Read only the keys a test allows, and count distinct values

A filter, a fold or a walk's where (a test at the start of its block and a
jump to its end when it fails) that ANDs comparisons of a keyed list's key
with values reading no item gets a range at load (PureRange: a lower bound
GT or GE, an upper LT or LE, EQ both). When it runs, the bounds are found
once and looked up by key, and only the leaves between the two positions
are read: O(log n + k) where it read every item. A filter leaves the items
out of range out anyway, so it always may; a fold or a walk only when the
rest of its test and its value cannot fault (no division, sum or product
that may overflow, key or item that may be missing), since the items it
skips would have run them; a walk's bounds must also read no state, local
or list its block writes, as the where reads them anew for every item.
A bound that faults leaves the test to run for every item, as written.

A fold of kind 5 (distinct) counts the different values its included
items give (-0 as 0), with a set per fold; it runs a leaf at a time and
is never shaped. max, min and first alone fault over no item.

ranges checks, against the same module reading every item, over 60 lists
of up to 400 keyed items and 3,600 views: a count between two bounds, a sum
between a lower and an upper bound with another condition, first equal to
a key, min with the bound on the right, a count whose test may fault (no
range), a filtered table in bounds, 359 walks changing and removing the
items in bounds, and a walk whose body moves its bound (no range).
lane_folds now makes distinct folds too.

0 files changed, 0 insertions, 0 deletions