set vars with another vars

[knsh14]

I try to make vars like below

version: 3

vars:
  FOO: foo
  BAR: bar
  FOOBAR: {{.FOO}}{{.BAR}}

tasks:
  echo:
    cmds:
      - echo {{.FOOBAR}}

then executed task echo then failed and message is below

yaml: line 5: did not find expected key

so maybe setting vars.FOOBAR with another var is wrong.
I want to generate var with other vars like versions. so will this be fixed?

[knsh14]

ah I missed examples in repo...
https://github.com/go-task/task/blob/master/testdata/vars/v3/Taskfile.yml

this helped me!