Missing comma not reported as Syntax Error

This line appears in t007_types+objects_test:
```
        assertType (Function3⟦Unknown, Unknown, Unknown Number⟧) describes {a, b, c → 1}
```

There is a comma missing between `Unknown` and `Number` in the type arguments to `Function3`.  This is a syntax error (I believe), but is not reported as such by the parser.