== operator freeze

[mario]

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Import the attached file from hugs and evaluate the following expression:

get ((AttributeLeaf (MyLabel "x") 4)::Env1) (MyLabel "x")

The result should be Just 4. But if you replace the operator =?= with the 
builtin operator == on line 31 and then retry the same expression, the 
evaluation diverges. The =?= operator is defined as

l =?= l' = l == l'

Since I have found this workaround (after two days of looking for bugs in my 
code) the matter is no longer urgent to me, but I'd like to know if and when 
you fix it. Thank you.

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