js) (list* xs xss)) (cond
[(= i j) (cons xs (list (build
(cons j js) xss)))]
[(< i j) (append xs (list (build
(cons j js) xss)))]
[else (error 'build "not proper
nesting")])]))
(build levels symbols))
(bullet-string->nested-list "
- g h")
(bullet-string->nested-list "
- g h
- i j")
(bullet-string->nested-list "
- d e f
- g h")
(define example
"- a
- b c
- d e f
- g h")
(bullet-string->nested-list example)
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