<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def rnaseq_variant_calling(samples, run_parallel):
 """ run RNA-seq variant calling using GATK """

    samples = run_parallel("run_rnaseq_variant_calling", samples)
    variantcaller = dd.get_variantcaller(to_single_data(samples[0]))
    if variantcaller and ("gatk-haplotype" in variantcaller):
        out = []
        for d in joint.square_off(samples, run_parallel):
            out.extend([[to_single_data(xs)] for xs in multi.split_variants_by_sample(to_single_data(d))])
        samples = out
    if variantcaller:
        samples = run_parallel("run_rnaseq_ann_filter", samples)
    if variantcaller and ("gatk-haplotype" in variantcaller):
        out = []
        for data in (to_single_data(xs) for xs in samples):
            if "variants" not in data:
                data["variants"] = []
            data["variants"].append({"variantcaller": "gatk-haplotype", "vcf": data["vrn_file_orig"],
                                     "population": {"vcf": data["vrn_file"]}})
            data["vrn_file"] = data.pop("vrn_file_orig")
            out.append([data])
        samples = out
    return samples