配置中支持复杂配置逻辑（如：if else 的逻辑，模版变量，预定义变量）

[garyelephant]

conditional and expression in configurtion file:

example:

if [a.b.c != 3] {
	
} else {
	
}

references:

logstash configuration
http://enear.github.io/2016/03/31/parser-combinators/
https://github.com/sirthias/parboiled2
http://www.lihaoyi.com/fastparse/
https://gist.github.com/nicerobot/4189552
https://dzone.com/articles/rolling-your-own-dsl-in-scala
https://www.slideshare.net/abhijit.sharma/writing-dsls-in-scala
https://www.slideshare.net/holograph/a-field-guide-to-dsl-design-in-scala
http://jmespath.org/
http://www.antlr.org/

Search keyword: Grammars, workflows, DSL, expression, eval

[garyelephant]

目前已通过 antlr4在配置文件中支持了if else结构的配置和解析，但是体系代码中，还未加入if else的逻辑代码。