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[Guile-commits] GNU Guile branch, master, updated. release_1-9-12-129-gf


From: Andy Wingo
Subject: [Guile-commits] GNU Guile branch, master, updated. release_1-9-12-129-gfdc8fd4
Date: Sun, 03 Oct 2010 10:08:44 +0000

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http://git.savannah.gnu.org/cgit/guile.git/commit/?id=fdc8fd46fd02d072b6b5f183178862650fe36305

The branch, master has been updated
       via  fdc8fd46fd02d072b6b5f183178862650fe36305 (commit)
      from  6e3d49a0731bca22d8c3b4151a5a7121802a97c1 (commit)

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- Log -----------------------------------------------------------------
commit fdc8fd46fd02d072b6b5f183178862650fe36305
Author: Andreas Rottmann <address@hidden>
Date:   Sun Oct 3 12:06:38 2010 +0200

    Add implementation of SRFI 42
    
    * module/srfi/srfi-42/ec.scm: New file; reference implementation of
      SRFI 42.
    * module/srfi/srfi-42.scm: New file; module for SRFI 42.
    * module/Makefile.am (SRFI_SOURCES): Add srfi/srfi-42.scm.
      (NOCOMP_SOURCES): Add srfi/srfi-42/ec.scm.
    
    * test-suite/tests/srfi-42.test: New file; test suite for SRFI 42.
    * test-suite/Makefile.am: SCM_TESTS: Add tests/srfi-42.test.

-----------------------------------------------------------------------

Summary of changes:
 NEWS                          |    7 +-
 doc/ref/srfi-modules.texi     |    7 +
 module/Makefile.am            |    2 +
 module/srfi/srfi-42.scm       |   64 +++
 module/srfi/srfi-42/ec.scm    | 1053 +++++++++++++++++++++++++++++++++++++++++
 test-suite/Makefile.am        |    1 +
 test-suite/tests/srfi-42.test |  618 ++++++++++++++++++++++++
 7 files changed, 1750 insertions(+), 2 deletions(-)
 create mode 100644 module/srfi/srfi-42.scm
 create mode 100644 module/srfi/srfi-42/ec.scm
 create mode 100644 test-suite/tests/srfi-42.test

diff --git a/NEWS b/NEWS
index 0449b1d..5e9fd03 100644
--- a/NEWS
+++ b/NEWS
@@ -11,9 +11,12 @@ latest prerelease, and a full NEWS corresponding to 1.8 -> 
2.0.
 
 Changes in 1.9.12 (since the 1.9.11 prerelease):
 
-** Support for SRFI-27
+** SRFI support
 
-SRFI-27 "Sources of Random Bits" is now available.
+The following SRFIs have been added:
+
+- SRFI-27 "Sources of Random Bits"
+- SRFI-42 "Eager Comprehensions"
 
 ** Many R6RS bugfixes
 
diff --git a/doc/ref/srfi-modules.texi b/doc/ref/srfi-modules.texi
index 8a0b014..780f10d 100644
--- a/doc/ref/srfi-modules.texi
+++ b/doc/ref/srfi-modules.texi
@@ -43,6 +43,7 @@ get the relevant SRFI documents from the SRFI home page
 * SRFI-35::                     Conditions.
 * SRFI-37::                     args-fold program argument processor
 * SRFI-39::                     Parameter objects
+* SRFI-42::                     Eager comprehensions
 * SRFI-55::                     Requiring Features.
 * SRFI-60::                     Integers as bits.
 * SRFI-61::                     A more general `cond' clause
@@ -3866,6 +3867,12 @@ SRFI-39 doesn't specify the interaction between 
parameter objects and
 threads, so the threading behaviour described here should be regarded
 as Guile-specific.
 
address@hidden SRFI-42
address@hidden SRFI-42 - Eager Comprehensions
address@hidden SRFI-42
+
+See @uref{http://srfi.schemers.org/srfi-42/srfi-42.html, the
+specification of SRFI-42}.
 
