Interpreter

Interpreter[form] represents an interpreter object that can be applied to an input to try to interpret it as an object of the specified form. 

Interpreter[form,test] returns the interpreted object only if applying test to it yields True; otherwise it returns a Failure object.

Interpreter[form,test,fail] returns the result of applying the function fail if the test fails.

Please visit the official Wolfram Language Reference for more details and examples on core symbols.