Clojure macros continue to surprise me (opens in new tab)

(tonsky.me)

138 pointsjgrodziski1y ago27 comments

27 comments

I really enjoyed reading this, and I don't know Clojure at all. This is a problem I've encountered several times while building design systems/component libraries. It's a very universal documentation problem, regardless of what platform it's targeting.

I have done the same with React - but it gets messy. Something nice like in the post would be great for that.

Too often I see very poor Storybook sites in the wild (a web based design system visual explorer, somewhat like the screenshot in the post) where no thought was given to this exact problem.

Instead of something meaningful like in the post, I see:

    () => <TextInputStorybook />

As the only avaliable code. The point of the code blocks is so people can copy paste. When I see that, I know I'm in for a rough ride because the code quality inevitably isn't any good either.

For reference, this is easily the best design system I know of: https://seek-oss.github.io/braid-design-system/components/Te... I use this as a reference when I work on my own.

josefrichter1y ago

In elixir you can run docs as (init) tests too. The doctest macro is generating the tests from the docs within the module. Maybe this might be interesting together with this article.

seancorfield1y ago

The fifth time this has been posted in just over a week... it must be a REALLY good article! :)

seancorfield1y ago

My bad... the sixth time (the fifth time was under a different title).

kazinator1y ago

> What if our macro read the source file?

> Like, actually went to the file system, opened a file, and read its content? We already have the file name conveniently stored in file, and luckily Clojure keeps sources around.

> So this is what I ended up with:

> (defn slurp-source [file key]

Looks like a function to me (which is good).

chii1y ago

it can't be a function because the source is only guaranteed to be available at compile time, rather than at runtime.

kazinator1y ago

It's reading code from a file, which you can make arrangements for to be there at any time you want.

Files are not directly relevant to macros.

The code that a macro invocation has access to by design is the datum which comprises that invocation itself. That may have come from an expression in a file, and may be annotated in some way with the location info. Other than that, macros do not necessarily have access to their textual source code. No such thing necessarily exists because macros can be invoked by code that was generated (possibly by other macros or in other ways) and so never existed as characters in a file.

I don't have a clear picture of the architecture of the system that the article refers to, but the author presents, as his end result, a defn form, which defines a function and not a macro.

If a macro is needed to get that function to be called at compile time, that would be a minor hooking detail, and not an instance of a macro being used to perpetrate a complex code transformation. The function just needs a file name and a string.

(It looks as if the author's system may be interactive; the code files are there all the time and can be changed, and he wants the view of the files to refresh?)

lispm1y ago

It could be a helper-function which gets called by a macro expansion at compile-time. One would define the feature as a function which is available at compile-time and the macro calls it during expansion.

phoe-krk1y ago

A macro is a perfectly normal function. It's simply called at compile time, with its contents as its argument.

1 more reply

compacct271y ago

The real trick here is dodging ASTs, which, after trying to use in so many parse-the-code projects, really aren’t needed all the time but are put pretty highly on the pedestal

layer81y ago

An AST can carry the original source representation on each node as metadata — best of both worlds.

simply-typed1y ago

  sometimes a vector is just a vector, but sometimes it’s a UI component and shows the structure of the UI.

Easily the worst aspect of Clojure. Everything is an untyped map or an untyped vector. Your editor can't tell the difference between a vector of keywords and some DSL for a macro. Things like this make Clojure a nightmare to refactor and scale poorly relative to languages like TypeScript.

geokon1y ago

Thankfully this hiccup style seems less common in recent code. ie. where the index in the vector has a hidden meaning.. Now vectors are typically used for array of the same datatype. I think this makes more sense as basically if you see a vector, you can shove it in to map/filter/etc.

People now prefer using maps - even if it's a bit more verbose. Not sure why records fell out of fashion. You get the terseness of hiccup and the named keys of maps

pjmlp1y ago

Just wait for using full blown CL macros then.

packetlost1y ago

CL macros are more or less the same as Clojure macros and neither hold a candle to modern Scheme or Racket macros :)

BoingBoomTschak1y ago

Eh? Pretty sure they're more powerful. And readable, unlike the Scheme ones that look as elegant and well integrated as a caravan being pulled by a Porsche =).