 @node SRFI-55
 @subsection SRFI-55 - Requiring Features
diff --git a/module/Makefile.am b/module/Makefile.am
index 4ab649b..6197a43 100644
--- a/module/Makefile.am
+++ b/module/Makefile.am
@@ -253,6 +253,7 @@ SRFI_SOURCES = \
   srfi/srfi-34.scm \
   srfi/srfi-35.scm \
   srfi/srfi-37.scm \
+  srfi/srfi-42.scm \
   srfi/srfi-39.scm \
   srfi/srfi-60.scm \
   srfi/srfi-69.scm \
@@ -349,6 +350,7 @@ NOCOMP_SOURCES =                            \
   ice-9/psyntax.scm                            \
   ice-9/r6rs-libraries.scm                     \
   ice-9/quasisyntax.scm                                \
+  srfi/srfi-42/ec.scm                          \
   system/base/lalr.upstream.scm                        \
   system/repl/describe.scm                     \
   sxml/sxml-match.ss                           \
diff --git a/module/srfi/srfi-42.scm b/module/srfi/srfi-42.scm
new file mode 100644
index 0000000..0aaaf8f
--- /dev/null
+++ b/module/srfi/srfi-42.scm
@@ -0,0 +1,64 @@
+;;; srfi-42.scm --- Eager comprehensions
+
+;; Copyright (C) 2010 Free Software Foundation, Inc.
+
+;; This library is free software; you can redistribute it and/or
+;; modify it under the terms of the GNU Lesser General Public
+;; License as published by the Free Software Foundation; either
+;; version 3 of the License, or (at your option) any later version.
+
+;; This library is distributed in the hope that it will be useful,
+;; but WITHOUT ANY WARRANTY; without even the implied warranty of
+;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+;; Lesser General Public License for more details.
+
+;; You should have received a copy of the GNU Lesser General Public
+;; License along with this library. If not, see
+;; <http://www.gnu.org/licenses/>.
+
+;;; Commentary:
+
+;; This module is not yet documented in the Guile Reference Manual.
+
+;;; Code:
+
+(define-module (srfi srfi-42)
+  #:export (:
+            :-dispatch-ref
+            :-dispatch-set!
+            :char-range
+            :dispatched
+            :do
+            :generator-proc
+            :integers
+            :let
+            :list
+            :parallel
+            :port
+            :range
+            :real-range
+            :string
+            :until
+            :vector
+            :while
+            any?-ec
+            append-ec
+            dispatch-union
+            do-ec
+            every?-ec
+            first-ec
+            fold-ec
+            fold3-ec
+            last-ec
+            list-ec
+            make-initial-:-dispatch
+            max-ec
+            min-ec
+            product-ec
+            string-append-ec
+            string-ec
+            sum-ec
+            vector-ec
+            vector-of-length-ec))
+
+(include-from-path "srfi/srfi-42/ec.scm")
diff --git a/module/srfi/srfi-42/ec.scm b/module/srfi/srfi-42/ec.scm
new file mode 100644
index 0000000..bc0616e
--- /dev/null
+++ b/module/srfi/srfi-42/ec.scm
@@ -0,0 +1,1053 @@
+; <PLAINTEXT>
+; Eager Comprehensions in [outer..inner|expr]-Convention
+; ======================================================
+;
+; address@hidden, Eindhoven, The Netherlands, 26-Dec-2007
+; Scheme R5RS (incl. macros), SRFI-23 (error).
+; 
+; Loading the implementation into Scheme48 0.57:
+;   ,open srfi-23
+;   ,load ec.scm
+;
+; Loading the implementation into PLT/DrScheme 317:
+;   ; File > Open ... "ec.scm", click Execute
+;
+; Loading the implementation into SCM 5d7:
+;   (require 'macro) (require 'record) 
+;   (load "ec.scm")
+;
+; Implementation comments:
+;   * All local (not exported) identifiers are named ec-<something>.
+;   * This implementation focuses on portability, performance, 
+;     readability, and simplicity roughly in this order. Design
+;     decisions related to performance are taken for Scheme48.
+;   * Alternative implementations, Comments and Warnings are 
+;     mentioned after the definition with a heading.
+
+
+; ==========================================================================
+; The fundamental comprehension do-ec
+; ==========================================================================
+;
+; All eager comprehensions are reduced into do-ec and
+; all generators are reduced to :do. 
+;
+; We use the following short names for syntactic variables
+;   q    - qualifier
+;   cc   - current continuation, thing to call at the end;
+;          the CPS is (m (cc ...) arg ...) -> (cc ... expr ...)
+;   cmd  - an expression being evaluated for its side-effects
+;   expr - an expression
+;   gen  - a generator of an eager comprehension
+;   ob   - outer binding
+;   oc   - outer command
+;   lb   - loop binding
+;   ne1? - not-end1? (before the payload)
+;   ib   - inner binding
+;   ic   - inner command
+;   ne2? - not-end2? (after the payload)
+;   ls   - loop step
+;   etc  - more arguments of mixed type
+
+
+; (do-ec q ... cmd)
+;   handles nested, if/not/and/or, begin, :let, and calls generator 
+;   macros in CPS to transform them into fully decorated :do.
+;   The code generation for a :do is delegated to do-ec:do.
+
+(define-syntax do-ec
+  (syntax-rules (nested if not and or begin :do let)
+
+    ; explicit nesting -> implicit nesting
+    ((do-ec (nested q ...) etc ...)
+     (do-ec q ... etc ...) )
+
+    ; implicit nesting -> fold do-ec
+    ((do-ec q1 q2 etc1 etc ...)
+     (do-ec q1 (do-ec q2 etc1 etc ...)) )
+
+    ; no qualifiers at all -> evaluate cmd once
+    ((do-ec cmd)
+     (begin cmd (if #f #f)) )
+
+; now (do-ec q cmd) remains
+
+    ; filter -> make conditional
+    ((do-ec (if test) cmd)
+     (if test (do-ec cmd)) )
+    ((do-ec (not test) cmd)
+     (if (not test) (do-ec cmd)) )
+    ((do-ec (and test ...) cmd)
+     (if (and test ...) (do-ec cmd)) )
+    ((do-ec (or test ...) cmd)
+     (if (or test ...) (do-ec cmd)) )
+
+    ; begin -> make a sequence
+    ((do-ec (begin etc ...) cmd)
+     (begin etc ... (do-ec cmd)) )
+
+    ; fully decorated :do-generator -> delegate to do-ec:do
+    ((do-ec (:do olet lbs ne1? ilet ne2? lss) cmd)
+     (do-ec:do cmd (:do olet lbs ne1? ilet ne2? lss)) )
+
+; anything else -> call generator-macro in CPS; reentry at (*)
+
+    ((do-ec (g arg1 arg ...) cmd)
+     (g (do-ec:do cmd) arg1 arg ...) )))
+
+
+; (do-ec:do cmd (:do olet lbs ne1? ilet ne2? lss))
+;   generates code for a single fully decorated :do-generator
+;   with cmd as payload, taking care of special cases.
+
+(define-syntax do-ec:do
+  (syntax-rules (:do let)
+
+    ; reentry point (*) -> generate code
+    ((do-ec:do cmd 
+               (:do (let obs oc ...) 
+                    lbs 
+                    ne1? 
+                    (let ibs ic ...) 
+                    ne2? 
+                    (ls ...) ))
+     (ec-simplify
+       (let obs
+         oc ...
+         (let loop lbs
+           (ec-simplify
+             (if ne1?
+                 (ec-simplify
+                   (let ibs
+                      ic ...
+                      cmd
+                      (ec-simplify
+                        (if ne2?
+                            (loop ls ...) )))))))))) ))
+
+    
+; (ec-simplify <expression>)
+;   generates potentially more efficient code for <expression>.
+;   The macro handles if, (begin <command>*), and (let () <command>*)
+;   and takes care of special cases.
+
+(define-syntax ec-simplify
+  (syntax-rules (if not let begin)
+
+; one- and two-sided if
+
+    ; literal <test>
+    ((ec-simplify (if #t consequent))
+     consequent )
+    ((ec-simplify (if #f consequent))
+     (if #f #f) )
+    ((ec-simplify (if #t consequent alternate))
+     consequent )
+    ((ec-simplify (if #f consequent alternate))
+     alternate )
+
+    ; (not (not <test>))
+    ((ec-simplify (if (not (not test)) consequent))
+     (ec-simplify (if test consequent)) )
+    ((ec-simplify (if (not (not test)) consequent alternate))
+     (ec-simplify (if test consequent alternate)) )
+
+; (let () <command>*) 
+
+    ; empty <binding spec>*
+    ((ec-simplify (let () command ...))
+     (ec-simplify (begin command ...)) )
+
+; begin 
+
+    ; flatten use helper (ec-simplify 1 done to-do)
+    ((ec-simplify (begin command ...))
+     (ec-simplify 1 () (command ...)) )
+    ((ec-simplify 1 done ((begin to-do1 ...) to-do2 ...))
+     (ec-simplify 1 done (to-do1 ... to-do2 ...)) )
+    ((ec-simplify 1 (done ...) (to-do1 to-do ...))
+     (ec-simplify 1 (done ... to-do1) (to-do ...)) )
+
+    ; exit helper
