Is there a portable (that would work in GemStone too) and safe way to know if a String would be a block?��

I must support this kind of strings:

'singleString' �� -> false

'multi string' -> false

' �� �� ��[:a | 42]' -> true

' �� '' '' ��[:a | 42]' -> true

'[:a | 42]' -> true

' "a commet" [:a | 42]' -> true

' WhateverClass someVeryBadHackishMethod. [:a | 42]' -> true��

I need to identify whether the string is a closure or not. And ideally, I don't want to do an #evaluate: because I don't want any left hand code to be executed.��
I tried with #parse: ��why I am having problems.��

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