Looking into Image locking problems [1] caused by a recursive array such as this... literalArray := #( 1 2 3 ). literalArray at: 3 put: literalArray. I find that "literalArray printString" locks the image due to Array>>printOn: use of the recursive #shouldBePrintedAsLiteral method. Now its implementation is identical to #isLiteral and indeed "literalArray isLiteral" also locks the Image. So comparing implementors of #isLiteral... Object>>isLiteral ^false Boolean>>isLiteral ^true Character>>isLiteral ^true Integer>>isLiteral ^true String>>isLiteral ^true UndefinedObject>>isLiteral ^true ByteArray>>isLiteral ^self class == ByteArray Float>>isLiteral ^self isFinite "^(self - self) = 0.0" ScaledDecimal>>isLiteral ^denominator = 1 or: [(10 raisedTo: scale)\\denominator = 0] Array>>isLiteral ^self class == Array and: [self allSatisfy: [:each | each isLiteral]] ...I find most are very basic (might even say deterministic), with the recursion of Array>>isLiteral seeming an annomaly. Also, the big IF condition in Array>>printOn: smells like a design decision being made at runtime (Valloud AMCOS p12). Array>>printOn: aStream self shouldBePrintedAsLiteral ifTrue: [self printAsLiteralFormOn: aStream. ^ self]. self isSelfEvaluating ifTrue: [self printAsSelfEvaluatingFormOn: aStream. ^ self]. super printOn: aStream Flipping between two printString formats seems like selecting between two class types. Indeed, if we had a LiteralArray class, there would be no need for its printOn: to recursively search to determine its form, thus allowing #printStringLimitedTo: to do its thing to protect against infinite recursion. Also, instead of a recursive Array>>isLiteral we'd have something like LiteralArray>>isLiteral ^true Array>>isLiteral ^false which seems to align much better with the pattern of the other #isLiteral implementors. I notice there is both RBArrayNode and RBLiteralArrayNode. So what are the wider concerns that might apply? (In particular, I'm not sure how the #isSelfEvaluating (which is also recursive) fits into the big picture) cheers -ben [1] https://www.mail-archive.com/pharo-dev@lists.pharo.org/msg25156.html