General-purpose libraries for Arc, JavaScript, and Racket.
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Lathe is meant to be a collection of utility libraries that don't
really have a specific purpose other than to make their host language
smoother to program in (at least according to one opinion). In
particular, I'm starting it up so that I have somewhere to post little
things I'm doing in Arc, so that I can talk about them at the Arc
forum ( Other languages are not

Right now, this contains:

  - a very young Arc module system based on renaming of global
      variables (arc/modules/);

  - a young multimethod system built up within that module system

  - a continuation-based backtracking library (arc/amb.arc);

  - an extensive continuation-free, combinator-style iterator library
      which nevertheless supports continuation-based, coroutine-style
      iterator specification as well, as long as the language
      implementation supports it (arc/iter.arc);

  - some more general-purpose modules the multimethod system relies on
      (arc/rules.arc and arc/utils.arc);

  - an updated version of Andrew Wilcox's 'extend macro so that
      extensions can be removed and replaced (arc/extend.arc); and

  - very small examples of using the module system, the multimethod
      framework, and the iteration library in application code
      (arc/examples/), which double as the only test cases to date.

The examples (and therefore the tests) don't cover everything Lathe
has to offer. The code is fairly well commented, so reading those
comments is probably one of the best ways to get a good feel for

== Setup in Arc ==

The code in the arc/ directory is targeted mainly at Arc 3.1, which
you can download at Arc 3.1
itself depends on Racket, which you can get from For more detailed help setting up Arc 3.1,
including how to adjust it to work on Windows,
is a good resource. If you're just getting started with Arc, and list
some other helpful links.

Including stock Arc 3.1, Lathe supports six Arc setups altogether:

  - Arc 3.1, the official Racket implementation

  - Anarki, a community fork of Arc 3.1 (

  - Andrew Wilcox's ar, a fork of Arc 3.1 (

  - Pauan's ar, a fork of Andrew Wilcox's ar

  - Rainbow, a JVM implementation

  - Jarc, a JVM implementation (

To load the core Lathe libraries, run the following code (here
assuming you put the contents of the Lathe arc/ folder into lib/lathe/
in your Arc setup):

  (= lathe-dir* "lib/lathe/")
  (load:+ lathe-dir* "loadfirst.arc")

The lathe-dir* global variable is necessary; the loadfirst.arc code
uses it to determine where to load other Lathe files from.

This code can be pasted into a REPL. Alternately, if you're using
Arc 3.1 or Anarki, it can be placed in your libs.arc.

If you want to use a Lathe module, you can do this:

  (use-rels-as ut (+ lathe-dir* "utils.arc"))

This will set 'ut to a namespace from which you can access all the
things defined in utils.arc. A Lathe namespace is just a macro that
associates friendly symbols with less friendly global names, and you
can use a namespace as follows:

  ; function calling with ( ...)
  (ut.foldl (fn (a b) (+ (* 10 a) b)) 0 '(1 2 3))
  ; macro usage with (ut:foo ...), which also works for function calls
  (ut:foldlet a 0
              b '(1 2 3)
    (+ (* 10 a) b))
  ; using lookup somewhere other than function position
  (iso (flat:map ut.tails (ut:tails:list 1 2 3))
       '(1 2 3  2 3  3
                2 3  3
  ; using as a settable place
  (= old-tails ut.tails
     ut.tails [do (prn "DEBUG: entering utils.arc's 'tails")
  ; lookup of unevaluated global names with ut!foo
  (mac afoldl (aval bval . body)
    `(,ut!foldlet a ,aval b ,bval ,@body))

If you're making an Arc application that uses Lathe libraries, that
should be enough to get started, but you may need to dig through some
code to find the utilities you actually want to import this way.

If instead you're making a library, then you can continue using
'use-rels-as like this, but as long as you're using Lathe already,
you might consider making your library into a module. That's outside
the scope of this readme, but you should get a good idea of what Lathe
modules look like once you've looked at the source of a few of the
modules included with Lathe.

== Setup in Racket ==

Racket is a bit easier to set up. It already has a module system, so
you can import a Lathe module like so:

  (require "your/path/to/lathe/racket/utils.rkt")
  (require (for-syntax "your/path/to/lathe/racket/utils.rkt"))

In fact, utils.rkt is all the Racket support there is for now. It's
not especially exciting, either; PLaneT has two or three other,
significantly more well-developed utility libraries, and I don't have
any frameworks to set me apart from the crowd. In fact, what I do have
largely disregards or works against frameworks that are already built
into Racket! Use it at your own peril, or figure out some way to use
Arc in your Racket program instead.

== Setup in JavaScript ==

Take a peek inside the js/ directory. That's right, Lathe's JavaScript
utilities are all in one file, lathe.js. Minify it as you wish, just
as long as you stay true to the license.

The utilities in lathe.js represent the ones I've found most
interesting from the Arc utilities. The JavaScript version of Lathe is
probably the most well-groomed selection of Lathe utilities right now.
Just watch out for JavaScript's lack of macros! ^_^

== Afterword ==

Thanks a lot for considering Lathe, and I hope it helps you out!

2010, 2011 Ross Angle