Github user dawidwys commented on a diff in the pull request:

    https://github.com/apache/flink/pull/4331#discussion_r132384194
  
    --- Diff: 
flink-libraries/flink-cep/src/main/java/org/apache/flink/cep/nfa/compiler/NFACompiler.java
 ---
    @@ -150,6 +160,59 @@ long getWindowTime() {
                }
     
                /**
    +            * Check pattern after match skip strategy.
    +            */
    +           private void checkPatternSkipStrategy() {
    +                   AfterMatchSkipStrategy afterMatchSkipStrategy = 
currentPattern.getAfterMatchSkipStrategy();
    +                   if (afterMatchSkipStrategy.getStrategy() == 
AfterMatchSkipStrategy.SkipStrategy.SKIP_TO_FIRST ||
    +                           afterMatchSkipStrategy.getStrategy() == 
AfterMatchSkipStrategy.SkipStrategy.SKIP_TO_LAST) {
    +                           Pattern<T, ?> pattern = currentPattern;
    +                           while 
(!pattern.getName().equals(afterMatchSkipStrategy.getPatternName())) {
    +                                   pattern = pattern.getPrevious();
    +                           }
    +                           // pattern name match check.
    +                           if (pattern == null) {
    +                                   throw new 
MalformedPatternException("the pattern name specified in AfterMatchSkipStrategy 
" +
    +                                           "can not be found in the given 
Pattern");
    +                           } else {
    +                                   // can not be used with optional states.
    +                                   if 
(pattern.getQuantifier().hasProperty(Quantifier.QuantifierProperty.OPTIONAL)) {
    +                                           throw new 
MalformedPatternException("the AfterMatchSkipStrategy "
    +                                                   + 
afterMatchSkipStrategy.getStrategy() + " can not be used with optional 
pattern");
    +                                   }
    +                           }
    +
    +                           // start position check.
    +                           if (pattern.getPrevious() == null) {
    --- End diff --
    
    I personally see no reason for a semantic with RuntimeException. I can't 
think of any use-case for it. Maybe let's finish this PR without the switch and 
exceptions and open a JIRA with the switch, ideally with some use-case's for 
that semantic, so we can further agree on that and see if anyone needs it.


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