call role with arg, set_fact

main.yml

# /etc/ansible/roles/tmp/tasks/main.yml
---
- name: do something with passed var
  debug: var=myothervar

- name: do something with set_fact var
  debug: var=myvar

output

PLAY [all] ********************************************************************

TASK: [register a fact] *******************************************************
ok: [localhost]

PLAY [all] ********************************************************************

TASK: [tmp | do something with passed var] ************************************
ok: [localhost] => {
    "item": "",
    "myothervar": [
        "one",
        2,
        "three"
    ]
}

TASK: [tmp | do something with set_fact var] **********************************
ok: [localhost] => {
    "item": "",
    "myvar": [
        "one",
        2,
        "three"
    ]
}

PLAY RECAP ********************************************************************
localhost                  : ok=3    changed=0    unreachable=0    failed=0

tmp.yml

# /etc/ansible/tmp.yml
---
- hosts: all
  gather_facts: no
  tasks:
    - name: register a fact
      set_fact: myvar="['one',2,'three']"

- hosts: all
  gather_facts: no
  roles:
    - { role: tmp, myothervar: "{{ myvar }}" }