Proposal: Predicate function

[timonson]

Hi guys, I love your project but I miss a simple predicate function. For example something like this:

export const isValid = (result: Validity): boolean => {
  return result === undefined || (result as OptionalValidity).noContext
};

I am not sure what (result as OptionalValidity).noContext does but I adapted it from assertValid.

It would make it easier to validate values, e.g.:

if (isValid(isEmail("[email protected]"))) {
...
}

Would you mind adding something like this?

Thank you and Happy New Year!