+    ((ec-simplify 1 () ())
+     (if #f #f) )
+    ((ec-simplify 1 (command) ())
+     command )
+    ((ec-simplify 1 (command1 command ...) ())
+     (begin command1 command ...) )
+
+; anything else
+
+    ((ec-simplify expression)
+     expression )))
+
+
+; ==========================================================================
+; The special generators :do, :let, :parallel, :while, and :until
+; ==========================================================================
+
+(define-syntax :do
+  (syntax-rules ()
+
+    ; full decorated -> continue with cc, reentry at (*)
+    ((:do (cc ...) olet lbs ne1? ilet ne2? lss)
+     (cc ... (:do olet lbs ne1? ilet ne2? lss)) )
+
+    ; short form -> fill in default values
+    ((:do cc lbs ne1? lss)
+     (:do cc (let ()) lbs ne1? (let ()) #t lss) )))
+    
+
+(define-syntax :let
+  (syntax-rules (index)
+    ((:let cc var (index i) expression)
+     (:do cc (let ((var expression) (i 0))) () #t (let ()) #f ()) )
+    ((:let cc var expression)
+     (:do cc (let ((var expression))) () #t (let ()) #f ()) )))
+
+
+(define-syntax :parallel
+  (syntax-rules (:do)
+    ((:parallel cc)
+     cc )
+    ((:parallel cc (g arg1 arg ...) gen ...)
+     (g (:parallel-1 cc (gen ...)) arg1 arg ...) )))
+
+; (:parallel-1 cc (to-do ...) result [ next ] )
+;    iterates over to-do by converting the first generator into 
+;    the :do-generator next and merging next into result.
+
+(define-syntax :parallel-1  ; used as 
+  (syntax-rules (:do let)
+
+    ; process next element of to-do, reentry at (**)
+    ((:parallel-1 cc ((g arg1 arg ...) gen ...) result)
+     (g (:parallel-1 cc (gen ...) result) arg1 arg ...) )
+
+    ; reentry point (**) -> merge next into result
+    ((:parallel-1 
+       cc 
+       gens 
+       (:do (let (ob1 ...) oc1 ...) 
+            (lb1 ...) 
+            ne1?1 
+            (let (ib1 ...) ic1 ...) 
+            ne2?1 
+            (ls1 ...) )
+       (:do (let (ob2 ...) oc2 ...) 
+            (lb2 ...) 
+            ne1?2 
+            (let (ib2 ...) ic2 ...) 
+            ne2?2 
+            (ls2 ...) ))
+     (:parallel-1 
+       cc 
+       gens 
+       (:do (let (ob1 ... ob2 ...) oc1 ... oc2 ...) 
+            (lb1 ... lb2 ...) 
+            (and ne1?1 ne1?2) 
+            (let (ib1 ... ib2 ...) ic1 ... ic2 ...) 
+            (and ne2?1 ne2?2) 
+            (ls1 ... ls2 ...) )))
+
+    ; no more gens -> continue with cc, reentry at (*)
+    ((:parallel-1 (cc ...) () result)
+     (cc ... result) )))
+
+(define-syntax :while
+  (syntax-rules ()
+    ((:while cc (g arg1 arg ...) test)
+     (g (:while-1 cc test) arg1 arg ...) )))
+
+; (:while-1 cc test (:do ...))
+;    modifies the fully decorated :do-generator such that it
+;    runs while test is a true value. 
+;       The original implementation just replaced ne1? by
+;    (and ne1? test) as follows:
+;
+;      (define-syntax :while-1
+;        (syntax-rules (:do)
+;          ((:while-1 cc test (:do olet lbs ne1? ilet ne2? lss))
+;           (:do cc olet lbs (and ne1? test) ilet ne2? lss) )))
+;
+; Bug #1:
+;    Unfortunately, this code is wrong because ne1? may depend
+;    in the inner bindings introduced in ilet, but ne1? is evaluated
+;    outside of the inner bindings. (Refer to the specification of
+;    :do to see the structure.) 
+;       The problem manifests itself (as address@hidden 
+;    observed, 25-Apr-2005) when the :list-generator is modified:
+; 
+;      (do-ec (:while (:list x '(1 2)) (= x 1)) (display x)).
+;
+;    In order to generate proper code, we introduce temporary
+;    variables saving the values of the inner bindings. The inner
+;    bindings are executed in a new ne1?, which also evaluates ne1?
+;    outside the scope of the inner bindings, then the inner commands
+;    are executed (possibly changing the variables), and then the
+;    values of the inner bindings are saved and (and ne1? test) is
+;    returned. In the new ilet, the inner variables are bound and
+;    initialized and their values are restored. So we construct:
+;
+;     (let (ob .. (ib-tmp #f) ...)
+;       oc ...
+;       (let loop (lb ...)
+;         (if (let (ne1?-value ne1?)
+;               (let ((ib-var ib-rhs) ...)
+;                 ic ...
+;                 (set! ib-tmp ib-var) ...)
+;               (and ne1?-value test))
+;             (let ((ib-var ib-tmp) ...)
+;               /payload/
+;               (if ne2?
+;                   (loop ls ...) )))))
+; 
+; Bug #2:
+;    Unfortunately, the above expansion is still incorrect (as Jens-Axel 
+;    Soegaard pointed out, 4-Jun-2007) because ib-rhs are evaluated even
+;    if ne1?-value is #f, indicating that the loop has ended.
+;       The problem manifests itself in the following example:
+;
+;      (do-ec (:while (:list x '(1)) #t) (display x))
+;
+;    Which iterates :list beyond exhausting the list '(1).
+;
+;    For the fix, we follow Jens-Axel's approach of guarding the evaluation
+;    of ib-rhs with a check on ne1?-value.
+
+(define-syntax :while-1
+  (syntax-rules (:do let)
+    ((:while-1 cc test (:do olet lbs ne1? ilet ne2? lss))
+     (:while-2 cc test () () () (:do olet lbs ne1? ilet ne2? lss)))))
+
+(define-syntax :while-2
+  (syntax-rules (:do let)
+    ((:while-2 cc 
+               test 
+               (ib-let     ...)
+               (ib-save    ...)
+               (ib-restore ...)
+               (:do olet 
+                    lbs 
+                    ne1? 
+                    (let ((ib-var ib-rhs) ib ...) ic ...)
+                    ne2? 
+                    lss))
+     (:while-2 cc 
+               test 
+               (ib-let     ... (ib-tmp #f))
+               (ib-save    ... (ib-var ib-rhs))
+               (ib-restore ... (ib-var ib-tmp))
+               (:do olet 
+                    lbs 
+                    ne1? 
+                    (let (ib ...) ic ... (set! ib-tmp ib-var)) 
+                    ne2? 
+                    lss)))
+    ((:while-2 cc
+               test
+               (ib-let     ...)
+               (ib-save    ...)
+               (ib-restore ...)
+               (:do (let (ob ...) oc ...) lbs ne1? (let () ic ...) ne2? lss))
+     (:do cc
+          (let (ob ... ib-let ...) oc ...)
+          lbs
+          (let ((ne1?-value ne1?))
+           (and ne1?-value
+                (let (ib-save ...)
+                  ic ...
+                  test)))
+          (let (ib-restore ...))
+          ne2?
+          lss))))
+
+
+(define-syntax :until
+  (syntax-rules ()
+    ((:until cc (g arg1 arg ...) test)
+     (g (:until-1 cc test) arg1 arg ...) )))
+
+(define-syntax :until-1
+  (syntax-rules (:do)
+    ((:until-1 cc test (:do olet lbs ne1? ilet ne2? lss))
+     (:do cc olet lbs ne1? ilet (and ne2? (not test)) lss) )))
+
+
+; ==========================================================================
+; The typed generators :list :string :vector etc.
+; ==========================================================================
+
+(define-syntax :list
+  (syntax-rules (index)
+    ((:list cc var (index i) arg ...)
+     (:parallel cc (:list var arg ...) (:integers i)) )
+    ((:list cc var arg1 arg2 arg ...)
+     (:list cc var (append arg1 arg2 arg ...)) )
+    ((:list cc var arg)
+     (:do cc
+          (let ())
+          ((t arg))
+          (not (null? t))
+          (let ((var (car t))))
+          #t
+          ((cdr t)) ))))
+
+
+(define-syntax :string
+  (syntax-rules (index)
+    ((:string cc var (index i) arg)
+     (:do cc
+          (let ((str arg) (len 0)) 
+            (set! len (string-length str)))
+          ((i 0))
+          (< i len)
+          (let ((var (string-ref str i))))
+          #t
+          ((+ i 1)) ))
+    ((:string cc var (index i) arg1 arg2 arg ...)
+     (:string cc var (index i) (string-append arg1 arg2 arg ...)) )
+    ((:string cc var arg1 arg ...)
+     (:string cc var (index i) arg1 arg ...) )))
+
+; Alternative: An implementation in the style of :vector can also
+;   be used for :string. However, it is less interesting as the
+;   overhead of string-append is much less than for 'vector-append'.
+
+
+(define-syntax :vector
+  (syntax-rules (index)
+    ((:vector cc var arg)
+     (:vector cc var (index i) arg) )
+    ((:vector cc var (index i) arg)
+     (:do cc
+          (let ((vec arg) (len 0)) 
+            (set! len (vector-length vec)))
+          ((i 0))
+          (< i len)
+          (let ((var (vector-ref vec i))))
