(l: T.List[str])
return None
Validate language keyword argument.

    Particularly for functions like `add_compiler()`, and `add_*_args()`
Validate language keyword argument.
Validate language keyword argument .
def _language_validator(l: T.List[str]) -> T.Optional[str]:
    """Validate language keyword argument.

    Particularly for functions like `add_compiler()`, and `add_*_args()`
    """
    diff = {a.lower() for a in l}.difference(compilers.all_languages)
    if diff:
        return f'unknown languages: {", ".join(diff)}'
    return None
def _language_validator ( l : T . List [ str ] ) -> T . Optional [ str ] : diff = { a . lower ( ) for a in l } . difference ( compilers . all_languages ) if diff : return f'unknown languages: {", ".join(diff)}' return None