create statically typed variant of versioning lib

lib/versioning/static/merge.js

@@ -0,0 +1,69 @@
+import { emptySet, add, length, forEach, has, remove } from "../../structures/set.js";
+import { getDepth, Slot } 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);
+  }
+};
+
+// returns
+//  {slotA} if slotA is younger
+//  {slotB} if slotB is younger
+//  {slotA, slotB} if they are concurrent (conflicting)
+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 result = slots;
+  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)) {
+            result = remove(result)(slotB);
+          }
+        }
+      }
+    });
+  });
+  return result;
+};
+
+const mkType = makeTypeParser({
+  extraBracketOperators: [
+    [':=', ['=:', Slot]],
+  ],
+});
+
+export const ModuleStaticMerge = [
+  ["merge" , newDynamic(merge)(mkType(":=a=: -> :=a=: -> {:=a=:}"))],
+  ["mergeN", newDynamic(merge)(mkType("{:=a=:} -> {:=a=:}"       ))],
+];