If you have function calls without type information, anything can happen, a function call could result in your neighbor's pool being drained, and your bank balance being sent to Belize.
In Pascal, you have to have a type before you can declare a variable. This little inconvenience saves you from an entire class of errors.
If I'm going to import a random file from the internet, I have to be sure of the type of data in it before I'm going to touch it with a 10 foot pole (or barge pole in Britain).
I had no idea people got so foolish.
Back to your idea, of course there should be type information, either as a separate file, or at the head of the file.
In Pascal, I'd have the import routine check it against the RTTI (run time type information) of the local native structure as part of the import, and throw errors if there were problems. On export, the RTTI could create the type header file/section of JSON.
