convert AST_Seq from binary tree to array (#1460)

- rename `AST_Seq` to `AST_Sequence`
- raise default sequences_limit from 200 to 800

lib/ast.js

@@ -613,68 +613,16 @@ var AST_New = DEFNODE("New", null, {
     $documentation: "An object instantiation.  Derives from a function call since it has exactly the same properties"
 }, AST_Call);
 
-var AST_Seq = DEFNODE("Seq", "car cdr", {
-    $documentation: "A sequence expression (two comma-separated expressions)",
+var AST_Sequence = DEFNODE("Sequence", "expressions", {
+    $documentation: "A sequence expression (comma-separated expressions)",
     $propdoc: {
-        car: "[AST_Node] first element in sequence",
-        cdr: "[AST_Node] second element in sequence"
-    },
-    $cons: function(x, y) {
-        var seq = new AST_Seq(x);
-        seq.car = x;
-        seq.cdr = y;
-        return seq;
-    },
-    $from_array: function(array) {
-        if (array.length == 0) return null;
-        if (array.length == 1) return array[0].clone();
-        var list = null;
-        for (var i = array.length; --i >= 0;) {
-            list = AST_Seq.cons(array[i], list);
-        }
-        var p = list;
-        while (p) {
-            if (p.cdr && !p.cdr.cdr) {
-                p.cdr = p.cdr.car;
-                break;
-            }
-            p = p.cdr;
-        }
-        return list;
-    },
-    to_array: function() {
-        var p = this, a = [];
-        while (p) {
-            a.push(p.car);
-            if (p.cdr && !(p.cdr instanceof AST_Seq)) {
-                a.push(p.cdr);
-                break;
-            }
-            p = p.cdr;
-        }
-        return a;
-    },
-    add: function(node) {
-        var p = this;
-        while (p) {
-            if (!(p.cdr instanceof AST_Seq)) {
-                var cell = AST_Seq.cons(p.cdr, node);
-                return p.cdr = cell;
-            }
-            p = p.cdr;
-        }
-    },
-    len: function() {
-        if (this.cdr instanceof AST_Seq) {
-            return this.cdr.len() + 1;
-        } else {
-            return 2;
-        }
+        expressions: "[AST_Node*] array of expressions (at least two)"
     },
     _walk: function(visitor) {
         return visitor._visit(this, function(){
-            this.car._walk(visitor);
-            if (this.cdr) this.cdr._walk(visitor);
+            this.expressions.forEach(function(node) {
+                node._walk(visitor);
+            });
         });
     }
 });