The combine operator can be used to produce the Cartesian product:

sample_bams = Channel.fromPath( './path/to/bams/*.bam' )
intervals = Channel.of( '1:10000-20000', '5:55555-77777' )

sample_bams
    .combine(intervals)
    .set { combined_inputs }


process test {

    echo true

    input:
    tuple path(bam), val(interval) from combined_inputs

    """
    echo -n "${interval} ${bam}"
    """
}

The combine operator can be used to produce the Cartesian product:

sample_bams = Channel.fromPath( './path/to/bams/*.bam' )
intervals = Channel.of( '1:10000-20000', '5:55555-77777' )

sample_bams
    .combine(intervals)
    .set { combined_inputs }


process test {

    echo true

    input:
    tuple path(bam), val(interval) from combined_inputs

    """
    echo -n "${interval} ${bam}"
    """
}

Regarding the related query: Correct. The from and into 'bind' declarations can be omitted