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1 point by rkts 5848 days ago | link | parent

Because unhygienic macros are a pain in the ass. Surely I'm not the only one who thinks this?


1 point by applepie 5847 days ago | link

Maybe you'd like them more if you called them "macros" instead of "unhygienic macros" ;)

No, really, macros, being essentially compilers, give you enough power to build everything you'd ever want into Lisp, including "hygienic" macros, and even to build facilities to write hof-like things in less painful ways.

Maybe they're a pain in the ass if you don't "go meta", in the same way computers are a pain in the ass if you don't build OSes and compilers first.

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1 point by stefano 5847 days ago | link

The real point in favor of unhygienic macros is that they are less constraining and, personally, I find them easier to write and read than hygienic macros. I don't find a bad idea to have both hygienic macros and unhygienic macros.

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1 point by rkts 5847 days ago | link

Sigh...

Obviously I like unhygienic macros when they are necessary. The problem is, I keep writing higher-order functions and getting tired of typing the "fn" over and over, and then I have to convert the function to a macro, making it twice as long and hard to read. Hygienic macros help, but they still are not as easy to write as plain functions.

I know I'm not the only person who has this problem, but maybe I'm the only one who realizes I have this problem. I see people on the Internet raving about the AMAZING POWER of macros, and most of their examples are just higher-order functions with some small cosmetic changes. Most of the macros in Arc are of the same kind.

I'm not denying that macros are powerful. I just think there is a gross inefficiency in using them where you shouldn't have to, just because of minor syntactic concerns.

I wanted to solve this with a short, clean syntax for function literals, but I haven't been able to come up with one and neither, apparently, has anyone else. So instead I decided to try something that would generate macros out of HOFs.

I thought this would be evident from my post, but apparently it wasn't.

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1 point by shader 5847 days ago | link

Maybe we could use { args | body } ? I don't think the braces are taken.

Now, maybe that's a bad idea; instead, we could redefine the brackets, so that a pipe divides args and body, and if it doesn't have a pipe, it defaults to binding _ ? I don't know how hard that would be, or some variation on the concept, but it would be a bit shorter than (fn (args) (body)), if you don't want to type that all the time.

And how exactly does 'w/hof work, as defined so far? And if it's "standard" now, why not just implement it?

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3 points by almkglor 5847 days ago | link

Since Anarki defines [ ... ] as (make-br-fn ...), it's actually possible to have the syntax:

  [params || body]
Which would be:

  (make-br-fn (params || body))
(The double bar is needed because a single | is reserved for weird symbols)

By simply redefining make-br-fn, you can redefine the syntax of [ ... ] to an extent

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1 point by shader 5847 days ago | link

I wondered if redefining [...] might be possible. It seems to me that the new double bar syntax is practically a super-set of the old one: if it doesn't have the double bar, just treat it like the old bracket function and define _ to be the argument; otherwise use the argument list provided. Including an empty list, I would hope.

Any word on how hard that would be?

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1 point by almkglor 5847 days ago | link

  (let old (rep make-br-fn)
    (= make-br-fn
       (annotate 'mac
         (fn (l)
           (if (some '|| l)
               (do
                 your-stuff)
               (old l))))))
Be careful of supersets: someone's code might unexpectedly break ^^

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1 point by shader 5847 days ago | link

Isn't that to be expected in an evolving open source language :)

Do you think || is the best choice, or something else?

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2 points by rkts 5847 days ago | link

I think it's a bad choice, personally. I'm not crazy about the single pipe either, but || is awful.

Tangent: this may be a dumb question, but do we really need the pipe character for symbols? I know I've never used it. Why not disallow spaces (and the like) in symbols, and free the pipe for new syntax?

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2 points by shader 5847 days ago | link

If you don't like the pipe, then recommend something :)

Other possibilities, in no particular order:

  [ # ]
  [ - ]
  [ = ]
  [ -> ]
  [ : ]
  [ => ]
  [ > ]
  [ ~ ]
  [ % ]
  [ ! ]
  [ $ ]
  [ ^ ]
  [ & ]
  [ * ]
  [ @ ]
  [ + ]
  [ | ]
  [ || ]
  [ ? ]
Most of those are either bad looking or already taken. Anything stand out as a good / ok / not bad choice?

