Edward Z. Yang wrote:
Excerpts from Edward Z. Yang's message of Sat Apr 14 19:29:32 -0400 2012:
This particular permutation gives me:
/home/ezyang/Dev/logitext/meta/json.ur:300:55-300:69: Can't resolve type
class instance
Class constraint: Top.folder[[Type]] rest
and I don't know how to spell the implicit arguments correctly or what
folder I should be giving it (it's /almost/ 'fl' except that the
entries in front need to be lopped off). Is there a version of fold which
also gives me folders?
Here's an idea: fold once to get a record of folders, and fold again
with that. But maybe the unification won't be clever enough.
Oh, yeah; I didn't think of this issue. It's probably easier to stop
using [Variant.weaken]; instead, you can choose your accumulator type to
be polymorphic in an extra type-level record to concatenate into the
index to [variant]. (This general pattern appears a few times in
variant.ur, including in the first function definition.)
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