Variables - immediate evaluation while using a variable?

[FredrikAir]

Has someone any idea how to solve my problem?
I want to use the immediate evaluation on the variable clothes_sleeves, but it will not work. (last line)

clothes_top:
  - t-shirt
  - buttoned-shirt
t-shirt:
    sleeves:
      - long sleeves
      - short sleeves
buttoned-shirt:
    sleeves:
      - long sleeves
      - short sleeves
      - rolled up sleeves
      - unbuttoned sleeves

${clothes_top=!{__clothes_top__}}
${clothes_sleeves=!{__${clothes_top}/sleeves__}}

This gives an error.

When I use the non-immediate evaluation (without the exclamation mark), it works.
But then the result will vary as the script continues to use the variable in other places.

clothes_top:
  - t-shirt
  - buttoned-shirt
t-shirt:
    sleeves:
      - long sleeves
      - short sleeves
buttoned-shirt:
    sleeves:
      - long sleeves
      - short sleeves
      - rolled up sleeves
      - unbuttoned sleeves

${clothes_top=!{__clothes_top__}}
${clothes_sleeves={__${clothes_top}/sleeves__}}