PTC and "SHOULD" vs "MUST"

Brendan Eich brendan at
Wed Jun 1 15:42:08 PDT 2011

Thanks for catching this, it goes back to (first rev). Cc'ing Mark. I bet it is just a thinko for MUST and we can fix it quickly.


On Jun 1, 2011, at 3:36 PM, Peter Michaux wrote:

> 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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