1 files changed, 68 insertions, 0 deletions
diff --git a/common.js b/common.js
new file mode 100644
index 0000000..b8e8464
--- /dev/null
+++ b/common.js
@@ -0,0 +1,68 @@
+/* lambda calculus */
+
+const allHashes = {};
+const hash = (s) => {
+  let h = 0;
+  for (let i = 0; i < s.length; i++) {
+    const chr = s.charCodeAt(i);
+    h = (h << 5) - h + chr;
+    h |= 0;
+  }
+  while (h in allHashes && allHashes[h] !== s) h += 1;
+  allHashes[h] = s;
+  return h;
+};
+
+const abs = (body) => {
+  if (body === null) return null;
+  const t = { type: "abs", body };
+  t.hash = hash("abs" + body.hash);
+  return t;
+};
+
+const app = (left) => (right) => {
+  if (left === null || right === null) return null;
+  const t = { type: "app", left, right };
+  t.hash = hash("app" + left.hash + right.hash);
+  return t;
+};
+
+const idx = (idx) => {
+  if (idx === null) return null;
+  const t = { type: "idx", idx };
+  t.hash = hash("idx" + idx);
+  return t;
+};
+
+const def = (name) => {
+  const t = { type: "def", name };
+  t.hash = hash("def" + name);
+  return t;
+};
+
+/* lambda screen */
+
+const WHITE = 0;
+const BLACK = 1;
+const UNKNOWN = 2;
+
+// [[1]]=w, [[0]]=b, other=g
+const toColor = (t) => {
+  if (t.type === "abs" && t.body.type === "abs" && t.body.body.type === "idx")
+    return t.body.body.idx === 1
+      ? WHITE
+      : t.body.body.idx === 0
+        ? BLACK
+        : UNKNOWN;
+  return UNKNOWN;
+};
+
+// [((((0 tl) tr) bl) br)]
+const seemsScreeny = (t) =>
+  t.type === "abs" &&
+  t.body.type === "app" &&
+  t.body.left.type === "app" &&
+  t.body.left.left.type === "app" &&
+  t.body.left.left.left.type === "app" &&
+  t.body.left.left.left.left.type === "idx" &&
+  t.body.left.left.left.left.idx === 0;