Does Expr have Control flow

[Pat3ickI]

Hey, good day am trying to integrate this into a project as a middleware for the project, I predicted the script is gonna get a little complex, is there a way to have if statements or if-else, I can’t find any documentation or issues about this.
Thanks

[daenney]

As far as I know, Expr only has the ternary statement:

valueA != valueB ? do-if-true : do-if-false

It's in the Operators.

[antonmedv]

Yeap. But I do want to implement if statements as well.

[ctcx]

If it could support control flow and custom functions, that would be great.

[antonmedv]

Custom functions already supported.

[phuslu]

maybe we can implement a simple "pattern matching" first?

match a {
    1 -> "foo"
    2 -> "bar"
    default -> "none"
}

or

switch {
case <condition 1> -> "foo"
case <condition 2> -> "bar"
default -> "none"
}

something like aboves is really help

[phuslu]

BTW: currently I use go template + sprig for implement my business logic, it's too heavy and a bit slow than expr. The blocker of my expr migration is if statement or pattern matching.

[antonmedv]

So what king of the problem are you trying to solve? Please, more context.

[phuslu]

Here an example of my side project, https://github.com/phuslu/liner/blob/master/example.yaml#L47-L66 , please the "policy" and "dialer" field.

[phuslu]

k8s helm also use same idiom, see https://helm.sh/docs/chart_template_guide/control_structures/

[pelletier197]

Would greatly benefit control flow as well. Either switch case or if/else are good options for my use-cases. I can work around with ternary however, just less practical.

[rchougule]

@antonmedv Any plans on having if-else in near future? It's easier for business folks as well to use

[antonmedv]

Yes, we are planning to implement if-else in near future. I guess this will be a new feature after current release.

[xiaoas]

I'm facing a scenario where if-else proves very helpful, consider this script:

if input1 != "" {
  return input1
}
b := calculateB(input2);
c := calculateC();
return getResult(b, c);

To do this in go expr, I'm currently planning to write this:

let b = input1 == "" ? calculateB(input2) : nil;
let c = input1 == "" ? calculateC() : nil;
input1 != "" ? input1 : getResult(b, c)

It would be so much nicer if the expression language has a "return" keyword, or a rust-like if-else expression:

if input1 != "" {
  input1
} else {
  let b = calculateB(input2);
  let c = calculateC();
  getResult(b, c)
}

I would say this is easier to read.

[antonmedv]

True! This is why we are working on it. ping @OlgaNovg ;)

[pagrus7]

#736
Looks like this pull request has been open few months ago. Is there a path forward?
(I'm evaluating expr for a use case which needs control flow)

[antonmedv]

Yes! @OlgaNovg is also waiting long time already)

[pagrus7]

Hey folks - excited that this is now merged! Is there a timeline for the next release?

[antonmedv]

Soon! I have to fix a few issues before. And i want to add support for sequence of expressions.

[antonmedv]

Now Expr has control flows!

let foo = if bar > 0 { 
    true
} else {
    false
}

[sonnysideup]

where is the documented?

[Ariyn]

you can read this in 1.17.0 release note.

Very small and short, but there is a document too. (Maybe no one made a detailed document PR yet)