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