How to use [signal]

The reference page of signal has its arguments, constraints and declaration.

Invokes a previously created dynamic slot. Assuming you have created the foo slot from the create slot example, you can invoke the slot using the following Hyperlambda.

signal:foo

After evaluating the above Hyperlambda, the [signal] node will end up having a value of “57”.

Notice - This slot obeys by the rules of [whitelist] invocations from magic.lambda, allowing you to declare a list of dynamic slots, which are exclusively allowed to be invoked temporarily inside of an invocation to whitelist, allowing you to restrict some piece of potentially unsafe code to only signal a pre-defined list of dynamically created slots. Below is an example.

slots.create:foo1
   return-value:Safe

slots.create:foo2
   return-value:Unsafe

whitelist

   vocabulary
      signal
      signal:foo1

   .lambda

      // Assuming you have a [foo1] slot created, this will work
      signal:foo1

      // This will throw, since [foo2] is not whitelisted
      signal:foo2

Basically, only the slots declared in the above [vocabulary] will be allowed to be invoked inside of the above [.lambda] object. You must have your dynamic slots declared as signal:slot-name, such as the above illustrates. And in order to signal dynamic slots at all, you’ll need to (obviously) whitelist [signal] itself, as illustrated in the above code. Read more about [whitelist] in the magic.lambda project. Inside your slots though any [whitelist] invocations will simply be ignored, allowing you to whitelist a single dynamic slot, for then to ignore what the slot itself is doing internally. This might create security issues for you if you have dynamically created slots that for some reasons execute lambda object supplied to them. Hence as a general rule of thumb, you should avoid whitelisting slots that executes lambda objects supplied to them. The same is true for Hyperlambda files executed with [execute-file] or [io.file.execute], which you can pin in a whitelist by path - see magic.lambda.io.