+          #t
+          ((+ i 1)) ))
+
+    ((:vector cc var (index i) arg1 arg2 arg ...)
+     (:parallel cc (:vector cc var arg1 arg2 arg ...) (:integers i)) )
+    ((:vector cc var arg1 arg2 arg ...)
+     (:do cc
+          (let ((vec #f)
+                (len 0)
+                (vecs (ec-:vector-filter (list arg1 arg2 arg ...))) ))
+          ((k 0))
+          (if (< k len)
+              #t
+              (if (null? vecs)
+                  #f
+                  (begin (set! vec (car vecs))
+                         (set! vecs (cdr vecs))
+                         (set! len (vector-length vec))
+                         (set! k 0)
+                         #t )))
+          (let ((var (vector-ref vec k))))
+          #t
+          ((+ k 1)) ))))
+
+(define (ec-:vector-filter vecs)
+  (if (null? vecs)
+      '()
+      (if (zero? (vector-length (car vecs)))
+          (ec-:vector-filter (cdr vecs))
+          (cons (car vecs) (ec-:vector-filter (cdr vecs))) )))
+
+; Alternative: A simpler implementation for :vector uses vector->list
+;   append and :list in the multi-argument case. Please refer to the
+;   'design.scm' for more details.
+
+
+(define-syntax :integers
+  (syntax-rules (index)
+    ((:integers cc var (index i))
+     (:do cc ((var 0) (i 0)) #t ((+ var 1) (+ i 1))) )
+    ((:integers cc var)
+     (:do cc ((var 0)) #t ((+ var 1))) )))
+
+
+(define-syntax :range
+  (syntax-rules (index)
+
+    ; handle index variable and add optional args
+    ((:range cc var (index i) arg1 arg ...)
+     (:parallel cc (:range var arg1 arg ...) (:integers i)) )
+    ((:range cc var arg1)
+     (:range cc var 0 arg1 1) )
+    ((:range cc var arg1 arg2)
+     (:range cc var arg1 arg2 1) )
+
+; special cases (partially evaluated by hand from general case)
+
+    ((:range cc var 0 arg2 1)
+     (:do cc
+          (let ((b arg2))
+            (if (not (and (integer? b) (exact? b)))
+                (error 
+                   "arguments of :range are not exact integer "
+                   "(use :real-range?)" 0 b 1 )))
+          ((var 0))
+          (< var b)
+          (let ())
+          #t
+          ((+ var 1)) ))
+
+    ((:range cc var 0 arg2 -1)
+     (:do cc
+          (let ((b arg2))
+            (if (not (and (integer? b) (exact? b)))
+                (error 
+                   "arguments of :range are not exact integer "
+                   "(use :real-range?)" 0 b 1 )))
+          ((var 0))
+          (> var b)
+          (let ())
+          #t
+          ((- var 1)) ))
+
+    ((:range cc var arg1 arg2 1)
+     (:do cc
+          (let ((a arg1) (b arg2))
+            (if (not (and (integer? a) (exact? a)
+                          (integer? b) (exact? b) ))
+                (error 
+                   "arguments of :range are not exact integer "
+                   "(use :real-range?)" a b 1 )) )
+          ((var a))
+          (< var b)
+          (let ())
+          #t
+          ((+ var 1)) ))
+
+    ((:range cc var arg1 arg2 -1)
+     (:do cc
+          (let ((a arg1) (b arg2) (s -1) (stop 0))
+            (if (not (and (integer? a) (exact? a)
+                          (integer? b) (exact? b) ))
+                (error 
+                   "arguments of :range are not exact integer "
+                   "(use :real-range?)" a b -1 )) )
+          ((var a))
+          (> var b)
+          (let ())
+          #t
+          ((- var 1)) ))
+
+; the general case
+
+    ((:range cc var arg1 arg2 arg3)
+     (:do cc
+          (let ((a arg1) (b arg2) (s arg3) (stop 0))
+            (if (not (and (integer? a) (exact? a)
+                          (integer? b) (exact? b)
+                          (integer? s) (exact? s) ))
+                (error 
+                   "arguments of :range are not exact integer "
+                   "(use :real-range?)" a b s ))
+            (if (zero? s)
+                (error "step size must not be zero in :range") )
+            (set! stop (+ a (* (max 0 (ceiling (/ (- b a) s))) s))) )
+          ((var a))
+          (not (= var stop))
+          (let ())
+          #t
+          ((+ var s)) ))))
+
+; Comment: The macro :range inserts some code to make sure the values
+;   are exact integers. This overhead has proven very helpful for 
+;   saving users from themselves.
+
+
+(define-syntax :real-range
+  (syntax-rules (index)
+
+    ; add optional args and index variable
+    ((:real-range cc var arg1)
+     (:real-range cc var (index i) 0 arg1 1) )
+    ((:real-range cc var (index i) arg1)
+     (:real-range cc var (index i) 0 arg1 1) )
+    ((:real-range cc var arg1 arg2)
+     (:real-range cc var (index i) arg1 arg2 1) )
+    ((:real-range cc var (index i) arg1 arg2)
+     (:real-range cc var (index i) arg1 arg2 1) )
+    ((:real-range cc var arg1 arg2 arg3)
+     (:real-range cc var (index i) arg1 arg2 arg3) )
+
+    ; the fully qualified case
+    ((:real-range cc var (index i) arg1 arg2 arg3)
+     (:do cc
+          (let ((a arg1) (b arg2) (s arg3) (istop 0))
+            (if (not (and (real? a) (real? b) (real? s)))
+                (error "arguments of :real-range are not real" a b s) )
+            (if (and (exact? a) (or (not (exact? b)) (not (exact? s))))
+                (set! a (exact->inexact a)) )
+            (set! istop (/ (- b a) s)) )
+          ((i 0))
+          (< i istop)
+          (let ((var (+ a (* s i)))))
+          #t
+          ((+ i 1)) ))))
+
+; Comment: The macro :real-range adapts the exactness of the start
+;   value in case any of the other values is inexact. This is a
+;   precaution to avoid (list-ec (: x 0 3.0) x) => '(0 1.0 2.0).
+
+    
+(define-syntax :char-range
+  (syntax-rules (index)
+    ((:char-range cc var (index i) arg1 arg2)
+     (:parallel cc (:char-range var arg1 arg2) (:integers i)) )
+    ((:char-range cc var arg1 arg2)
+     (:do cc
+          (let ((imax (char->integer arg2))))
+          ((i (char->integer arg1)))
+          (<= i imax)
+          (let ((var (integer->char i))))
+          #t
+          ((+ i 1)) ))))
+
+; Warning: There is no R5RS-way to implement the :char-range generator 
+;   because the integers obtained by char->integer are not necessarily 
+;   consecutive. We simply assume this anyhow for illustration.
+
+
+(define-syntax :port
+  (syntax-rules (index)
+    ((:port cc var (index i) arg1 arg ...)
+     (:parallel cc (:port var arg1 arg ...) (:integers i)) )
+    ((:port cc var arg)
+     (:port cc var arg read) )
+    ((:port cc var arg1 arg2)
+     (:do cc
+          (let ((port arg1) (read-proc arg2)))
+          ((var (read-proc port)))
+          (not (eof-object? var))
+          (let ())
+          #t
+          ((read-proc port)) ))))
+
+
+; ==========================================================================
+; The typed generator :dispatched and utilities for constructing dispatchers
+; ==========================================================================
+
+(define-syntax :dispatched
+  (syntax-rules (index)
+    ((:dispatched cc var (index i) dispatch arg1 arg ...)
+     (:parallel cc 
+                (:integers i)
+                (:dispatched var dispatch arg1 arg ...) ))
+    ((:dispatched cc var dispatch arg1 arg ...)
+     (:do cc
+          (let ((d dispatch) 
+                (args (list arg1 arg ...)) 
+                (g #f) 
+                (empty (list #f)) )
+            (set! g (d args))
+            (if (not (procedure? g))
+                (error "unrecognized arguments in dispatching" 
+                       args 
+                       (d '()) )))
+          ((var (g empty)))
+          (not (eq? var empty))
+          (let ())
+          #t
+          ((g empty)) ))))
+
+; Comment: The unique object empty is created as a newly allocated
+;   non-empty list. It is compared using eq? which distinguishes
+;   the object from any other object, according to R5RS 6.1.
+
+
+(define-syntax :generator-proc
+  (syntax-rules (:do let)
+
+    ; call g with a variable, reentry at (**)
+    ((:generator-proc (g arg ...))
+     (g (:generator-proc var) var arg ...) )
+
+    ; reentry point (**) -> make the code from a single :do
+    ((:generator-proc
+       var 
+       (:do (let obs oc ...) 
+            ((lv li) ...) 
+            ne1? 
+            (let ((i v) ...) ic ...) 
+            ne2? 
+            (ls ...)) )
+     (ec-simplify 
+      (let obs
+          oc ...
+          (let ((lv li) ... (ne2 #t))
