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iScheme based on the Metaobject protocol

From: Keisuke Nishida
Subject: iScheme based on the Metaobject protocol
Date: 07 Nov 2000 04:08:56 -0500
User-agent: T-gnus/6.14.4 (based on Gnus v5.8.6) (revision 02) SEMI/1.13.7 (Awazu) Chao/1.14.0 (Momoyama) Emacs/20.7 (i686-pc-linux-gnu) MULE/4.1 (AOI)


Because of the fun of it, I'm still thinking about iScheme.
I guess I'll make it completely based on the Metaobject protocol
(though I haven't understood it quite well yet).

Primitive @lambda creates a method:

  (@define add-integer
    (@lambda ((<integer> x) (<integer> y))
      (+ x y)))

  (add-integer 1 2)     => 3

Several methods can be combined into a generic function:

  (@define add-string
    (@lambda ((<string> x) (<string> y))
      (string-append x y)))

  (@define add (@make-generic add-integer add-string))

  (add 1 2)             => 3
  (add "a" "b")         => "ab"

A new method can be added easily:

  (@define (add (<list> x) (<list> y))
    (append x y))

  (add '(1) '(2))       => (1 2)

So, the following two expressions are different in iScheme:

  (@define (foo) 1)             ;; `foo' is a generic function
  (@define foo (@lambda () 1))  ;; `foo' is a method

The latter is more efficient when (foo) is evaluated.

Special notation <const> allows to define a method for a particular
object instead of class:

  (@define (add (<const> 'double) y)
    (add y y))

  (add 'double "ab")    => "abab"
  (add 'single "ab")    ;; ERROR

<const> can be omitted:

  (@define (add 'single y) y)

  (add 'single "ab")    => "ab"

Is this a good thing?  I guess this is feasible, though I'm not sure
how efficiently it could be implemented.

By using the notation above, the following Haskell-like code

  fact 0 = 1
  fact n = n * fact (n - 1)

might be translated into the following iScheme code:

  (@define (fact 0) 1)
  (@define (fact n) (* n (fact (- n 1))))

(I know this is not sufficient as a translation of Haskell yet.)

Thinking about this kind of stuff is really fun, after all :)
I guess I'll continue working on iScheme until I realize it is
a stupid thing...

This is the current draft:

Any comment is appreciated.

Keisuke Nishida

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