SQL & PL/SQL

Why aren't there functions like these?

IS_DATE(string,format)
IS_NUMBER(string,optional_precision,optional_scale)
etc.

I know you can write them yourself, but that does very little good to the average user who might want to just do a query without having to write, test, debug, and deploy a pl/sql function. And yes, I can use REGEXP_LIKE and huge honking case statements to achieve the same functionality, but it doesn't make for very clean SQL.

Am I missing something? Are these functions in a package somewhere? This is freaking me out. It seems counter-intuitive that such simple data validation functions wouldn't be built in to an enterprise-class RDBMS.