[DMS-55] Add Prim.Ret
primitive that acts like var:return
#34
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Problem
Sometimes we want to reference a return variable in predicates. It's not possible because
Prim.forall/Prim.exists
accepts a lambda that shadows the outervar:return
.Example
var:return
in the example refers to the result of the lambda insidePrim.forall
but we want it to be referenced to the result offoo
.Solution
Introduce new primitive
Prim.Ret
with<T>() -> T
type that is translated to$Res
Viper variable.Possible Problems
Since
Prim.Ret
is a regular Motoko's primitive then the user may do some inappropriate actions. For example:We don't restrict such actions. We suppose that
Prim.Ret
would be used only inside assertions. Using it in other places could lead to undefined behavior.