presto-spi/src/main/java/io/prestosql/spi/type/VarcharType.java/VarcharType/getParametrizedVarcharSignature
class VarcharType:    public static TypeSignature getParametrizedVarcharSignature(String param)
    {
        return new TypeSignature(StandardTypes.VARCHAR, TypeSignatureParameter.typeVariable(param));
    }