From 5b852e7964989e1bb80409921e8c6bd693ab8998 Mon Sep 17 00:00:00 2001
From: Simon Forman <sforman@hushmail.com>
Date: Mon, 10 Oct 2022 22:23:19 -0700
Subject: [PATCH] Minor cleanup.

---
 docs/notebooks/BigInts.ipynb | 88 ++++++++++++++++++++----------------
 1 file changed, 49 insertions(+), 39 deletions(-)

diff --git a/docs/notebooks/BigInts.ipynb b/docs/notebooks/BigInts.ipynb
index c353e3a..90bddb3 100644
--- a/docs/notebooks/BigInts.ipynb
+++ b/docs/notebooks/BigInts.ipynb
@@ -484,7 +484,7 @@
     "- We're tearing down two lists simultaneously.\n",
     "- They might not be the same length.\n",
     "\n",
-    "There are two base cases: two empty lists or one empty list, the recursive branch is taken only if both lists at non-empty.\n",
+    "There are two base cases: two empty lists or one empty list, the recursive branch is taken only if both lists are non-empty.\n",
     "\n",
     "    bool [a ...] [b ...] P\n",
     "\n",
@@ -955,7 +955,7 @@
     "    carry [n ...] add-carry-to-digits\n",
     "    carry [n ...] [_actd_P] [_actd_THEN] [_actd_R0] [_actd_R1] genrec\n",
     "\n",
-    "The predicate is the carry flag itself inverted, but when we recur we need to check if the list is non-empty because it will eventually be empty or the carry flag will be false:\n",
+    "The predicate is the carry flag itself inverted (but when we recur we will need to check if the list is non-empty because it may eventually be empty):\n",
     "\n",
     "    _actd_P ≡ pop not\n",
     "\n",
@@ -992,52 +992,22 @@
   },
   {
    "cell_type": "markdown",
-   "id": "379d88db",
+   "id": "d5898c6a",
    "metadata": {},
    "source": [
     "If it's empty...\n",
     "\n",
     "       true [] R0.else [add-carry-to-digits] R1\n",
     "    ----------------------------------------------\n",
-    "           false [1] [add-carry-to-digits] R1\n",
-    "\n",
-    "    R0.else ≡ 1 swons popd false swap"
-   ]
-  },
-  {
-   "cell_type": "markdown",
-   "id": "9f1e5b30",
-   "metadata": {},
-   "source": [
-    "If it's not empty...\n",
-    "\n",
-    "       true [a ...] R0.then [add-carry-to-digits] R1\n",
-    "    -------------------------------------------------------------\n",
-    "       true 0 a add-with-carry [...1] [add-carry-to-digits] R1\n",
-    "    -------------------------------------------------------------\n",
-    "       (a+1) carry [...1] [add-carry-to-digits] R1"
-   ]
-  },
-  {
-   "cell_type": "markdown",
-   "id": "d5898c6a",
-   "metadata": {},
-   "source": [
-    "Ah ha!?  How to get that `(a+1)` back into the list!?\n",
-    "\n",
-    "If it's empty...\n",
-    "\n",
-    "       true [] R0.else [add-carry-to-digits] R1\n",
-    "    ------------------------------------------------\n",
-    "          1 false [] [add-carry-to-digits] i cons\n",
+    "        1 false [] [add-carry-to-digits] i cons\n",
     "\n",
     "and\n",
     "\n",
-    "       true [a ...] R0.then [add-carry-to-digits] i cons\n",
-    "    -------------------------------------------------------------\n",
-    "       true 0 a add-with-carry [...1] [add-carry-to-digits] i cons\n",
-    "    -------------------------------------------------------------\n",
-    "       (a+1) carry [...1] [add-carry-to-digits] i cons"
+    "                true [a ...] R0.then [add-carry-to-digits] i cons\n",
+    "    ----------------------------------------------------------------\n",
+    "       true 0 a add-with-carry [...] [add-carry-to-digits] i cons\n",
+    "    ----------------------------------------------------------------\n",
+    "                   (a+1) carry [...] [add-carry-to-digits] i cons"
    ]
   },
   {
@@ -1546,6 +1516,46 @@
    "source": [
     "Bitchin'"
    ]
+  },
+  {
+   "cell_type": "markdown",
+   "id": "f2b707c1",
+   "metadata": {},
+   "source": [
+    "## Appendix: Source Code\n",
+    "\n",
+    "    base 2147483648\n",
+    "    ditch-empty-list [bool] [popd] [pop] ifte\n",
+    "    bool_to_int [0] [1] branch\n",
+    "    uncons-two [uncons] ii swapd\n",
+    "\n",
+    "    add-with-carry _a0 _a1\n",
+    "    _a0 [bool_to_int] dipd + +\n",
+    "    _a1 base [mod] [>=] clop\n",
+    "\n",
+    "    add-carry-to-digits [pop not] [popd] [_actd_R0] [i cons] genrec\n",
+    "    _actd_R0 [bool] [_actd_R0.then] [_actd_R0.else] ifte\n",
+    "    _actd_R0.else popd 1 false rolldown\n",
+    "    _actd_R0.then 0 swap uncons [add-with-carry] dip\n",
+    "\n",
+    "    add-digits initial-carry add-digits'\n",
+    "    initial-carry false rollup\n",
+    "    add-digits' [P] [THEN] [R0] [i cons] genrec\n",
+    "    P [bool] ii & not\n",
+    "    THEN [P'] [THEN'] [ELSE] ifte\n",
+    "    R0 uncons-two [add-with-carry] dipd\n",
+    "    P' [bool] ii |\n",
+    "    THEN' ditch-empty-list add-carry-to-digits\n",
+    "    ELSE pop swap [] [1 swons] branch\n"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "id": "84affe68",
+   "metadata": {},
+   "outputs": [],
+   "source": []
   }
  ],
  "metadata": {