+            (ec-simplify
+             (let ((i #f) ...) ; v not yet valid
+               (lambda (empty)
+                 (if (and ne1? ne2)
+                     (ec-simplify
+                      (begin 
+                        (set! i v) ...
+                        ic ...
+                        (let ((value var))
+                          (ec-simplify
+                           (if ne2?
+                               (ec-simplify 
+                                (begin (set! lv ls) ...) )
+                               (set! ne2 #f) ))
+                          value )))
+                     empty ))))))))
+
+    ; silence warnings of some macro expanders
+    ((:generator-proc var)
+     (error "illegal macro call") )))
+
+
+(define (dispatch-union d1 d2)
+  (lambda (args)
+    (let ((g1 (d1 args)) (g2 (d2 args)))
+      (if g1
+          (if g2 
+              (if (null? args)
+                  (append (if (list? g1) g1 (list g1)) 
+                          (if (list? g2) g2 (list g2)) )
+                  (error "dispatching conflict" args (d1 '()) (d2 '())) )
+              g1 )
+          (if g2 g2 #f) ))))
+
+
+; ==========================================================================
+; The dispatching generator :
+; ==========================================================================
+
+(define (make-initial-:-dispatch)
+  (lambda (args)
+    (case (length args)
+      ((0) 'SRFI42)
+      ((1) (let ((a1 (car args)))
+             (cond
+              ((list? a1)
+               (:generator-proc (:list a1)) )
+              ((string? a1)
+               (:generator-proc (:string a1)) )
+              ((vector? a1)
+               (:generator-proc (:vector a1)) )
+              ((and (integer? a1) (exact? a1))
+               (:generator-proc (:range a1)) )
+              ((real? a1)
+               (:generator-proc (:real-range a1)) )
+              ((input-port? a1)
+               (:generator-proc (:port a1)) )
+              (else
+               #f ))))
+      ((2) (let ((a1 (car args)) (a2 (cadr args)))
+             (cond
+              ((and (list? a1) (list? a2))
+               (:generator-proc (:list a1 a2)) )
+              ((and (string? a1) (string? a1))
+               (:generator-proc (:string a1 a2)) )
+              ((and (vector? a1) (vector? a2))
+               (:generator-proc (:vector a1 a2)) )
+              ((and (integer? a1) (exact? a1) (integer? a2) (exact? a2))
+               (:generator-proc (:range a1 a2)) )
+              ((and (real? a1) (real? a2))
+               (:generator-proc (:real-range a1 a2)) )
+              ((and (char? a1) (char? a2))
+               (:generator-proc (:char-range a1 a2)) )
+              ((and (input-port? a1) (procedure? a2))
+               (:generator-proc (:port a1 a2)) )
+              (else
+               #f ))))
+      ((3) (let ((a1 (car args)) (a2 (cadr args)) (a3 (caddr args)))
+             (cond
+              ((and (list? a1) (list? a2) (list? a3))
+               (:generator-proc (:list a1 a2 a3)) )
+              ((and (string? a1) (string? a1) (string? a3))
+               (:generator-proc (:string a1 a2 a3)) )
+              ((and (vector? a1) (vector? a2) (vector? a3))
+               (:generator-proc (:vector a1 a2 a3)) )
+              ((and (integer? a1) (exact? a1) 
+                    (integer? a2) (exact? a2)
+                    (integer? a3) (exact? a3))
+               (:generator-proc (:range a1 a2 a3)) )
+              ((and (real? a1) (real? a2) (real? a3))
+               (:generator-proc (:real-range a1 a2 a3)) )
+              (else
+               #f ))))
+      (else
+       (letrec ((every? 
+                 (lambda (pred args)
+                   (if (null? args)
+                       #t
+                       (and (pred (car args))
+                            (every? pred (cdr args)) )))))
+         (cond
+          ((every? list? args)
+           (:generator-proc (:list (apply append args))) )
+          ((every? string? args)
+           (:generator-proc (:string (apply string-append args))) )
+          ((every? vector? args)
+           (:generator-proc (:list (apply append (map vector->list args)))) )
+          (else
+           #f )))))))
+
+(define :-dispatch
+  (make-initial-:-dispatch) )
+
+(define (:-dispatch-ref)
+  :-dispatch )
+
+(define (:-dispatch-set! dispatch)
+  (if (not (procedure? dispatch))
+      (error "not a procedure" dispatch) )
+  (set! :-dispatch dispatch) )
+
+(define-syntax :
+  (syntax-rules (index)
+    ((: cc var (index i) arg1 arg ...)
+     (:dispatched cc var (index i) :-dispatch arg1 arg ...) )
+    ((: cc var arg1 arg ...)
+     (:dispatched cc var :-dispatch arg1 arg ...) )))
+
+
+; ==========================================================================
+; The utility comprehensions fold-ec, fold3-ec
+; ==========================================================================
+
+(define-syntax fold3-ec
+  (syntax-rules (nested)
+    ((fold3-ec x0 (nested q1 ...) q etc1 etc2 etc3 etc ...)
+     (fold3-ec x0 (nested q1 ... q) etc1 etc2 etc3 etc ...) )
+    ((fold3-ec x0 q1 q2 etc1 etc2 etc3 etc ...)
+     (fold3-ec x0 (nested q1 q2) etc1 etc2 etc3 etc ...) )
+    ((fold3-ec x0 expression f1 f2)
+     (fold3-ec x0 (nested) expression f1 f2) )
+
+    ((fold3-ec x0 qualifier expression f1 f2)
+     (let ((result #f) (empty #t))
+       (do-ec qualifier
+              (let ((value expression)) ; don't duplicate
+                (if empty
+                    (begin (set! result (f1 value))
+                           (set! empty #f) )
+                    (set! result (f2 value result)) )))
+       (if empty x0 result) ))))
+
+
+(define-syntax fold-ec
+  (syntax-rules (nested)
+    ((fold-ec x0 (nested q1 ...) q etc1 etc2 etc ...)
+     (fold-ec x0 (nested q1 ... q) etc1 etc2 etc ...) )
+    ((fold-ec x0 q1 q2 etc1 etc2 etc ...)
+     (fold-ec x0 (nested q1 q2) etc1 etc2 etc ...) )
+    ((fold-ec x0 expression f2)
+     (fold-ec x0 (nested) expression f2) )
+
+    ((fold-ec x0 qualifier expression f2)
+     (let ((result x0))
+       (do-ec qualifier (set! result (f2 expression result)))
+       result ))))
+
+
+; ==========================================================================
+; The comprehensions list-ec string-ec vector-ec etc.
+; ==========================================================================
+
+(define-syntax list-ec
+  (syntax-rules ()
+    ((list-ec etc1 etc ...)
+     (reverse (fold-ec '() etc1 etc ... cons)) )))
+
+; Alternative: Reverse can safely be replaced by reverse! if you have it.
+;
+; Alternative: It is possible to construct the result in the correct order
+;   using set-cdr! to add at the tail. This removes the overhead of copying
+;   at the end, at the cost of more book-keeping.
+
+
+(define-syntax append-ec
+  (syntax-rules ()
+    ((append-ec etc1 etc ...)
+     (apply append (list-ec etc1 etc ...)) )))
+
+(define-syntax string-ec
+  (syntax-rules ()
+    ((string-ec etc1 etc ...)
+     (list->string (list-ec etc1 etc ...)) )))
+
+; Alternative: For very long strings, the intermediate list may be a
+;   problem. A more space-aware implementation collect the characters 
+;   in an intermediate list and when this list becomes too large it is
+;   converted into an intermediate string. At the end, the intermediate
+;   strings are concatenated with string-append.
+
+
+(define-syntax string-append-ec
+  (syntax-rules ()
+    ((string-append-ec etc1 etc ...)
+     (apply string-append (list-ec etc1 etc ...)) )))
+
+(define-syntax vector-ec
+  (syntax-rules ()
+    ((vector-ec etc1 etc ...)
+     (list->vector (list-ec etc1 etc ...)) )))
+
+; Comment: A similar approach as for string-ec can be used for vector-ec.
+;   However, the space overhead for the intermediate list is much lower
+;   than for string-ec and as there is no vector-append, the intermediate
+;   vectors must be copied explicitly.
+
+(define-syntax vector-of-length-ec
+  (syntax-rules (nested)
+    ((vector-of-length-ec k (nested q1 ...) q etc1 etc ...)
+     (vector-of-length-ec k (nested q1 ... q) etc1 etc ...) )
+    ((vector-of-length-ec k q1 q2             etc1 etc ...)
+     (vector-of-length-ec k (nested q1 q2)    etc1 etc ...) )
+    ((vector-of-length-ec k expression)
+     (vector-of-length-ec k (nested) expression) )
+
+    ((vector-of-length-ec k qualifier expression)
