How to raise an exception from a template?

[spip]

I'm using Nim type system and templates to build a table of allowed types in a 
DSL language, like the following:
    
    
    template final_sort2(v: bool): typedesc =
      AST_bool
    template final_sort2(v: int): typedesc =
      AST_int
    ...
    template final_sort2(v: typed): typedesc =
      {.line: instantiationInfo().}:
        raise newException(Exception, "Incompatible type: " & $v)
    
    
    Run

How can I have the compiler raise the exception when the last template is 
selected?

The code works without that last template, but the error message and the stack 
trace reported by the compiler does not help the developer understand the 
reason of the problem.
    
    
    Error: in expression 'final_sort(b)(ite`gensym19185006)': identifier 
expected, but found 'final_sort(b)'
    
    
    Run

I would rather have a specific message reported when I can.