DMN17 — Built-in functions returning abstract types

The DMN specification contains several built-in functions with abstract return types. For example, the semantics for

duration(input) + time("12:00:00")

cannot be checked before the execution, as only days and time durations are allowed in this context.

The same is true for expressions such as

context(input).name
context put({x:1}, key, value).y

as the context() and context put() functions return an unknown context.

Adding support for explicit conversions will address these issues. For example,

(duration(input) as days and time duration) + time("12:00:00")
(context(input) as context<name: string, age: number>).name

Add 'as <type>' operator to FEEL

Add an operator to explicitly declare expected types or trigger an error