Rus^3

Ruby with Syntax Sugar of Scheme. Or a simple translator from Scheme program to Ruby.

Execute as:

> gem install rus3

You can start the Rus3 REPL with the command, rus3.

> rus3
A simple REPL to run Rus3:
Rus3(scheme)>

Rus3(scheme)> is the prompt of the Rus3.

In the REPL, you can enter Scheme expressions. The REPL reads your Scheme expressions, translates it to Ruby expressions, and evaluated them. Then, the REPL prints the result after ==> .

If you want to run verbosely, use "-d" (or "--debug") option, then it will become very verbose:

A simple REPL to run Rus3:
(rus3 :version 0.2.0 :release 2021-05-02
  (repl :version 0.2.0
    (parser-module :version 0.2.0 ((scheme-parser :version 0.2.0) (scheme-lexer :version 0.2.0)))
    (evaluator-module version: 0.2.0 ((scheme-evaluator :version 0.2.0) (scheme-ruby-translator :version 0.1.0)))
    (:using :built-in :printer)))
Rus3(scheme)>

Boolean (#f and #t), an empty list (()), a string, and numbers (integer, real, rational and complex) can be translated.

Rus3(scheme)> #f
==> false
Rus3(scheme)> #t
==> true
Rus3(scheme)> ()
==> []
Rus3(scheme)> "foo"
==> "foo"
Rus3(scheme)> 123.456
==> 123.456
Rus3(scheme)> 1/9
==> (1/9)
Rus3(scheme)> 3+4i
==> (3+4i)
Rus3(scheme)> #(1 2 3)
==> #<Rus3::Vector:0x00007facf12d9fb0 @content=[1, 2, 3]>
Rus3(scheme)> #\a
==> #<Rus3::Char:0x00007fc41f1059d8
 @char="a",
 @codepoint=97,
 @encoding=#<Encoding:UTF-8>>

You can apply a defined procedure.

Rus3(scheme)> (list 1 2 3)
==> [1, 2, 3]
Rus3(scheme)> (append (list 1 2 3) (list 4 5 6))
==> [1, 2, 3, 4, 5, 6]

You can apply lambda expression as a procedure.

Rus3(scheme)> ((lambda (x) (* x x)) 2)
==> 4

Rus3(scheme)> (if (< 2 3) "true" "false")
==> "true"

cond type is also available.

Rus3(scheme)> (set! x 2)
==> 2
Rus3(scheme)> x
==> 2

Rus3(scheme)> (define (fact n) (if (= n 0) 1 (* n (fact (- n 1)))))
==> :fact
Rus3(scheme)> (fact 5)
==> 120

Rus3(scheme)> (let ((x 2) (y 3)) (* x y))
==> 6

Following procedures described in the spec is available.

• Predicates:

  • null?, list?
  • eqv?, eq?
  • boolean?, pair?, symbol?, number?, string?, vector?, char?
    • port? are defined but it always returns false.
  • complex?, real?, rational?, integer?
  • zero?, positive?, negative?, odd?, even?
  • string-eq?, string-ci-eq?, string-lt?, string-gt?, string-le?, string-ge?, string-ci-lt?, string-ci-gt?, string-ci-le?, string-ci-ge?
  • char-eq?, char-lt?, char-gt?, char-le?, char-ge?, char-ci-eq?, char-ci-lt?, char-ci-gt?, char-ci-le?, char-ci-ge?, char-alphabetic?, char-numeric?, char-whitespace?, char-upper-case?, char-lower-case?
  • some predicates for port are defined but it always returns false.

• List operations

  • cons, car, cdr, set-car!, set-cdr!, cxxr (caar and so on)
  • list, length, append, reverse, list-tail, list-ref

• Vector operations

  • make-vector, vector, vector-length, vector-ref, vector-set!, vector->list, list->vector, vector-fill!

• Char operations

  • char->integer, integer->char, char-upcase, char-downcase

• Write values

  • write
  • display

• Control features

  • map
  • zip

Reads a Scheme program file, then translates and evaluates.

Rus3(scheme)> (load-scm "examples/iota.scm")
(1 2 3 4 5 6 7 8 9 10)
(1/9 2/9 1/3 4/9 5/9 2/3 7/9 8/9 1/1 10/9)
==> #<Rus3::Undef:0x00007f90f8945418>

In the current version, there are several restrictions, those are deviations from the Scheme specification (R5RS or R7RS-small).

• Equal? does not defined. Since Object#equal? must not re-define in Ruby.
• Cdr and list-tail do not return a reference of the part of the target list. They return a new list structure which contains the same member of the target list.
• Rus3 would replace some character which can not use as a part of identifier in Ruby. So, it is possible that some collision of identifiers.
• Nested definition of procedure can use outside.
• All characters and strings are treated as encoded in UTF-8.

Some of these may be disappeared in the future version, or may not be.

After checking out the repo, run bin/setup to install dependencies. Then, run rake test to run the tests. You can also run bin/console for an interactive prompt that will allow you to experiment.

To install this gem onto your local machine, run bundle exec rake install. To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version, push git commits and tags, and push the .gem file to rubygems.org.

Bug reports and pull requests are welcome on GitHub at https://github.com/mnbi/rus3.

The gem is available as open source under the terms of the MIT License.