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The
idea behind this class is that, between the attributes associated with a
production body, dependency-graph edges can go from left to right, but not from
right to left(hence "L-attributed"). Each attribute must be either
1.
Synthesized, or
2.
Inherited, but with the rules limited as follows. Suppose that there is a
production A->X1
X2 • • • Xn, and that there is an inherited attribute Xi.a
computed by a rule associated with this production. Then the rule
may use only:
(a)
Inherited attributes associated with the head A.
(b)
Either inherited or synthesized attributes associated with the occurrences of symbols
X1 X2 • • • Xi-1 located to the left
of Xi
(c)
Inherited or synthesized attributes associated with this occurrence of Xi
itself,
but only in such a way that there are no cycles in a dependency graph formed by
the attributes of this Xi.
Example
1: The following definition is L-attributed. Here the inherited attribute of T_ gets
its values from its left sibling F. Similarly, T1_ gets
its value from its parent T_ and left sibling F.
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