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Ticket 35: dynamically scoped values

2010-11-15 09:51:41
WG1 - Core
2010-02-23 17:09:13

Do we provide any values with dynamic scope, such as SRFI-39 parameters? How do they interact with call/cc and/or threads?

SRFI 39 parameters are supported (according to the documentation) by PLT, Gauche, Gambit, Chicken, Guile, Kawa, SISC, Chibi, IronScheme, Ikarus, Larceny, Mosh, STKlos.

MIT, Bigloo, Scheme48/scsh, Chez, SCM, Ypsilon, s7, SigScheme, SXM, Pocket, stk, Sizzle, Scheme 9 do not support them.

Call/cc should not interact with dynamic parameters.

I don't believe that WG1 should standardize threads, so I don't think we have to decide about them. The SRFI notes three possible ways to interact: reset all parameters in each new thread, copy the current state of all parameters to new threads, share parameters with new threads. In all cases, parameters in new threads are in the ground (un-parameterized) state.

As to why we should standardize them at all, it's because if portable code wants to expose parameters, it will have to provide the parameter procedures itself in a thread-unsafe way, which will combine badly on threaded systems with any existing parameter procedures.


Duplicate of #69.