Possible fix for counter-example found on stackless algo

The following term:

/ #f #x /f /f x #A #B #C //B A C

Caused the stackless algorithm to behave incorrectly. It halted
before reducing all active ports. This patch fixes the algorithm
for that specific term, but I'm not sure anymore it works for the
same terms that the stack version does. A test suite is necessary.

Author: VictorTaelin

package.json

@@ -1,6 +1,6 @@
 {
   "name": "abstract-algorithm",
-  "version": "0.1.20",
+  "version": "0.1.21",
   "description": "Abstract-algorithm for optional reduction of stratifiable lambda terms",
   "main": "src/lambda-calculus.js",
   "bin": {

src/abstract-combinators.js

@@ -50,23 +50,30 @@ function link(net, a, b) {
 
 function reduce(net) {
   var next = net.nodes[0];
-  var prev, back;
+  var prev, back, nextMeta, nextSlot;
+  var i = 0;
   while (next > 0) {
     prev = enterPort(net, next);
     next = enterPort(net, prev);
-    if (slot(next) === 0) {
-      if (slot(prev) === 0 && node(prev) !== 0) {
-        back = enterPort(net, port(node(prev), meta(net, node(prev))));
-        rewrite(net, node(prev), node(next), net.stats);
-        next = enterPort(net, back);
-      } else {
-        setMeta(net, node(next), 1);
-        next = enterPort(net, port(node(next), 1));
-      }
+    ++i;
+    if (slot(next) === 0 && slot(prev) === 0 && node(prev) !== 0) {
+      back = enterPort(net, port(node(prev), meta(net, node(prev))));
+      rewrite(net, node(prev), node(next), net.stats);
+      next = enterPort(net, back);
     } else {
-      var metaNext = meta(net, node(next));
-      setMeta(net, node(next), metaNext === 0 ? slot(next) : metaNext + 1);
-      next = enterPort(net, port(node(next), metaNext === 1 ? 2 : 0));
+      switch (slot(next) * 3 + meta(net, node(next))) {
+        case 0 * 3 + 0: nextSlot = 1; nextMeta = 1; break;
+        case 0 * 3 + 1: nextSlot = 2; nextMeta = 2; break;
+        case 0 * 3 + 2: nextSlot = 1; nextMeta = 1; break;
+        case 1 * 3 + 0: nextSlot = 0; nextMeta = 1; break;
+        case 1 * 3 + 1: nextSlot = 2; nextMeta = 2; break;
+        case 1 * 3 + 2: nextSlot = 0; nextMeta = 3; break;
+        case 2 * 3 + 0: nextSlot = 0; nextMeta = 2; break;
+        case 2 * 3 + 1: nextSlot = 2; nextMeta = 2; break;
+        case 2 * 3 + 2: nextSlot = 0; nextMeta = 3; break;
+      }
+      setMeta(net, node(next), nextMeta);
+      next = enterPort(net, port(node(next), nextSlot));
     }
     ++net.stats.loops;
   }
@@ -110,18 +117,6 @@ function rewrite(net, A, B) {
   net.stats.rules += 1;
 }
 
-function show(net) {
-  console.log(net.stats);
-  for (var i=0; i < net.nodes.length;i+=4) {
-    if (net.reuse.some(x => x === i>>2)) {
-      console.log(i>>2);
-      continue;
-    }
-    [a,b,c,d] = net.nodes.slice(i, i+4)
-    console.log(i>>2, `${a>>2}:${a&3} ${b>>2}:${b&3} ${c>>2}:${c&3} ${d>>2}:${d&3}`);
-  }
-}
-
 module.exports = {
   port,
   node,

src/lambda-calculus.js

@@ -79,7 +79,7 @@ const toString = (term, bruijn) => {
 
 const toNet = term => {
   var kind = 1;
-  var net = I.newNet([0, 1, 2, 0]);
+  var net = I.newNet([0, 2, 1, 4]);
   var ptr = (function encode(term, scope){
     switch (term.tag){
       // Arg