progress with versioning

lib/versioning/merge.js

@@ -0,0 +1,73 @@
+import { emptySet, add, length, forEach, union, has } from "../structures/set.js";
+import { getDepth, Slot, Value, Write } from "./value_slot.js";
+import { compareSlot } from "./compare.js";
+import { makeTypeParser } from "../parser/type_parser.js";
+import { newDynamic } from "../primitives/dynamic.js";
+
+const emptySetOfSlots = emptySet(compareSlot);
+
+export const findLCA = slotA => slotB => {
+  if (compareSlot(slotA)(slotB) === 0) {
+    return slotA;
+  }
+  if (getDepth(slotA) > getDepth(slotB)) {
+    // we can assume that slotA.variant === "write"
+    return findLCA(slotA.value.slot)(slotB);
+  }
+  else {
+    // we can assume that slotB.variant === "write"
+    return findLCA(slotA)(slotB.value.slot);
+  }
+};
+
+export const merge = slotA => slotB => {
+  const lca = findLCA(slotA)(slotB);
+  if (compareSlot(lca)(slotA) === 0) {
+    return add(emptySetOfSlots)(slotB);
+  }
+  if (compareSlot(lca)(slotB) === 0) {
+    return add(emptySetOfSlots)(slotA);
+  }
+  const setWithA = add(emptySetOfSlots)(slotA);
+  const setWithAandB = add(setWithA)(slotB);
+  return setWithAandB;
+};
+
+export const mergeN = slots => {
+  let toDelete = emptySetOfSlots;
+  forEach(slots)(slotA => {
+    forEach(slots)(slotB => {
+      // compare all non-identical pairs
+      if (compareSlot(slotA)(slotB) !== 0) {
+        const m = merge(slotA)(slotB);
+        if (length(m) === 1) {
+          // if in the pair, one is an ancestor of the other,
+          // only keep the other
+          if (has(m)(slotA)) {
+            toDelete = add(toDelete)(slotB);
+          }
+        }
+      }
+    });
+  });
+  let result = emptySetOfSlots;
+  forEach(slots)(slot => {
+    if (!has(toDelete)(slot)) {
+      result = add(result)(slot);
+    }
+  })
+  return result;
+};
+
+const mkType = makeTypeParser({
+  extraPrimitives: [
+    ["Value", Value],
+    ["Slot" , Slot ],
+    ["Write", Write],
+  ],
+});
+
+export const ModuleMerge = [
+  ["merge" , newDynamic(merge)(mkType("Slot -> Slot -> {Slot}"))],
+  ["mergeN", newDynamic(merge)(mkType("{Slot} -> {Slot}"      ))],
+];