Colin Putney uploaded a new version of Collections to project The Trunk:
http://source.squeak.org/trunk/Collections-cwp.487.mcz

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

Name: Collections-cwp.487
Author: cwp
Time: 14 August 2012, 10:41:13.046 am
UUID: 3200b102-5364-462e-9664-94017891a1e3
Ancestors: Collections-cwp.486

Account for the fact that binary selectors can't include underscores. This means a single underscore must be considered an unary selector.

=============== Diff against Collections-cwp.485 ===============

Item was added:
+ ----- Method: Character>>canBeIdentifierInitial (in category 'testing') -----
+ canBeIdentifierInitial
+ 	^ self == $_ or: [self isLetter]!

Item was changed:
  ----- Method: Symbol>>precedence (in category 'accessing') -----
  precedence
  	"Answer the receiver's precedence, assuming it is a valid Smalltalk
  	message selector or 0 otherwise.  The numbers are 1 for unary,
  	2 for binary and 3 for keyword selectors."
  
+ 	self size = 0 ifTrue: [ ^ 0 ].
+ 	self first canBeIdentifierInitial ifFalse: [ ^ 2 ].
+ 	self last = $: ifTrue: [ ^ 3 ].
- 	self size = 0 ifTrue: [^ 0].
- 	self first isLetter ifFalse: [^ 2].
- 	self last = $: ifTrue: [^ 3].
  	^ 1!