public function validate($value)
    {
        return is_string($value) ? Ok::unit() : Error::unit([ Error::NON_STRING ]);
    }
public function validate($value)
    {
        return is_string($value) ? Ok::unit() : Error::unit([ Error::NON_STRING ]);
    }
public function validate ( $ value ) { return is_string ( $ value ) ? Ok :: unit ( ) : Error :: unit ( [ Error :: NON_STRING ] ) ; }
Tells if a given value is a valid string.

@param mixed $value

@return ResultInterface Returns Ok if the value is valid, otherwise an Error is returned.
Tells if a given value is a valid string .