Very nice. The Racket special sauce is the (match*...). I need to get my
head around what's going on there.
A.
On Saturday, 18 August 2018 22:52:51 UTC+10, Jens Axel Søgaard wrote:
>
>
>
> Den lør. 18. aug. 2018 kl. 03.31 skrev Andrew J <and...@alphajuliet.com
> <javascript:>>:
>
>> 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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