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    Length: 3065 (0xbf9)
    Types: TextFile
    Names: »strmac.scm.2«

└─⟦a0efdde77⟧ Bits:30001252 EUUGD11 Tape, 1987 Spring Conference Helsinki
    └─⟦this⟧ »EUUGD11/gnu-31mar87/scheme/scm/strmac.scm.2« 

TextFile

;;; -*-Scheme-*-
;;;
;;;	Copyright (c) 1984 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.
;;;

;;;; Stream Macros

(declare (usual-integrations))
\f


((access add-syntax! '())
 'CONS-STREAM
 (macro (head tail)
   `(CONS ,head (DELAY ,tail))))

((access add-syntax! '())
 'COLLECT
 (let ()
   (define (collect-macro-kernel result bindings filter)
     (if (null? bindings)
	 (error "No bindings -- COLLECT"))
     (parse-bindings bindings
       (lambda (names sets)
	 (define (make-tuple-generator names* sets)
	   (if (null? (cdr names*))
	       `(MAP (LAMBDA (,(car names*))
		       (LIST ,@names))
		     ,(car sets))
	       `(FLATMAP (LAMBDA (,(car names*))
			   ,(make-tuple-generator (cdr names*)
						  (cdr sets)))
			 ,(car sets))))

	 `(MAP (SPREAD-TUPLE (LAMBDA ,names ,result))
	       ,(let ((tuple-generator (make-tuple-generator names sets)))
		  (if (null? filter)
		      tuple-generator
		      `(FILTER (SPREAD-TUPLE (LAMBDA ,names ,@filter))
			       ,tuple-generator)))))))

   (define (parse-bindings bindings receiver)
     (if (null? bindings)
	 (receiver '() '())
	 (sequence
	  (if (not (pair? bindings))
	      (error "Bindings must be a list -- COLLECT" bindings))
	  (parse-bindings (cdr bindings)
	    (lambda (names sets)
	      (if (not (conjunction (list? (car bindings))
				    (= (length (car bindings)) 2)
				    (symbol? (caar bindings))))
		  (error "Badly formed binding -- COLLECT" (car bindings)))
	      (receiver (cons (caar bindings) names)
			(cons (cadar bindings) sets)))))))

   (macro (result bindings . filter)
     (collect-macro-kernel result bindings filter))))