Something just occurred to me with regard to call by name. There are no SETS 
and USES  attributes in an Algol 60 parameter declaration. If a parameter is 
used as an l-value, there is a potential problem. A value like A[I} is 
legitimate on either side of an assignment, but a value like A[I]+1 is valid 
only on the right.

In languages with call by reference and with procedure parameters, this becomes 
a non-issue: A[I]+1 is not a valid reference.

Shmuel (Seymour J.) Metz

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