refactor tests, add working code for list

1 files changed, 87 insertions, 0 deletions

diff --git a/mcgoron.iterator.list.scm b/mcgoron.iterator.list.scm
new file mode 100644
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+++ b/mcgoron.iterator.list.scm
@@ -0,0 +1,87 @@
+#| Copyright 2024 Peter McGoron
+ |
+ | Licensed under the Apache License, Version 2.0 (the "License");
+ | you may not use this file except in compliance with the License.
+ | You may obtain a copy of the License at
+ |
+ |     http://www.apache.org/licenses/LICENSE-2.0
+ |
+ | Unless required by applicable law or agreed to in writing, software
+ | distributed under the License is distributed on an "AS IS" BASIS,
+ | WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ | See the License for the specific language governing permissions and
+ | limitations under the License.
+ |-------------------------------------------------------------------------
+ | This is a list iterator that allows for mutation of the list.
+ |
+ | The list iterator is made up of
+ | * the `signifier`: the head of the list.
+ | * the `previous` values, which is a list of all cons cells prior to the
+ |   current cons cell, in reverse.
+ | * the index, which is the index of the current element in the list. This
+ |   is updated internally but not used internally, so the root index does
+ |   not have to be 0.
+ | * the `next` list, which is either empty or has as it's car the current
+ |   item.
+ |#
+
+(define (make-list-iterator signifier previous idx rest)
+  (when (not (or (pair? rest) (null? rest)))
+    (raise (improper-list-exception idx rest)))
+  (make-iterator
+   (lambda () (null? previous))
+   (lambda () (null? rest))
+   (lambda (num)
+     (cond
+       ((not (integer?))
+        (raise (non-integer-movement-exception spaces)))
+       ((negative? num)
+        (let loop ((cntr (- num))
+                   (previous previous)
+                   (rest rest))
+          (cond
+            ((= num 0) (make-list-iterator signifier
+                                           previous
+                                           (+ total num)
+                                           rest))
+            ((null? previous) #f)
+            (else (loop (- cntr 1)
+                        (cdr previous)
+                        (car previous))))))
+       (else
+        (let loop ((cntr num)
+                   (previous previous)
+                   (rest rest))
+          (cond
+            ((= num 0) (make-list-iterator signifier
+                                           previous
+                                           (+ total num)
+                                           rest))
+            ((null? rest) #f)
+            (else (loop (- 1 num)
+                        (cons rest previous)
+                        (cdr rest))))))))
+   (lambda ()
+     (if (null? rest)
+         (error "cannot ref end of list" previous rest)
+         (car rest)))
+   (lambda (predicate? other-iterators)
+     (let ((cmp (make-default-comparator)))
+       (iteratively-apply-predicate
+        (lambda (x y)
+          (predicate? cmp (get-private x) (get-private y)))
+        idx
+        other-iterators)))
+   idx))
+
+(define (list-iterator-start rest)
+  (make-list-iterator rest '() 0 rest))
+
+(define (list-iterator-to-end itr)
+  (if (iterator-end? itr)
+      itr
+      (list-iterator-to-end (iterator-advance itr 1))))
+
+(define (list-iterator-end lst)
+  (list-iterator-to-end (list-iterator-start lst)))
+