Arc Forum | perhaps a js macro could allow a better syntax?I don't know if macros can do thi...

Arc Forum

1 point by hasenj 5208 days ago | link | parent

perhaps a js macro could allow a better syntax?

I don't know if macros can do this,

    (js
        (jQuery "#content"
            (toggle))        ;; translates to: jQuery("#content").toggle();
        (jQuery ".cue"
            (html "done")
            (addClass "t"))) ;; translates to: jQuery(".cue").html("done").addClass("t");

2 points by rocketnia 5207 days ago | link

Here's the start of an approach loosely influenced by that:

  (def jquery-dedot (symbol)
    (when (isa symbol 'sym)
      (zap string symbol)
      (when (begins symbol ".")
        (cut symbol 1))))
  
  (def parse-chain (chain)
    (whenlet (first-method-sym . rest) chain
      (iflet first-method jquery-dedot.first-method-sym
        (let numargs (or (pos jquery-dedot rest) len.rest)
          (let (first-args rest) (split rest numargs)
            (cons (cons first-method first-args) parse-chain.rest)))
        (err:+ "A chain given to 'parse-chain didn't start with a "
               "dot-prefixed method name."))))
  
  (mac jquery (selector . chain)
    (let result `(js-call js-var!jQuery ,selector)
      (each message parse-chain.chain
        (zap [do `(js-send ,_ ,@message)] result))
      result))
  
  (def js-var (name)
    (annotate 'rendered-js
      string.name))
  
  (def js-call (callee . args)
    (annotate 'rendered-js
      (+ "(" tojs.callee "(" (intersperse "," (map tojs args)) "))")))
  
  (def js-send (object method . args)
    (annotate 'rendered-js
      (+ "(" tojs.object "[" tojs.method "]("
         (intersperse "," (map tojs args)) "))")))
  
  (def tojs (value)
    (caselet type-value type.value
      rendered-js  rep.value
      int          string.value
      string       (do (zap [subst "\\\\" "\\" _] value)
                       (zap [subst "\\'" "'" _] value)
                       (zap [subst "<'+'/" "</" _] value)
                       (zap [subst "]]'+'>" "]]>" _] value)
                       (zap [+ "('" _ "')"] value)
                       (tostring:w/instring stream value
                         (whilet char readc.stream
                           (let code int.char
                             (if (<= 32 code 127)
                               pr.char
                               (let hex (coerce code 'string 16)
                                 (pr "\\u")
                                 (repeat (- 4 len.hex) (pr #\0))
                                 pr.hex))))))
        (err:+ "A value of type \"" type-value "\" can't be "
               "translated by 'tojs (yet).")))

In action:

  arc> (jquery "#content" .toggle)
  #(tagged rendered-js "((jQuery(('#content')))[('toggle')]())")
  arc> (jquery ".cue" .html "done" .addClass "t")
  #(tagged rendered-js "(((jQuery(('.cue')))[('html')](('done')))[('addClass')](('t')))")

This code isn't necessarily shorter than the JavaScript code, but it's set up so that you can conveniently compute parameters from the Arc side via things like (jquery "#blah" .height (- full-height top-height)) while also being able to compute them naturally from the JavaScript side via things like (jquery "#nav" .height (jquery "#content" .height)).

One downside is all the parentheses this leaves. But if that turns out to be a problem, the thing I'd do is to rewrite the JavaScript-generating utilities to return meaningful AST objects rather than just tagged strings. That way, the AST can be pretty-printed in a separate step, once the context of each and every JavaScript expression is known.

An AST could also be good for displaying as debug output, minifying, verifying, compiling, translating to multiple programming languages, and doing any other kind of inspection. The format of the AST could also be set up to make it easier for different generated parts to avoid tripping over each other; for instance, there could be scopes for element IDs or a library dependency resolver.

I just finished converting my website's static site generator to Arc and Penknife (a language I've been making), and I'm using this kind of AST approach, if only 'cause HTML ASTs are so simple. :-p I haven't had the need to generate JavaScript or PHP yet--and I don't even use any PHP right now, lol--but I expect to get around to that someday, and at that point things'll get kinda interesting.

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