Contextual Rule
Stratego -- Strategies for Program Transformation
A contextual rule is a RewriteRule in which the left-hand side and right-hand side terms contain
contexts of the form x[t].
A typical example of a contextual rule is the following inlining rule:
Inline : Let(x, e1, e2[Var(x)]) -> Let(x, e1, e2[e1])The idea is that an occurrence of
Var(x) in =e2 is replaced with the term e1.
Contextual rules are treated as syntactic sugar and translated to a normal rule, which
performs a traversal over the context subterm. The inlining rule above is translated to
the rule:
Inline :
Let(x, e1, e2) -> Let(x, e1, e2')
where <oncetd(?Var(x); !e1)> e2 => e2'
The traversal strategy oncetd is used to find an occurrence of Var(x) and replace it
with e1. Note that in the match of Var(x), the variable x is already bound by the
match of the left-hand Let(x, e1, e2) side of the rule.
Issues
- traversal strategy
- multiple contexts
- conditions
- overlapping contextual rules
- backtracking
CategoryGlossary