STOP/SKIP raise StopGlom(), ContinueGlom()?

[kurtbrose]

rather than scanning one level for STOP and SKIP literals, should instead STOP and SKIP have a glomit() which raises StopGlom() and ContinueGlom()?

then, specs for which these make sense can do try/except (StopGlom) within their own glomit()

this gives similar behavior to break and continue keywords in python that they rise to the closest enclosing loop, and it is an error if there is no enclosing loop

[mahmoud]

I think the names'd be like _GlomStop and _GlomContinue, but also, they're basically never going to be raised, right? I imagine that those internal exceptions (as they start to appear) might at most be converted to BadSpec at the top?

[kurtbrose]

yup, 100%

these should have the same semantics as BadSpec -- if they are uncaught that is like having a break outside of a loop in python; syntax error

[mahmoud]

(Note that, for the moment, it's possible for BadSpec to come at runtime. glompilation may change that, but BadSpec may remain a combination runtime/compiletime thing.)

On Tue, Jun 30, 2020 at 12:59 PM Kurt Rose [email protected] wrote:

yup, 100%

these should have the same semantics as BadSpec -- if they are uncaught that is like having a break outside of a loop in python; syntax error

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[kurtbrose]

this may also dovetail into "breadcrumbs" / branching

if we want SKIP and STOP to be handled more centrally by _glom dispatching rather than manually one-by-one in each spec, that might mean having a way to externalize "I'm an iterator; here is my state, here is my current position"

so you could imagine:

def _glom(spec, target, scope):
    result = spec.glomit(target, scope)
    if iterable(result):
        def result_stream():
            while 1:  # assuming underlying StopIteration just bubbles up
                try:
                    yield result.next()
                except GlomContinue:
                    pass
        state = spec.blank()
        try:
            for item in result_stream():
                spec.add(state, item)
        except GlomBreak:
               pass
        return state

[kurtbrose]

or maybe it could just be a helper function for iterable-specs; basically catch Continue "inside the loop", catch Break "outside the loop"

that code pattern is worth abstracting, and by re-using it all over the place we can get broadly compatible / similar behaviors

[kurtbrose]

the most useful pattern of "SKIP as value" is things like Check(..., default=SKIP) or Coalesce(..., default=SKIP)

one alternative to this would be if default used a new ArgSpec, which basically left all atomic values alone, but iterated on list, tuple, dict, set, etc

basically ArgSpec = Fill except it doesn't even call functions