Gergely Buday wrote:
why is it necessary to include the [folder] type in the type of higher
order record functions when it is always inferred?
Isn't it enough to see them as something happening behind the scene?
The [folder] functionality is a convenience added on top of the core Ur
language, which has no support for iteration over records. A key
feature of the Ur type system is that a record is indistinguishable from
any permutation of its fields; in other words, records are inherently
unordered. Building in iteration would break this principle, so
operations that need iteration must be parametrized over [folder] values
that represent orderings. Inference of [folder]s for concrete records
is done in an ad-hoc way, but the core language stays elegant.
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