Discussion Towards: Incremental Coding/ Native Query Language in Julia

General Usage
2

Variables indeed can have declared types without assigned values. Access without a value errors, and so does assignment of values that can’t be converted to the declared type. Note that the local/global keywords are necessary because x::Int already means type assertion of the instance assigned to a variable.

julia> module TypedDemo
         global x::Int
         function foo(z)
           local y::Int
           y = z
         end
       end
Main.TypedDemo

julia> TypedDemo.x
ERROR: UndefVarError: `x` not defined in `Main.TypedDemo`
Suggestion: add an appropriate import or assignment. This global was declared but not assigned.
Stacktrace:
...

julia> TypedDemo.x = "one"
ERROR: MethodError: Cannot `convert` an object of type String to an object of type Int64
...

julia> TypedDemo.foo("one")
ERROR: MethodError: Cannot `convert` an object of type String to an object of type Int64
...

That alone doesn’t come close to the things discussed here, but maybe it can be useful.