2 more replies

kazinator1y ago

TXR Lisp:

  $ cat slurp-source.tl
  (defun slurp-source (path key)
    (let* ((lines (file-get-lines path))
           (match (member-if (op contains key) lines))
           (tail (rest match))
           (indent (find-min-key tail : (op match-regex @1 #/\s*/)))
           (dedent (mapcar (op drop indent) tail)))
      `@{dedent "\n"}\n`))
  $ txr -i slurp-source.tl
  1> (put-string (slurp-source "slurp-source.tl" "let*"))
       (match (member-if (op contains key) lines))
       (tail (rest match))
       (indent (find-min-key tail : (op match-regex @1 #/\s*/)))
       (dedent (mapcar (op drop indent) tail)))
  `@{dedent "\n"}\n`))
  t

fithisux1y ago

Wow!

j / k navigate · click thread line to collapse

27 comments

lloydatkinson1y ago

I have done the same with React - but it gets messy. Something nice like in the post would be great for that.

Too often I see very poor Storybook sites in the wild (a web based design system visual explorer, somewhat like the screenshot in the post) where no thought was given to this exact problem.

Instead of something meaningful like in the post, I see:

    () => <TextInputStorybook />

As the only avaliable code. The point of the code blocks is so people can copy paste. When I see that, I know I'm in for a rough ride because the code quality inevitably isn't any good either.

For reference, this is easily the best design system I know of: https://seek-oss.github.io/braid-design-system/components/Te... I use this as a reference when I work on my own.

josefrichter1y ago

In elixir you can run docs as (init) tests too. The doctest macro is generating the tests from the docs within the module. Maybe this might be interesting together with this article.

seancorfield1y ago

The fifth time this has been posted in just over a week... it must be a REALLY good article! :)

seancorfield1y ago

My bad... the sixth time (the fifth time was under a different title).

kazinator1y ago

> What if our macro read the source file?

> Like, actually went to the file system, opened a file, and read its content? We already have the file name conveniently stored in file, and luckily Clojure keeps sources around.

> So this is what I ended up with:

> (defn slurp-source [file key]

Looks like a function to me (which is good).

chii1y ago

it can't be a function because the source is only guaranteed to be available at compile time, rather than at runtime.

kazinator1y ago

It's reading code from a file, which you can make arrangements for to be there at any time you want.

Files are not directly relevant to macros.

I don't have a clear picture of the architecture of the system that the article refers to, but the author presents, as his end result, a defn form, which defines a function and not a macro.

(It looks as if the author's system may be interactive; the code files are there all the time and can be changed, and he wants the view of the files to refresh?)

lispm1y ago

phoe-krk1y ago

A macro is a perfectly normal function. It's simply called at compile time, with its contents as its argument.

1 more reply

compacct271y ago

The real trick here is dodging ASTs, which, after trying to use in so many parse-the-code projects, really aren’t needed all the time but are put pretty highly on the pedestal

layer81y ago

An AST can carry the original source representation on each node as metadata — best of both worlds.

simply-typed1y ago

  sometimes a vector is just a vector, but sometimes it’s a UI component and shows the structure of the UI.

geokon1y ago

People now prefer using maps - even if it's a bit more verbose. Not sure why records fell out of fashion. You get the terseness of hiccup and the named keys of maps

pjmlp1y ago

Just wait for using full blown CL macros then.

packetlost1y ago

CL macros are more or less the same as Clojure macros and neither hold a candle to modern Scheme or Racket macros :)

BoingBoomTschak1y ago

Eh? Pretty sure they're more powerful. And readable, unlike the Scheme ones that look as elegant and well integrated as a caravan being pulled by a Porsche =).

2 more replies

kazinator1y ago

TXR Lisp:

  $ cat slurp-source.tl
  (defun slurp-source (path key)
    (let* ((lines (file-get-lines path))
           (match (member-if (op contains key) lines))
           (tail (rest match))
           (indent (find-min-key tail : (op match-regex @1 #/\s*/)))
           (dedent (mapcar (op drop indent) tail)))
      `@{dedent "\n"}\n`))
  $ txr -i slurp-source.tl
  1> (put-string (slurp-source "slurp-source.tl" "let*"))
       (match (member-if (op contains key) lines))
       (tail (rest match))
       (indent (find-min-key tail : (op match-regex @1 #/\s*/)))
       (dedent (mapcar (op drop indent) tail)))
  `@{dedent "\n"}\n`))
  t

fithisux1y ago

Wow!

j / k navigate · click thread line to collapse