presto-main/src/main/java/io/prestosql/sql/gen/PageFunctionCompiler.java/PageFunctionCompiler/toBlockParameters
class PageFunctionCompiler:    private static List<Parameter> toBlockParameters(List<Integer> inputChannels)
    {
        ImmutableList.Builder<Parameter> parameters = ImmutableList.builder();
        for (int channel : inputChannels) {
            parameters.add(arg("block_" + channel, Block.class));
        }
        return parameters.build();
    }