t.nestLeft(2).right == "a"
    t.nestRight(2).left == 1
    t.nestRight(2).right == Pair.of(2, "a")

    t.pushLeft(2).left == 2
    t.pushLeft(2).right == t
    t.pushRight(2).left == t
    t.pushRight(2).right == 2

    t.mapLeft { it + 1 }.left == 2
    t.mapLeft { it + 1 }.right == "a"
    t.mapRight { it * 2 }.left == 1
    t.mapRight { it * 2 }.right == "aa"

	for _, fn := range typecheck.Target.Funcs {
		symToFunc[fn.LSym] = fn

		// Make nowritebarrierrec functions BFS roots.
		if fn.Pragma&ir.Nowritebarrierrec != 0 {
			funcs[fn] = nowritebarrierrecCall{}
			q.PushRight(fn.Nname)
		}
		// Check go:nowritebarrier functions.
		if fn.Pragma&ir.Nowritebarrier != 0 && fn.WBPos.IsKnown() {
			base.ErrorfAt(fn.WBPos, 0, "write barrier prohibited")
		}
	}

        return new Pair<L, R>(left, right);
    }

    public <T> Pair<T, Pair<L, R>> pushLeft(T t) {
        return of(t, this);
    }

    public <T> Pair<Pair<L, R>, T> pushRight(T t) {
        return of(this, t);
    }

    public <T> Pair<Pair<T, L>, R> nestLeft(T t) {
        return of(of(t, left), right);
    }

    public <T> Pair<L, Pair<T, R>> nestRight(T t) {