Can't emit an array of obligations formed from an array of values

[frbrkoala]

Bug Report 🐛

I need to emit multiple events based on the list of vendors, specified in my contract.

Here is how I envision that:

My grammar.tem.md:

[...]
{{#ulist vendors}}
{{businessName}}
{{/ulist}}
[...]

My model.cto:

event VendorNotification {
        o String code
        o String description
        o Vendor vendor
}

transaction NotifyVendorsReq extends Request {
  o String detectionCode
  o String description
}

transaction NotifyVendorsRes extends Response {
  o String output
}

participant Vendor identified by businessName {
  o String businessName
}
asset MyContract extends Contract {
  o Vendor[] vendors
}

And logic.ergo:

contract MyContractLogic over MyContract state State {
  
  //Iterate through an array of vendors and emit an event for each of them
  clause notifyVendors(request : NotifyVendorsReq) : NotifyVendorsRes emits VendorNotification[] {

    emit foreach vendor in contract.vendors
    return VendorNotification {
        code: request.notificationCode,
        description: request.description,
        vendor: vendor
     };
    
    return NotifyVendorsRes{ output: "Received " ++ request.notificationCode ++ " " ++ request.description ++ " and sent notification to vendors " ++ toString(contract.vendors) }
  }
}

cicero trigger throws “ERROR: Cannot read property ‘$coll’ of undefined”

Expected Behavior

The contract should emit an array of events

Current Behavior

Throws an error: “ERROR: Cannot read property ‘$coll’ of undefined”

Possible Solution

Would be good to make emit function compatible with an array of events.

Steps to Reproduce

Please see the bug report section.

Context (Environment)

Desktop

• OS: macOS
• Browser: NodeJS v10.18.1
• Version: "cicero": "^0.22.1"

Detailed Description

The emit function can receive an array of events and emit them one-by-one to address the situation when multiple events need to be emitted in one go.

Possible Implementation

[jeromesimeon]

@frbrkoala Thanks for the bug report / feature request.

Just a quick update:

1. I was able to reproduce the issue. See the archive attached based on your example.
   vendors@0.1.0.zip

2. The $coll exception is a runtime error which comes from an inconsistency between the Ergo type checker and the compiler. I think the intended behavior is for the suggested logic to fail type checking (with an error that the emit should be a singleton object).

3. This is a perfectly valid and useful requirement imho. I think there might be two ways to support this. First being your suggestion i.e., allow emit to take either a single item or an array (which would make it polymorphic). Second might be to keep emit over single items but generalize where emit is allowed and notably allow it use inside foreach. This would look something as follows (both options probably need work):

contract MyContractLogic over MyContract state State {
  
  //Iterate through an array of vendors and emit an event for each of them
  clause notifyVendors(request : NotifyVendorsReq) : NotifyVendorsRes emits VendorNotification[] {

    foreach vendor in contract.vendors
    return
       emit  VendorNotification {
          code: request.notificationCode,
          description: request.description,
          vendor: vendor
       };
    
    return NotifyVendorsRes{ output: "Received " ++ request.notificationCode ++ " " ++ request.description ++ " and sent notification to vendors " ++ toString(contract.vendors) }
  }
}