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2 points by almkglor 5846 days ago | link

:, =>, and -> don't look bad.

# can't be redefined

Let's try some mockups:

  [ a b c :
    (/ (+ (- b) (sqrt (+ (* b b) (* 4 a c))))
       (* 2 a))]

  [: (thunk this)]

  [ a b c ->
    (/ (+ (- b) (sqrt (+ (* b b) (* 4 a c))))
       (* 2 a))]

  [-> (thunk this)]

  [ a b c =>
    (/ (+ (- b) (sqrt (+ (* b b) (* 4 a c))))
       (* 2 a))]

  [=> (thunk this)]

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1 point by shader 5832 days ago | link

So, did we ever make a decision about this? Does someone who knows more than I do about this want to implement it?

Also, is there a way to compose or nest these lambda shortcuts? Or would that make this almost impossible to implement?

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1 point by almkglor 5832 days ago | link

Nesting doesn't seem impossible: the reader, I think, will handle nesting as:

  [foo [bar]]

  (make-br-fn (foo (make-br-fn (bar))))
As for implementation, it's easy:

  (given ; this gives us access to the old
         ; implementation of [] syntax; it
         ; is used when we don't find the
         ; separator
         old (rep make-br-fn)
         ; use a variable to easily change
         ; the separator
         separator ': ;for experimentation
    (= make-br-fn
       ; a macro is just a function that has
       ; been tagged (or annotated) with the
       ; symbol 'mac
       (annotate 'mac
         ; the reader reads [...] as
         ; (make-br-fn (...))
         (fn (rest)
               ; find the separator
           (if (some separator rest)
               ; note the use of the s-variant givens
               ; the "s" at the end of the name of givens
               ; means that the variables are specifically
               ; bound in order, and that succeeding variables
               ; may refer to earlier ones
               (givens ; scans through the list, returning
                       ; an index for use with split
                       ; (no built-in function does this)
                       scan
                       (fn (l)
                         ((afn (l i)
                            (if (caris l separator)
                                i
                                (self (cdr l) (+ i 1))))
                          l 0))
                       ; now do the scan
                       i (scan rest)
                       ; this part destructures a two-element
                       ; list
                       (params body)
                         ; used to get around a bug in split
                         (if (isnt i 0)
                             (split rest i)
                             (list nil rest))
                 ; it just becomes an ordinary function
                              ; body includes the separator,
                              ; so we also cut it out
                 `(fn ,params ,@(cut body 1)))
               ; pass it to the old version of make-br-fn
               ; if a separator was not found
               (old rest))))))
Edit: tested. Also reveals a bug in split: (split valid_list 0) == (split valid_list 1)

  (= foo [ i :
           [ : i]])

  ((foo 42))
edit2: p.s. probably not really easy much after all^^. As a suggestion, (help "stuff") is good at finding stuff.

edit3: added comments

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1 point by shader 5832 days ago | link

Hmm. It doesn't seem to work with the older version. If I try ([+ _ 10] 3) it complains: "reference to undefined identifier: ___"

It used to complain "#<procedure>: expects 1 argument, given 3: + _ 10", but something seems to have changed between updates :)

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1 point by almkglor 5832 days ago | link

Have you tried restarting Arc and then repasting the code?

Probably some dirt left from older versions ^^

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1 point by shader 5846 days ago | link

I agree, those aren't bad.

I think that out of those, : makes the most sense. They all make logical sense with arg lists, but : looks the best without any.

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1 point by almkglor 5846 days ago | link

> Tangent: this may be a dumb question, but do we really need the pipe character for symbols? I know I've never used it. Why not disallow spaces (and the like) in symbols, and free the pipe for new syntax?

Wanna start implementing a reader for Arc?

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1 point by rkts 5846 days ago | link

Looks like this is configurable in MzScheme. Do

  (read-accept-bar-quote #f)

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1 point by rkts 5847 days ago | link

How would you write a function with no arguments?

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1 point by shader 5847 days ago | link

leave the part before the pipe empty, I suppose

  {| body}
it might need a space between the brace and the pipe, but I don't know

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