Chris Muller uploaded a new version of Collections to project The Trunk:
http://source.squeak.org/trunk/Collections-cmm.785.mcz

==================== Summary ====================

Name: Collections-cmm.785
Author: cmm
Time: 30 March 2018, 5:57:37.727038 pm
UUID: 37e9870a-5379-4185-8538-fada710dad5d
Ancestors: Collections-eem.784

Add #at:ifPresent:ifAbsent: for API compatibility with other kinds of directly-accessible Collections.

=============== Diff against Collections-eem.784 ===============

Item was added:
+ ----- Method: SequenceableCollection>>at:ifPresent:ifAbsent: (in category 'accessing') -----
+ at: index ifPresent: elementBlock ifAbsent: exceptionBlock
+       "Answer the value of elementBlock on the element at position index.  If I do not contain an element at index, answer the result of evaluating exceptionBlock."
+       ^ elementBlock value:
+               (self
+                       at: index
+                       ifAbsent: [ ^ exceptionBlock value ])!