PTC and "SHOULD" vs "MUST"

David Herman dherman at mozilla.com
Wed Jun 1 17:55:22 PDT 2011


Agreed. Should be "must."

Dave

On Jun 1, 2011, at 3:42 PM, Brendan Eich wrote:

> Thanks for catching this, it goes back to http://wiki.ecmascript.org/doku.php?id=strawman:proper_tail_calls&rev=1273414092 (first rev). Cc'ing Mark. I bet it is just a thinko for MUST and we can fix it quickly.
> 
> /be
> 
> On Jun 1, 2011, at 3:36 PM, Peter Michaux wrote:
> 
>> http://wiki.ecmascript.org/doku.php?id=harmony:proper_tail_calls
>> 
>> I notice that in the proper tail calls wiki page that a compliant
>> interpreter "SHOULD implement a call in proper tail position as a
>> PTC." In order for a programmer to use proper tail calls for
>> arbitrarily deep recursion, the programmer needs a guarantee that the
>> interpreter will use proper tail calls. This would mean the "SHOULD"
>> needs to be a "MUST". Otherwise what does the proper tail calls
>> proposal gain the programmer?
>> 
>> For example, R5RS has much stronger language compared with "SHOULD"
>> about Scheme using proper tail calls.
>> 
>> "Implementations of Scheme are required to be properly tail recursive."
>> 
>> With that language the programmer using Scheme can then depend on that feature.
>> 
>> Peter
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> 
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