[kazinator]

Just the raw formatting of that could be improved, by cuddling up ELSE IF from separate lines.

Aren't there some END tokens missing? Let me put them in:

  IF card is valid DO
    IF card owner is valid DO
      IF request withdrawal DO
        IF authorization code is valid DO
          query for amount
          IF request <= current balance DO
            IF withdrawal <= available cash DO
              vend currency
              debit account
            ELSE
              message
              terminate session
            END
          ELSE
            message
            terminate session
          END
        ELSE
          message
          terminate session
        END
      ELSE
        IF authorization code is valid DO
          query for amount
          accept envelope through hatch
          credit account
        ELSE
          message
          terminate session
        END
    ELSE
      eat card
    END
  ELSE
    message
  END

Okay, now:

  IF card is valid DO
    IF card owner is valid DO
      IF request withdrawal DO
        IF authorization code is valid DO
          query for amount
          IF request <= current balance DO
            IF withdrawal <= available cash DO
              vend currency
              debit account
            ELSE
              message
              terminate session
            END
          ELSE
            message
            terminate session
          END
        ELSE
          message
          terminate session
        END
      ELSE IF authorization code is valid DO
        query for amount
        accept envelope through hatch
        credit account
      ELSE
        message
        terminate session
      END
    ELSE
      eat card
    END
  ELSE
    message
  END

Okay, just one ELSE IF; not much opportunity for that.

[kazinator]

On that topic, I did a somewhat weird thing in C yesterday. I took code like this:

  for (;;) {
    /* original big loop */
  }

and turned it into this:

  if (compatibility_with_old_version) for(;;) {
    /* original big loop: same indentation level! */
  } else for (;;) {
    /* rewritten new loop */
  }
 

I.e.

  if (...) for (...) {

  } else for (...) {

  }

Works for me.