Runtime type checks and type inference in Unicon
The Unicon language handles types a lot differently than the Jzero type system described in this chapter. In Unicon, types are not associated with declarations but with actual values. The Unicon virtual machine code generator does not place type information in symbol tables or do compile-time type checking. Instead, types are represented explicitly at runtime and checked everywhere before a value is used. Explicitly representing type information at runtime is common in interpreted and object-oriented languages, and optional in some semi-object-oriented languages such as C++.
Consider the write() Unicon function. Every argument to write() that isn't a file specifying where to write to must be a string, or be able to be converted into a string. In the Unicon virtual machine, the type information is created and checked at runtime as needed. The pseudocode for the Unicon write() function looks like this:
for (n = 0; n < nargs...