feat(dcons): add ISeqable impl (seq()) & tests

thi-ng · Nov 15, 2019 · 1cfb02a · 1cfb02a
1 parent d94df57
commit 1cfb02a
Show file tree

Hide file tree

Showing 2 changed files with 50 additions and 3 deletions.
diff --git a/packages/dcons/src/index.ts b/packages/dcons/src/index.ts
@@ -8,6 +8,8 @@ import {
     IEquiv,
     ILength,
     IRelease,
+    ISeq,
+    ISeqable,
     IStack,
     Predicate
 } from "@thi.ng/api";
@@ -32,6 +34,7 @@ export class DCons<T>
         ILength,
         IReducible<any, T>,
         IRelease,
+        ISeqable<T>,
         IStack<T, T, DCons<T>> {
     head: ConsCell<T> | undefined;
     tail: ConsCell<T> | undefined;
@@ -124,12 +127,29 @@ export class DCons<T>
         }
     }
 
+    /** {@inheritDoc @thi.ng/api#ISeqable.seq} */
+    seq(start = 0, end = this.length) {
+        if (start >= end || start < 0) return;
+        let cell = this.nthCell(start);
+        const last = this.nthCell(end - 1);
+        const $seq = (cell: ConsCell<T>): ISeq<T> => ({
+            first() {
+                return cell.value;
+            },
+            next() {
+                return cell !== last && cell.next ? $seq(cell.next) : undefined;
+            }
+        });
+        return cell ? $seq(cell) : undefined;
+    }
+
     *cycle() {
         while (true) {
             yield* this;
         }
     }
 
+    /** {@inheritDoc @thi.ng/transducers#IReducible.$reduce} */
     $reduce(rfn: ReductionFn<any, T>, acc: any) {
         let cell = this.head;
         while (cell && !isReduced(acc)) {

diff --git a/packages/dcons/test/index.ts b/packages/dcons/test/index.ts
@@ -1,7 +1,6 @@
 import * as assert from "assert";
 import { DCons } from "../src/index";
 
-
 describe("DCons", () => {
     let a: DCons<any>, src: number[];
     beforeEach(() => {
@@ -23,7 +22,35 @@ describe("DCons", () => {
         assert.deepEqual([...a], src);
     });
 
-    it("works as stack");
+    it("is seqable", () => {
+        assert.equal(a.seq()!.first(), 1);
+        // prettier-ignore
+        assert.equal(a.seq()!.next()!.first(), 2);
+        // prettier-ignore
+        assert.equal(a.seq(3)!.first(), 4);
+        // prettier-ignore
+        assert.equal(a.seq(3)!.next()!.first(), 5);
+        // prettier-ignore
+        assert.equal(a.seq(3)!.next()!.next(), undefined);
+        assert.equal(a.seq(2, 2), undefined);
+        assert.equal(a.seq(2, 3)!.first(), 3);
+        assert.equal(a.seq(2, 3)!.next(), undefined);
+    });
+
+    it("works as stack", () => {
+        assert.equal(a.push(10).pop(), 10);
+        assert.equal(a.pop(), 5);
+        a = new DCons();
+        assert.equal(a.pop(), undefined);
+    });
 
-    it("works as queue");
+    it("works as queue", () => {
+        assert.equal(a.push(10).drop(), 1);
+        assert.equal(a.drop(), 2);
+        assert.equal(a.drop(), 3);
+        assert.equal(a.drop(), 4);
+        assert.equal(a.drop(), 5);
+        assert.equal(a.drop(), 10);
+        assert.equal(a.drop(), undefined);
+    });
 });