+     (let ((len k))
+       (let ((vec (make-vector len))
+             (i 0) )
+         (do-ec qualifier
+                (if (< i len)
+                    (begin (vector-set! vec i expression)
+                           (set! i (+ i 1)) )
+                    (error "vector is too short for the comprehension") ))
+         (if (= i len)
+             vec
+             (error "vector is too long for the comprehension") ))))))
+
+
+(define-syntax sum-ec
+  (syntax-rules ()
+    ((sum-ec etc1 etc ...)
+     (fold-ec (+) etc1 etc ... +) )))
+
+(define-syntax product-ec
+  (syntax-rules ()
+    ((product-ec etc1 etc ...)
+     (fold-ec (*) etc1 etc ... *) )))
+
+(define-syntax min-ec
+  (syntax-rules ()
+    ((min-ec etc1 etc ...)
+     (fold3-ec (min) etc1 etc ... min min) )))
+
+(define-syntax max-ec
+  (syntax-rules ()
+    ((max-ec etc1 etc ...)
+     (fold3-ec (max) etc1 etc ... max max) )))
+
+(define-syntax last-ec
+  (syntax-rules (nested)
+    ((last-ec default (nested q1 ...) q etc1 etc ...)
+     (last-ec default (nested q1 ... q) etc1 etc ...) )
+    ((last-ec default q1 q2             etc1 etc ...)
+     (last-ec default (nested q1 q2)    etc1 etc ...) )
+    ((last-ec default expression)
+     (last-ec default (nested) expression) )
+
+    ((last-ec default qualifier expression)
+     (let ((result default))
+       (do-ec qualifier (set! result expression))
+       result ))))
+
+
+; ==========================================================================
+; The fundamental early-stopping comprehension first-ec
+; ==========================================================================
+
+(define-syntax first-ec
+  (syntax-rules (nested)
+    ((first-ec default (nested q1 ...) q etc1 etc ...)
+     (first-ec default (nested q1 ... q) etc1 etc ...) )
+    ((first-ec default q1 q2             etc1 etc ...)
+     (first-ec default (nested q1 q2)    etc1 etc ...) )
+    ((first-ec default expression)
+     (first-ec default (nested) expression) )
+
+    ((first-ec default qualifier expression)
+     (let ((result default) (stop #f))
+       (ec-guarded-do-ec 
+         stop 
+         (nested qualifier)
+         (begin (set! result expression)
+                (set! stop #t) ))
+       result ))))
+
+; (ec-guarded-do-ec stop (nested q ...) cmd)
+;   constructs (do-ec q ... cmd) where the generators gen in q ... are
+;   replaced by (:until gen stop).
+
+(define-syntax ec-guarded-do-ec
+  (syntax-rules (nested if not and or begin)
+
+    ((ec-guarded-do-ec stop (nested (nested q1 ...) q2 ...) cmd)
+     (ec-guarded-do-ec stop (nested q1 ... q2 ...) cmd) )
+
+    ((ec-guarded-do-ec stop (nested (if test) q ...) cmd)
+     (if test (ec-guarded-do-ec stop (nested q ...) cmd)) )
+    ((ec-guarded-do-ec stop (nested (not test) q ...) cmd)
+     (if (not test) (ec-guarded-do-ec stop (nested q ...) cmd)) )
+    ((ec-guarded-do-ec stop (nested (and test ...) q ...) cmd)
+     (if (and test ...) (ec-guarded-do-ec stop (nested q ...) cmd)) )
+    ((ec-guarded-do-ec stop (nested (or test ...) q ...) cmd)
+     (if (or test ...) (ec-guarded-do-ec stop (nested q ...) cmd)) )
+
+    ((ec-guarded-do-ec stop (nested (begin etc ...) q ...) cmd)
+     (begin etc ... (ec-guarded-do-ec stop (nested q ...) cmd)) )
+
+    ((ec-guarded-do-ec stop (nested gen q ...) cmd)
+     (do-ec 
+       (:until gen stop) 
+       (ec-guarded-do-ec stop (nested q ...) cmd) ))
+
+    ((ec-guarded-do-ec stop (nested) cmd)
+     (do-ec cmd) )))
+
+; Alternative: Instead of modifying the generator with :until, it is
+;   possible to use call-with-current-continuation:
+;
+;   (define-synatx first-ec 
+;     ...same as above...
+;     ((first-ec default qualifier expression)
+;      (call-with-current-continuation 
+;       (lambda (cc)
+;        (do-ec qualifier (cc expression))
+;        default ))) ))
+;
+;   This is much simpler but not necessarily as efficient.
+
+
+; ==========================================================================
+; The early-stopping comprehensions any?-ec every?-ec
+; ==========================================================================
+
+(define-syntax any?-ec
+  (syntax-rules (nested)
+    ((any?-ec (nested q1 ...) q etc1 etc ...)
+     (any?-ec (nested q1 ... q) etc1 etc ...) )
+    ((any?-ec q1 q2             etc1 etc ...)
+     (any?-ec (nested q1 q2)    etc1 etc ...) )
+    ((any?-ec expression)
+     (any?-ec (nested) expression) )
+
+    ((any?-ec qualifier expression)
+     (first-ec #f qualifier (if expression) #t) )))
+
+(define-syntax every?-ec
+  (syntax-rules (nested)
+    ((every?-ec (nested q1 ...) q etc1 etc ...)
+     (every?-ec (nested q1 ... q) etc1 etc ...) )
+    ((every?-ec q1 q2             etc1 etc ...)
+     (every?-ec (nested q1 q2)    etc1 etc ...) )
+    ((every?-ec expression)
+     (every?-ec (nested) expression) )
+
+    ((every?-ec qualifier expression)
+     (first-ec #t qualifier (if (not expression)) #f) )))
+
diff --git a/test-suite/Makefile.am b/test-suite/Makefile.am
index 22f31d9..a481260 100644
--- a/test-suite/Makefile.am
+++ b/test-suite/Makefile.am
@@ -119,6 +119,7 @@ SCM_TESTS = tests/00-initial-env.test               \
            tests/srfi-35.test                  \
            tests/srfi-37.test                  \
            tests/srfi-39.test                  \
+           tests/srfi-42.test                  \
            tests/srfi-60.test                  \
            tests/srfi-69.test                  \
            tests/srfi-88.test                  \
diff --git a/test-suite/tests/srfi-42.test b/test-suite/tests/srfi-42.test
new file mode 100644
index 0000000..5417de0
--- /dev/null
+++ b/test-suite/tests/srfi-42.test
@@ -0,0 +1,618 @@
+;;; -*- mode: scheme; coding: utf-8; -*-
+
+;;; Examples for Eager Comprehensions in [outer..inner|expr]-Convention
+;;; ===================================================================
+;;;
+;;; Copyright (C) 2010 Free Software Foundation, Inc.
+;;; Copyright (c) 2007 Sebastian Egner
+;;;
+;;; This code is based on the file examples.scm in the reference
+;;; implementation of SRFI-42, provided under the following license:
+;;;
+;;; Permission is hereby granted, free of charge, to any person obtaining
+;;; a copy of this software and associated documentation files (the
+;;; ``Software''), to deal in the Software without restriction, including
+;;; without limitation the rights to use, copy, modify, merge, publish,
+;;; distribute, sublicense, and/or sell copies of the Software, and to
+;;; permit persons to whom the Software is furnished to do so, subject to
+;;; the following conditions:
+;;; 
+;;; The above copyright notice and this permission notice shall be
+;;; included in all copies or substantial portions of the Software.
+;;; 
+;;; THE SOFTWARE IS PROVIDED ``AS IS'', WITHOUT WARRANTY OF ANY KIND,
+;;; EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+;;; MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+;;; NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
+;;; LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+;;; OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+;;; WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+;;; 
+
+(define-module (test-srfi-42)
+  #:use-module (test-suite lib)
+  #:use-module (srfi srfi-42))
+
+
+; Tools for checking results
+; ==========================
+
+(define (my-equal? x y)
+  (cond
+   ((or (boolean? x) 
+        (null? x)
+        (symbol? x) 
+        (char? x) 
+        (input-port? x)
+        (output-port? x) )
+    (eqv? x y) )
+   ((string? x)
+    (and (string? y) (string=? x y)) )
+   ((vector? x)
+    (and (vector? y)
+         (my-equal? (vector->list x) (vector->list y)) ))
+   ((pair? x)
+    (and (pair? y)
+         (my-equal? (car x) (car y))
+         (my-equal? (cdr x) (cdr y)) ))
+   ((real? x)
+    (and (real? y)
+         (eqv? (exact? x) (exact? y))
+         (if (exact? x)
+             (= x y)
+             (< (abs (- x y)) (/ 1 (expt 10 6))) ))) ; will do here
+   (else
+    (error "unrecognized type" x) )))
+
+(define-syntax my-check
+  (syntax-rules (=>)
+    ((my-check ec => desired-result)
+     (pass-if (my-equal? ec desired-result)))))
+
+(define my-call-with-input-file call-with-input-file)
+(define my-open-output-file open-output-file)
+
+; ==========================================================================
+; do-ec 
