Merging sequences


When multiple sequences are merged into one sequence, the new sequence takes an element from each input sequence in turn. For example, if we merge
{ 1 2 3 }

and
{ "a" "b" "c" }

we get:
{ 1 "a" 2 "b" 3 "c" }

.
merge ( seqs -- seq )

2merge ( seq1 seq2 -- seq )

3merge ( seq1 seq2 seq3 -- seq )

<merged> ( seqs -- merged )

<2merged> ( seq1 seq2 -- merged )

<3merged> ( seq1 seq2 seq3 -- merged )