How to check if an array contains a value?

[msarrel]

What is the allowable syntax for conditional expressions?

I have to test if a field is equal to any one of 63 values. The only way I can think to do this is the following, where x1, x2, x3 etc. are integers and a is the field id.

if: a==x1 or a==x2 or a==x3 or ... or a==x63

There has to be a shorter way. Maybe something like list inclusion?

if: a in [x1, x2, x3, ..., x63]

[KOLANICH]

There is no shorter way. But +1 for set matching. And -1 for the syntax proposed. IMHO we should move to the direction of dict-based syntax for expressions.

[msarrel]

Thanks for the answer, even if it isn't what I had hoped for...

[generalmimon]

@msarrel:

There has to be a shorter way. Maybe something like list inclusion?

As @KOLANICH points out, there is no dedicated built-in way in the expression language other than the or chain like in your first sninpet. Probably it makes sense to add it eventually, but it's more of a low priority issue.

If we will ever implement this feature, it would be nice to make it work for ranges (which don't exist in Kaitai Struct yet, but were proposed in #130) and perhaps enums (#518), too.

Currently we have only valid/any-of as a part of #435 (but that's only for validation, i.e. the parsing ends with a validation error if the parsed value didn't match), but it's basically a syntactic sugar for v == 1 or v == 2 or ... as well.

However, with a bit of ingenuity, you can actually implement the list inclusion operation yourself, but I'll let you decide for yourself whether this counts as a "shorter" way:

seq:
  - id: match_steps
    type: 'match_step(known_values[_index], _index != 0 ? match_steps[_index - 1].is_known : false)'
    repeat: expr
    repeat-expr: known_values.size
instances:
  a:
    value: 42
  known_values:
    value: '[1, 2, 42, 46]'
  is_a_in_known_values:
    value: match_steps.last.is_known
types:
  match_step:
    -webide-representation: '{is_known}'
    params:
      - id: cur_known_value
        type: s4
      - id: prev_is_known
        type: bool
    instances:
      is_known:
        value: prev_is_known or _parent.a == cur_known_value

Result (see https://ide.kaitai.io/):

├─ matchSteps
│  ├─ 0 [MatchStep]: false
│  ├─ 1 [MatchStep]: false
│  ├─ 2 [MatchStep]: true
│  └─ 3 [MatchStep]: true
├─ a = 42
├─ knownValues
│  ├─ 0 = 1
│  ├─ 1 = 2
│  ├─ 2 = 42
│  └─ 3 = 46
└─ isAInKnownValues = true