Python from Wise Guy's Viewpoint

[Neelakantan Krishnaswami]

In article <boqboc$4p2$1 at f1node01.rhrz.uni-bonn.de>, Pascal Costanza wrote:
> Fergus Henderson wrote:
> 
>> Suppose the original ML program defines the following functions
>> 
>> 	foo : int -> int
>> 	bar : string -> string
>> 	...
>> 
>> We can add dynamic typing like this:
>> 
>> 	datatype Generic = Int of int
>> 			 | String of string
>> 			 | Atom of string
>> 			 | Cons Generic Generic
>> 			 | Apply Generic Generic
>> 			 | ...
>                             ^^^
> How many do you need of those, especially when you want to allow that 
> type to be extended in the running program?

Two more.

  datatype generic = ...
                   | Class of generic ref
                   | Object of generic array ref

Then you can write a typeof function that looks at tags to decide what
to do.

This shouldn't be that hard to see: an implementation of Scheme or
Lisp doesn't require an infinite family of tags in the lower-level
implementation.


-- 
Neel Krishnaswami
neelk at cs.cmu.edu