The non-deterministic local choice operator
s1 + s2 chooses one of the strategies
s1 or
s2 to apply. If the one chose fails, the other one is tried.
The
+ operator is
local because once one of the strategies has succeeded the choice is committed, even if the continuation of the choice fails on the result. If backtracking to the other strategy is desired one should used the
GlobalChoice? operator
++.
The
+ operator is
non-determinstic sine the
EvaluationOrder in which the strategies are tried is
not defined. The
StrategoCompiler is free to choose an order. If complete control over the evaluation order
is needed one should use the
DeterministicChoice operator
<-.
In Stratego it is permitted to define several
RewriteRules with the same label. This interpreted as the
composition with
+ of the rules.
It would be useful to
DetectOverlappingRules in a non-deterministic choice.
--
EelcoVisser - 17 Mar 2002
CategoryGlossary |
StrategoGlossary