restructure code a bit, add comparison functions for primitive types and composed types (needed to put values in sets)

compare/structures.js

@@ -0,0 +1,58 @@
+import { compareNumbers } from "./primitives.js"
+import { length as lengthLs } from "../structures/list.js";
+import { read, length as lengthSet } from "../structures/set.js";
+import { constructorProduct, getLeft, getRight } from "../structures/product.js";
+import { match } from "../structures/sum.js";
+
+// (a -> a -> Int) -> [a] -> [a] -> Int
+export const compareLists = compareElems => x => y => {
+  return compareNumbers(lengthLs(x))(lengthLs(y))
+    || (() => {
+      for (let i=0; i<lengthLs(x); i++) {
+        const elemCmp = compareElems(get(x)(i))(get(y)(i));
+        if (elemCmp !== 0) {
+          return elemCmp;
+        }
+      }
+      return 0;
+    })();
+};
+
+// (a -> a -> Int) -> (b -> b -> Int) -> (a, b) -> (a, b) -> Int
+export const compareProducts = compareLeft => compareRight => x => y => {
+  return compareLeft (getLeft (x))(getLeft (y))
+      || compareRight(getRight(x))(getRight(y));
+};
+
+// (a -> a -> Int) -> (b -> b -> Int) -> (a | b) -> (a | b) -> Int
+export const compareSums = compareLeft => compareRight => x => y => {
+  return match(x)(constructorProduct
+    (leftValueX => match(y)(constructorProduct
+      (leftValueY => compareLeft(leftValueX)(leftValueY))
+      ((rightValueY) => -1) // x is 'left' and y is 'right' => x < y
+    ))
+    (rightValueX => match(y)(constructorProduct
+      (leftValueY => 1) // x is 'right' and y is 'left' => x > y
+      (rightValueY => compareRight(rightValueX)(rightValueY))
+    ))
+  );
+};
+
+// (a -> a -> Int) -> {a} -> {a} -> Int
+export const compareSets = compareElems => x => y => {
+  return compareNumbers(lengthSet(x))(lengthSet(y))
+    || (() => {
+      // sets have same size -> iterate over both sets and compare their elements pairwise
+      // because of the underlying red-black tree, iteration happens in ordered fashion
+      const iterate = iterX => iterY =>
+        read(iterX)
+        (keyX => nextX =>
+          read(iterY)
+            // we could also use the comparison function that is embedded in the set object,
+            // but to be consistent with the other comparison-functions, we don't.
+            (keyY => nextY => compareElems(keyX)(keyY) || iterate(nextX)(nextY))
+            (0)) // end of set y (we'll never get here because sets are same size)
+        (0) // end of set x;
+      iterate(first(x))(first(y));
+    })();
+};