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    Length: 3753 (0xea9)
    Types: TextFile
    Names: »sample.scm«, »sample.scm.1«

└─⟦a0efdde77⟧ Bits:30001252 EUUGD11 Tape, 1987 Spring Conference Helsinki
    └─⟦this⟧ »EUUGD11/gnu-31mar87/scheme/microcode/sample.scm« 
    └─⟦this⟧ »EUUGD11/gnu-31mar87/scheme/scm/sample.scm.1« 

TextFile

;;;	Shouldn't -*-Scheme-*- be the only language?
;;;
;;;	Copyright (c) 1986 Massachusetts Institute of Technology
;;;
;;;	This material was developed by the Scheme project at the
;;;	Massachusetts Institute of Technology, Department of
;;;	Electrical Engineering and Computer Science.  Permission to
;;;	copy this software, to redistribute it, and to use it for any
;;;	purpose is granted, subject to the following restrictions and
;;;	understandings.
;;;
;;;	1. Any copy made of this software must include this copyright
;;;	notice in full.
;;;
;;;	2. Users of this software agree to make their best efforts (a)
;;;	to return to the MIT Scheme project any improvements or
;;;	extensions that they make, so that these may be included in
;;;	future releases; and (b) to inform MIT of noteworthy uses of
;;;	this software.
;;;
;;;	3.  All materials developed as a consequence of the use of
;;;	this software shall duly acknowledge such use, in accordance
;;;	with the usual standards of acknowledging credit in academic
;;;	research.
;;;
;;;	4. MIT has made no warrantee or representation that the
;;;	operation of this software will be error-free, and MIT is
;;;	under no obligation to provide any services, by way of
;;;	maintenance, update, or otherwise.
;;;
;;;	5.  In conjunction with products arising from the use of this
;;;	material, there shall be no use of the name of the
;;;	Massachusetts Institute of Technology nor of any adaptation
;;;	thereof in any advertising, promotional, or sales literature
;;;	without prior written consent from MIT in each case.
\f


;;;     Documentation on how to access new primitives from scheme.
;;;     
;;;     Primitives are accessed by using the procedure
;;;     MAKE-PRIMITIVE-PROCEDURE.  This procedure expects a symbol,
;;;     the "linkage" name of the primitive object being requested,
;;;     and an optional second argument specifying the action to take
;;;     if the primitive does not exist.
;;;     
;;;     Thus 
;;;     (make-primitive-procedure 'foo)
;;;     will return the primitive procedure object for FOO if it
;;;     exists, or will give an error if it does not.  On the other hand, 
;;;     (make-primitive-procedure 'foo #!TRUE)
;;;     will return a primitive procedure object always.  If FOO is
;;;     implemented, it will return the appropriate object, but if it
;;;     is not it will return a placeholder for the real object.  This
;;;     placeholder will cause an error if invoked (applied).  After
;;;     all, the code for FOO is not known.  However, if it is dumped
;;;     (as part of some larger piece of code, for example), and
;;;     reloaded into a system which DOES have FOO implemented, it
;;;     will be a valid primitive object for FOO (will work when
;;;     invoked).
;;;     A further utility is IMPLEMENTED-PRIMITIVE-PROCEDURE?, which
;;;     given a primitive procedure object returns #!TRUE if it is
;;;     implemented in the current system, #!FALSE if it is not.  Note
;;;     that it will always return #!TRUE on "built in" primitives,
;;;     even if they are not truly implemented.  It is only really
;;;     useful with optional (external) primitives.

;;;     The following code defines variables to hold the primitives
;;;     defined in SAMPLE.C.  Note that they will always contain
;;;     primitive objects since MAKE-PRIMITIVE-PROCEDURE has benn
;;;     given #!true as the second optional argument.

(define return-nil
  (make-primitive-procedure 'return-nil #!TRUE))
(define identity
  (make-primitive-procedure 'identity #!TRUE))
(define new-cons
  (make-primitive-procedure 'new-cons #!TRUE))
(define list-3-arguments
  (make-primitive-procedure 'why-shouldnt-the-name-be-random? #!TRUE))
(define 3+
  (make-primitive-procedure '3+ #!TRUE))