+; ==========================================================================
+
+(my-check 
+  (let ((x 0)) (do-ec (set! x (+ x 1))) x) 
+  => 1)
+
+(my-check 
+  (let ((x 0)) (do-ec (:range i 10) (set! x (+ x 1))) x) 
+  => 10)
+
+(my-check 
+  (let ((x 0)) (do-ec (:range n 10) (:range k n) (set! x (+ x 1))) x) 
+  => 45)
+
+
+; ==========================================================================
+; list-ec and basic qualifiers 
+; ==========================================================================
+
+(my-check (list-ec 1) => '(1))
+
+(my-check (list-ec (:range i 4) i) => '(0 1 2 3))
+
+(my-check (list-ec (:range n 3) (:range k (+ n 1)) (list n k)) 
+  => '((0 0) (1 0) (1 1) (2 0) (2 1) (2 2)) )
+
+(my-check 
+  (list-ec (:range n 5) (if (even? n)) (:range k (+ n 1)) (list n k)) 
+  => '((0 0) (2 0) (2 1) (2 2) (4 0) (4 1) (4 2) (4 3) (4 4)) )
+
+(my-check 
+  (list-ec (:range n 5) (not (even? n)) (:range k (+ n 1)) (list n k)) 
+  => '((1 0) (1 1) (3 0) (3 1) (3 2) (3 3)) )
+
+(my-check
+  (list-ec (:range n 5) 
+           (and (even? n) (> n 2)) 
+           (:range k (+ n 1)) 
+           (list n k) )
+  => '((4 0) (4 1) (4 2) (4 3) (4 4)) )
+
+(my-check
+  (list-ec (:range n 5) 
+           (or (even? n) (> n 3)) 
+           (:range k (+ n 1)) 
+           (list n k) )
+  => '((0 0) (2 0) (2 1) (2 2) (4 0) (4 1) (4 2) (4 3) (4 4)) )
+
+(my-check
+ (let ((x 0)) (list-ec (:range n 10) (begin (set! x (+ x 1))) n) x)
+ => 10 )
+
+(my-check
+ (list-ec (nested (:range n 3) (:range k n)) k)
+ => '(0 0 1) )
+
+
+; ==========================================================================
+; Other comprehensions
+; ==========================================================================
+
+(my-check (append-ec '(a b)) => '(a b))
+(my-check (append-ec (:range i 0) '(a b)) => '())
+(my-check (append-ec (:range i 1) '(a b)) => '(a b))
+(my-check (append-ec (:range i 2) '(a b)) => '(a b a b))
+
+(my-check (string-ec #\a) => (string #\a))
+(my-check (string-ec (:range i 0) #\a) => "")
+(my-check (string-ec (:range i 1) #\a) => "a")
+(my-check (string-ec (:range i 2) #\a) => "aa")
+
+(my-check (string-append-ec "ab") => "ab")
+(my-check (string-append-ec (:range i 0) "ab") => "")
+(my-check (string-append-ec (:range i 1) "ab") => "ab")
+(my-check (string-append-ec (:range i 2) "ab") => "abab")
+
+(my-check (vector-ec 1) => (vector 1))
+(my-check (vector-ec (:range i 0) i) => (vector))
+(my-check (vector-ec (:range i 1) i) => (vector 0))
+(my-check (vector-ec (:range i 2) i) => (vector 0 1))
+
+(my-check (vector-of-length-ec 1 1) => (vector 1))
+(my-check (vector-of-length-ec 0 (:range i 0) i) => (vector))
+(my-check (vector-of-length-ec 1 (:range i 1) i) => (vector 0))
+(my-check (vector-of-length-ec 2 (:range i 2) i) => (vector 0 1))
+
+(my-check (sum-ec 1) => 1)
+(my-check (sum-ec (:range i 0) i) => 0)
+(my-check (sum-ec (:range i 1) i) => 0)
+(my-check (sum-ec (:range i 2) i) => 1)
+(my-check (sum-ec (:range i 3) i) => 3)
+
+(my-check (product-ec 1) => 1)
+(my-check (product-ec (:range i 1 0) i) => 1)
+(my-check (product-ec (:range i 1 1) i) => 1)
+(my-check (product-ec (:range i 1 2) i) => 1)
+(my-check (product-ec (:range i 1 3) i) => 2)
+(my-check (product-ec (:range i 1 4) i) => 6)
+
+(my-check (min-ec 1) => 1)
+(my-check (min-ec (:range i 1) i) => 0)
+(my-check (min-ec (:range i 2) i) => 0)
+
+(my-check (max-ec 1) => 1)
+(my-check (max-ec (:range i 1) i) => 0)
+(my-check (max-ec (:range i 2) i) => 1)
+
+(my-check (first-ec #f 1) => 1)
+(my-check (first-ec #f (:range i 0) i) => #f)
+(my-check (first-ec #f (:range i 1) i) => 0)
+(my-check (first-ec #f (:range i 2) i) => 0)
+
+(my-check 
+  (let ((last-i -1))
+    (first-ec #f (:range i 10) (begin (set! last-i i)) i)
+    last-i )
+  => 0 )
+
+(my-check (last-ec #f 1) => 1)
+(my-check (last-ec #f (:range i 0) i) => #f)
+(my-check (last-ec #f (:range i 1) i) => 0)
+(my-check (last-ec #f (:range i 2) i) => 1)
+
+(my-check (any?-ec #f) => #f)
+(my-check (any?-ec #t) => #t)
+(my-check (any?-ec (:range i 2 2) (even? i)) => #f)
+(my-check (any?-ec (:range i 2 3) (even? i)) => #t)
+
+(my-check (every?-ec #f) => #f)
+(my-check (every?-ec #t) => #t)
+(my-check (every?-ec (:range i 2 2) (even? i)) => #t)
+(my-check (every?-ec (:range i 2 3) (even? i)) => #t)
+(my-check (every?-ec (:range i 2 4) (even? i)) => #f)
+
+(my-check 
+ (let ((sum-sqr (lambda (x result) (+ result (* x x)))))
+   (fold-ec 0 (:range i 10) i sum-sqr) )
+ => 285 )
+
+(my-check 
+ (let ((minus-1 (lambda (x) (- x 1)))
+       (sum-sqr (lambda (x result) (+ result (* x x)))))
+   (fold3-ec (error "wrong") (:range i 10) i minus-1 sum-sqr) )
+ => 284 )
+
+(my-check 
+ (fold3-ec 'infinity (:range i 0) i min min)
+ => 'infinity )
+
+
+; ==========================================================================
+; Typed generators
+; ==========================================================================
+
+(my-check (list-ec (:list x '()) x) => '())
+(my-check (list-ec (:list x '(1)) x) => '(1))
+(my-check (list-ec (:list x '(1 2 3)) x) => '(1 2 3))
+(my-check (list-ec (:list x '(1) '(2)) x) => '(1 2))
+(my-check (list-ec (:list x '(1) '(2) '(3)) x) => '(1 2 3))
+
+(my-check (list-ec (:string c "") c) => '())
+(my-check (list-ec (:string c "1") c) => '(#\1))
+(my-check (list-ec (:string c "123") c) => '(#\1 #\2 #\3))
+(my-check (list-ec (:string c "1" "2") c) => '(#\1 #\2))
+(my-check (list-ec (:string c "1" "2" "3") c) => '(#\1 #\2 #\3))
+
+(my-check (list-ec (:vector x (vector)) x) => '())
+(my-check (list-ec (:vector x (vector 1)) x) => '(1))
+(my-check (list-ec (:vector x (vector 1 2 3)) x) => '(1 2 3))
+(my-check (list-ec (:vector x (vector 1) (vector 2)) x) => '(1 2))
+(my-check 
+ (list-ec (:vector x (vector 1) (vector 2) (vector 3)) x)
+ => '(1 2 3))
+
+(my-check (list-ec (:range x -2) x) => '())
+(my-check (list-ec (:range x -1) x) => '())
+(my-check (list-ec (:range x  0) x) => '())
+(my-check (list-ec (:range x  1) x) => '(0))
+(my-check (list-ec (:range x  2) x) => '(0 1))
+
+(my-check (list-ec (:range x  0  3) x) => '(0 1 2))
+(my-check (list-ec (:range x  1  3) x) => '(1 2))
+(my-check (list-ec (:range x -2 -1) x) => '(-2))
+(my-check (list-ec (:range x -2 -2) x) => '())
+
+(my-check (list-ec (:range x 1 5  2) x) => '(1 3))
+(my-check (list-ec (:range x 1 6  2) x) => '(1 3 5))
+(my-check (list-ec (:range x 5 1 -2) x) => '(5 3))
+(my-check (list-ec (:range x 6 1 -2) x) => '(6 4 2))
+
+(my-check (list-ec (:real-range x 0.0 3.0)     x) => '(0. 1. 2.))
+(my-check (list-ec (:real-range x 0   3.0)     x) => '(0. 1. 2.))
+(my-check (list-ec (:real-range x 0   3   1.0) x) => '(0. 1. 2.))
+
+(my-check 
+ (string-ec (:char-range c #\a #\z) c) 
+ => "abcdefghijklmnopqrstuvwxyz" )
+
+(my-check 
+ (begin
+   (let ((f (my-open-output-file "tmp1")))
+     (do-ec (:range n 10) (begin (write n f) (newline f)))
+     (close-output-port f))
+   (my-call-with-input-file "tmp1"
+    (lambda (port) (list-ec (:port x port read) x)) ))
+ => (list-ec (:range n 10) n) )
+
+(my-check 
+ (begin
+   (let ((f (my-open-output-file "tmp1")))
+     (do-ec (:range n 10) (begin (write n f) (newline f)))
+     (close-output-port f))
+   (my-call-with-input-file "tmp1"                 
+     (lambda (port) (list-ec (:port x port) x)) ))
+ => (list-ec (:range n 10) n) )
+
+
+; ==========================================================================
+; The special generators :do :let :parallel :while :until
+; ==========================================================================
+
+(my-check (list-ec (:do ((i 0)) (< i 4) ((+ i 1))) i) => '(0 1 2 3))
+
+(my-check 
+ (list-ec 
+  (:do (let ((x 'x)))
+       ((i 0)) 
+       (< i 4) 
+       (let ((j (- 10 i))))
+       #t
+       ((+ i 1)) )
+  j )
+ => '(10 9 8 7) )
+
+(my-check (list-ec (:let x 1) x) => '(1))
+(my-check (list-ec (:let x 1) (:let y (+ x 1)) y) => '(2))
+(my-check (list-ec (:let x 1) (:let x (+ x 1)) x) => '(2))
+
+(my-check 
+ (list-ec (:parallel (:range i 1 10) (:list x '(a b c))) (list i x))
+ => '((1 a) (2 b) (3 c)) )
+
+(my-check 
+ (list-ec (:while (:range i 1 10) (< i 5)) i)
+ => '(1 2 3 4) )
+
+(my-check 
+ (list-ec (:until (:range i 1 10) (>= i 5)) i)
+ => '(1 2 3 4 5) )
+
+; with generator that might use inner bindings
+
+(my-check
+ (list-ec (:while (:list i '(1 2 3 4 5 6 7 8 9)) (< i 5)) i)
+ => '(1 2 3 4) )
+; Was broken in original reference implementation as pointed
+; out by address@hidden on 24-Apr-2005 comp.lang.scheme.
