I am looking at ifTrue: alternativeBlock "If the receiver is false (i.e., the condition is false), then the value is the false alternative, which is nil. Otherwise answer the result of evaluating the argument, alternativeBlock. Create an error notification if the receiver is nonBoolean. Execution does not actually reach here because the expression is compiled in-line." self subclassResponsibility In order to perform the block, ifTrue must somehow end up evaluating the block, but this code only sends a subclassResponsibility message to itself and implicitly returns itself. Where does the block actually get evaluated? -- View this message in context: http://forum.world.st/How-does-Boolean-ifTrue-work-tp4920873.html Sent from the Pharo Smalltalk Users mailing list archive at Nabble.com.