Bots, like any other application, require use of expressions to evaluate outcome of a condition based on runtime information available in memory or to the dialog or the language generation system.
Common expression language was put together to address this core need as well as to rationalize and snap to a common expression language that will be used across Bot Framework SDK and other conversational AI components that need an expression language.
See API reference for Expression for API reference.
See Here for a complete list of prebuilt functions supported by the common expression language library.
If you changed the g4 file, please follow the instruction here to generate the new Lexer and Parser file. The specific command is:
java -jar antlr-4.11.1.jar -o Generated -Dlanguage=CSharp CommonRegex.g4 -visitor
java -jar antlr-4.11.1.jar -o Generated -Dlanguage=CSharp parser/ExpressionAntlrLexer.g4
java -jar antlr-4.11.1.jar -o Generated -Dlanguage=CSharp parser/ExpressionAntlrParser.g4 -visitor
antlr-4.11.1.jar presents the path of antlr jar.
xx.g4 presents the path of corresponding g4 file.
By the way, You will need to have a modern version of Java (>= JRE 1.6) to use it.