Slice a keyed list: fold and walk over a range of keys

A fold whose kind has PURE_FOLD_SLICED (128), and a walk whose argument
has PURE_EACH_SLICED (bit 0), first take two numbers, a low and a high
key, and run for the items of their list (keyed by a number) whose keys
are from low up to before high, found by key: the range is the program's
meaning, not an optimization, so their blocks may fault (items out of the
slice never run). A fold a leaf at a time now leaves out the lanes of a
leaf outside the items it runs for, and a leaf that would fault runs item
by item over those items alone. Slices are neither shaped nor given
automatic ranges.

ranges now checks a count over a slice whose test divides (a division by
zero failing it only when inside the slice) against a model, the same on
the item-by-item path, and a walk over a slice.

1 files changed, 5 insertions, 0 deletions

diff --git a/core/module.h b/core/module.h
index a93cd69..6132e23 100644
--- a/core/module.h
+++ b/core/module.h
@@ -61,6 +61,11 @@ enum { PURE_MODULE_LOCALS = 64 };
  * (distinct counts the different values, -0 as 0); first gives the index of
  * the first item whose block leaves a non-zero number. */
 typedef enum { PURE_FOLD_COUNT, PURE_FOLD_SUM, PURE_FOLD_MAX, PURE_FOLD_MIN, PURE_FOLD_FIRST, PURE_FOLD_DISTINCT } PureFold;
+/* A slice: a fold whose kind has PURE_FOLD_SLICED, or a walk whose argument
+ * has PURE_EACH_SLICED, first takes two numbers, a low and a high key, and
+ * runs for the items of its list (keyed by a number) whose keys are from
+ * low up to before high, found by key. */
+enum { PURE_FOLD_SLICED = 0x80, PURE_EACH_SLICED = 1 };
 /* TEXT_COMPARE's argument: the relation, in the order of the number
  * comparisons (LT LE GT GE EQ NE); texts order by their bytes. */
 typedef enum { PURE_LESS, PURE_LESS_EQUAL, PURE_GREATER, PURE_GREATER_EQUAL, PURE_EQUAL, PURE_NOT_EQUAL } PureRelation;