+; Refer to http://groups-beta.google.com/group/comp.lang.scheme/
+; browse_thread/thread/f5333220eaeeed66/75926634cf31c038#75926634cf31c038
+
+(my-check 
+ (list-ec (:until (:list i '(1 2 3 4 5 6 7 8 9)) (>= i 5)) i)
+ => '(1 2 3 4 5) )
+
+(my-check
+ (list-ec (:while (:vector x (index i) '#(1 2 3 4 5))
+                 (< x 10))
+         x)
+ => '(1 2 3 4 5))
+; Was broken in reference implementation, even after fix for the
+; bug reported by Sunnan, as reported by Jens-Axel Soegaard on
+; 4-Jun-2007.
+
+; combine :while/:until and :parallel
+
+(my-check
+ (list-ec (:while (:parallel (:range i 1 10)
+                             (:list j '(1 2 3 4 5 6 7 8 9)))
+                  (< i 5))
+          (list i j))
+ => '((1 1) (2 2) (3 3) (4 4)))
+
+(my-check
+ (list-ec (:until (:parallel (:range i 1 10)
+                             (:list j '(1 2 3 4 5 6 7 8 9)))
+                  (>= i 5))
+          (list i j))
+ => '((1 1) (2 2) (3 3) (4 4) (5 5)))
+
+; check that :while/:until really stop the generator
+
+(my-check
+ (let ((n 0))
+   (do-ec (:while (:range i 1 10) (begin (set! n (+ n 1)) (< i 5)))
+          (if #f #f))
+   n)
+ => 5)
+
+(my-check
+ (let ((n 0))
+   (do-ec (:until (:range i 1 10) (begin (set! n (+ n 1)) (>= i 5)))
+          (if #f #f))
+   n)
+ => 5)
+
+(my-check
+ (let ((n 0))
+   (do-ec (:while (:parallel (:range i 1 10)
+                             (:do () (begin (set! n (+ n 1)) #t) ()))
+                  (< i 5))
+          (if #f #f))
+   n)
+ => 5)
+
+(my-check
+ (let ((n 0))
+   (do-ec (:until (:parallel (:range i 1 10)
+                             (:do () (begin (set! n (+ n 1)) #t) ()))
+                  (>= i 5))
+          (if #f #f))
+   n)
+ => 5)
+
+; ==========================================================================
+; The dispatching generator
+; ==========================================================================
+
+(my-check (list-ec (: c '(a b)) c) => '(a b))
+(my-check (list-ec (: c '(a b) '(c d)) c) => '(a b c d))
+
+(my-check (list-ec (: c "ab") c) => '(#\a #\b))
+(my-check (list-ec (: c "ab" "cd") c) => '(#\a #\b #\c #\d))
+
+(my-check (list-ec (: c (vector 'a 'b)) c) => '(a b))
+(my-check (list-ec (: c (vector 'a 'b) (vector 'c)) c) => '(a b c))
+
+(my-check (list-ec (: i 0) i) => '())
+(my-check (list-ec (: i 1) i) => '(0))
+(my-check (list-ec (: i 10) i) => '(0 1 2 3 4 5 6 7 8 9))
+(my-check (list-ec (: i 1 2) i) => '(1))
+(my-check (list-ec (: i 1 2 3) i) => '(1))
+(my-check (list-ec (: i 1 9 3) i) => '(1 4 7))
+
+(my-check (list-ec (: i 0.0 1.0 0.2) i) => '(0. 0.2 0.4 0.6 0.8))
+
+(my-check (list-ec (: c #\a #\c) c) => '(#\a #\b #\c))
+
+(my-check 
+ (begin
+   (let ((f (my-open-output-file "tmp1")))
+     (do-ec (:range n 10) (begin (write n f) (newline f)))
+     (close-output-port f))
+   (my-call-with-input-file "tmp1"                 
+     (lambda (port) (list-ec (: x port read) x)) ))
+ => (list-ec (:range n 10) n) )
+    
+(my-check 
+ (begin
+   (let ((f (my-open-output-file "tmp1")))
+     (do-ec (:range n 10) (begin (write n f) (newline f)))
+     (close-output-port f))
+   (my-call-with-input-file "tmp1"                 
+     (lambda (port) (list-ec (: x port) x)) ))
+ => (list-ec (:range n 10) n) )
+
+
+; ==========================================================================
+; With index variable
+; ==========================================================================
+
+(my-check (list-ec (:list c (index i) '(a b)) (list c i)) => '((a 0) (b 1)))
+(my-check (list-ec (:string c (index i) "a") (list c i)) => '((#\a 0)))
+(my-check (list-ec (:vector c (index i) (vector 'a)) (list c i)) => '((a 0)))
+
+(my-check 
+ (list-ec (:range i (index j) 0 -3 -1) (list i j)) 
+ => '((0 0) (-1 1) (-2 2)) )
+
+(my-check 
+ (list-ec (:real-range i (index j) 0 1 0.2) (list i j)) 
+ => '((0. 0) (0.2 1) (0.4 2) (0.6 3) (0.8 4)) )
+
+(my-check 
+ (list-ec (:char-range c (index i) #\a #\c) (list c i)) 
+ => '((#\a 0) (#\b 1) (#\c 2)) )
+
+(my-check 
+ (list-ec (: x (index i) '(a b c d)) (list x i))
+ => '((a 0) (b 1) (c 2) (d 3)) )
+
+(my-check 
+ (begin
+   (let ((f (my-open-output-file "tmp1")))
+     (do-ec (:range n 10) (begin (write n f) (newline f)))
+     (close-output-port f))
+   (my-call-with-input-file "tmp1"
+     (lambda (port) (list-ec (: x (index i) port) (list x i))) ))
+ => '((0 0) (1 1) (2 2) (3 3) (4 4) (5 5) (6 6) (7 7) (8 8) (9 9)) )
+
+
+; ==========================================================================
+; The examples from the SRFI document
+; ==========================================================================
+
+; from Abstract
+
+(my-check (list-ec (: i 5) (* i i)) => '(0 1 4 9 16))
+
+(my-check 
+  (list-ec (: n 1 4) (: i n) (list n i)) 
+  => '((1 0) (2 0) (2 1) (3 0) (3 1) (3 2)) )
+
+; from Generators
+
+(my-check 
+  (list-ec (: x (index i) "abc") (list x i)) 
+  => '((#\a 0) (#\b 1) (#\c 2)) )
+
+(my-check
+  (list-ec (:string c (index i) "a" "b") (cons c i))
+  => '((#\a . 0) (#\b . 1)) )
+
+
+; ==========================================================================
+; Little Shop of Horrors
+; ==========================================================================
+
+(my-check (list-ec (:range x 5) (:range x x) x) => '(0 0 1 0 1 2 0 1 2 3))
+
+(my-check (list-ec (:list x '(2 "23" (4))) (: y x) y) => '(0 1 #\2 #\3 4))
+
+(my-check 
+ (list-ec (:parallel (:integers x) 
+                     (:do ((i 10)) (< x i) ((- i 1))))
+          (list x i))
+ => '((0 10) (1 9) (2 8) (3 7) (4 6)) )
+
+
+; ==========================================================================
+; Less artificial examples
+; ==========================================================================
+
+(define (factorial n) ; n * (n-1) * .. * 1 for n >= 0
+  (product-ec (:range k 2 (+ n 1)) k) )
+
+(my-check (factorial  0) => 1)
+(my-check (factorial  1) => 1)
+(my-check (factorial  3) => 6)
+(my-check (factorial  5) => 120)
+
+
+(define (eratosthenes n) ; primes in {2..n-1} for n >= 1
+  (let ((p? (make-string n #\1)))
+    (do-ec (:range k 2 n)
+           (if (char=? (string-ref p? k) #\1))
+           (:range i (* 2 k) n k)
+           (string-set! p? i #\0) )
+    (list-ec (:range k 2 n) (if (char=? (string-ref p? k) #\1)) k) ))
+
+(my-check 
+ (eratosthenes 50)
+ => '(2 3 5 7 11 13 17 19 23 29 31 37 41 43 47) )
+
+(my-check
+ (length (eratosthenes 100000))
+ => 9592 ) ; we expect 10^5/ln(10^5)
+
+
+(define (pythagoras n) ; a, b, c s.t. 1 <= a <= b <= c <= n, a^2 + b^2 = c^2
+  (list-ec 
+   (:let sqr-n (* n n))
+   (:range a 1 (+ n 1))
+; (begin (display a) (display " "))
+   (:let sqr-a (* a a))
+   (:range b a (+ n 1)) 
+   (:let sqr-c (+ sqr-a (* b b)))
+   (if (<= sqr-c sqr-n))
+   (:range c b (+ n 1))
+   (if (= (* c c) sqr-c))
+   (list a b c) ))
+           
+(my-check
+ (pythagoras 15)
+ => '((3 4 5) (5 12 13) (6 8 10) (9 12 15)) )
+
+(my-check
+ (length (pythagoras 200))
+ => 127 )
+
+
+(define (qsort xs) ; stable
+  (if (null? xs)
+      '()
+      (let ((pivot (car xs)) (xrest (cdr xs)))
+        (append
+         (qsort (list-ec (:list x xrest) (if (<  x pivot)) x))
+         (list pivot)
+         (qsort (list-ec (:list x xrest) (if (>= x pivot)) x)) ))))
+
+(my-check 
+ (qsort '(1 5 4 2 4 5 3 2 1 3))
+ => '(1 1 2 2 3 3 4 4 5 5) )
+
+
+(define (pi-BBP m) ; approx. of pi within 16^-m (Bailey-Borwein-Plouffe)
+  (sum-ec 
+    (:range n 0 (+ m 1))
+    (:let n8 (* 8 n))
+    (* (- (/ 4 (+ n8 1))
+          (+ (/ 2 (+ n8 4))
+             (/ 1 (+ n8 5))
+             (/ 1 (+ n8 6))))
+       (/ 1 (expt 16 n)) )))
+
+(my-check
+ (pi-BBP 5)
+ => (/ 40413742330349316707 12864093722915635200) )
+
+
+(define (read-line port) ; next line (incl. #\newline) of port
+  (let ((line
+         (string-ec 
+          (:until (:port c port read-char)
+                  (char=? c #\newline) )
+          c )))
+    (if (string=? line "")
+        (read-char port) ; eof-object
+        line )))
+
+(define (read-lines filename) ; list of all lines
+  (my-call-with-input-file 
+   filename
+   (lambda (port)
+     (list-ec (:port line port read-line) line) )))
+
+(my-check
+ (begin
+   (let ((f (my-open-output-file "tmp1")))
+     (do-ec (:range n 10) (begin (write n f) (newline f)))
+     (close-output-port f))
+   (read-lines "tmp1") )
+ => (list-ec (:char-range c #\0 #\9) (string c #\newline)) )


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