SVG: The Good, the Bad and the Ugly

Re:SVG: The Good, the Bad and the Ugly by kazinator on Friday February 12, 2021 @12:52PM (#26116405)

You probably mean

  (path d M 10 10 H 90 V 90 H 10 L 10 10)

Shore up some nesting for the commands with pattern matching, returning a path struct:

  This is the TXR Lisp interactive listener of TXR 251.
  Quit with :quit or Ctrl-D on an empty line. Ctrl-X ? for cheatsheet.
  Garbage collection is on Tuesdays: bring unwanted pointers to curb by 7:30.
  1> (defstruct path () name args)
  #<struct-type path>
  2> (defun parse-path-args (args)
       (match-case args
         ((M @x @y . @rest) ^((M ,x ,y) ,*(parse-path-args rest)))
         ((L @x @y . @rest) ^((L ,x ,y) ,*(parse-path-args rest)))
         ((H @x . @rest) ^((H ,x) ,*(parse-path-args rest)))
         ((V @x . @rest) ^((V ,x) ,*(parse-path-args rest)))
         (())
         (@else (error "bad path arguments: ~s" else))))
  parse-path-args
  3> (defun-match parse-path
       (((path @(symbolp @name) . @args))
        (new path name name args (parse-path-args args)))
       ((@else) (error "bad path syntax: ~s" else)))
  parse-path
  4> (parse-path '(path d M 10 10 H 90 V 90 H 10 L 10 10))
  #S(path name d args ((M 10 10) (H 90) (V 90) (H 10) (L 10 10)))

Error cases:

  5> (parse-path '(path d M 10 10 H 90 V 90 X 10 L 10 10))
  ** bad path arguments: (X 10 L 10 10)
  ** during evaluation of form (error "bad path arguments: ~s"
                                    else)
  ** ... an expansion of (progn (error "bad path arguments: ~s"
                                     else))
  ** which is located at expr-2:2
  ** run with --backtrace to enable backtraces
  6> (parse-path '(paath d M 10 10 H 90 V 90 X 10 L 10 10))
  ** bad path syntax: paath d M 10 10 H 90 V 90 X 10 L 10 10
  ** during evaluation of form (error `bad path syntax: @else`)
  ** ... an expansion of (progn (error `bad path syntax: @else`))
  ** which is located at expr-3:1
  ** run with --backtrace to enable backtraces

[ Parent | on HN ]

Re:SVG: The Good, the Bad and the Ugly by dan-robertson on Friday February 12, 2021 @04:26PM (#26118727)

I think that’s too flat. There’s no easy place to put the width and suchlike. I think you’d want something like:

  (path (M 10 10 H 90 V 90 H 10 L 10 10) :color red)

Though probably I would prefer something more nested if possible, so you have a list of instructions rather than needing to parse them out of a flattened list. And I would likely use an alist rather than a plist for attributes like colour or stroke width.

[ Parent | on HN ]