presto-spi/src/main/java/io/prestosql/spi/type/TypeSignature.java/TypeSignature/functionType
class TypeSignature:    public static TypeSignature functionType(TypeSignature first, TypeSignature... rest)
    {
        List<TypeSignatureParameter> parameters = new ArrayList<>();
        parameters.add(typeParameter(first));

        Arrays.asList(rest).stream()
                .map(TypeSignatureParameter::typeParameter)
                .forEach(parameters::add);

        return new TypeSignature("function", parameters);
    }