Exposed car, cdr, cadr, etc. in lisp

elisp/list.js

@@ -83,43 +83,22 @@ LispCons.prototype.unlist = function() {
 
 LispCons.prototype.nth = function(n) {
     var i = 0,
-	e,
-	cons = this;
-//    print('[LispCons.nth] calling cons.isNil - cons: ' + cons + ' - _cdr: ' + cons._cdr);
+	cons = this,
+        e = cons.car();
     while (i <= n && !cons.isNil()) {
 	e = cons.car();
 	cons = cons.cdr();
 	++i;
     }
-    return n > (i-1) ? type.NIL : e;
+    return e;
 };
 
 LispCons.prototype.nthcdr = function(n) {
-    var e = this.cdr(),
-	i = 0;
-//    print('[LispCons.nthcdr] calling e.isNil - e: ' + e + ' - _cdr: ' + e._cdr);
-    while (i < n && !e.isNil()) {
+    var e = this,
+	i = 1;
+    while (i <= n && !e.isNil()) {
 	e = e.cdr();
 	++i;
     }
-    return n > i ? type.NIL : e;
+    return e;
 };
-
-
-// Make NIL act like a list ... there's got to be a better way
-
-NIL.unlist = function(){return [];};
-
-NIL._length = 0;
-NIL.length = function(){return 0;};
-
-NIL.reduce = function(accum){return accum;};
-
-nilMethods = ['car', 'cdr', 'cadr', 'caddr', 'cadddr',
-              'last', 'map', 'nthcdr', 'nth'];
-
-var nilFn = function(){return NIL;};
-
-for (var method in nilMethods) {
-    NIL[method] = nilFn;
-}

elisp/primitives.js

@@ -46,18 +46,62 @@ var notFunc = function(fn) {
 };
 exports.notFunc = notFunc;
 
-var makePrimitiveBooleanFunc = function(fn) {
+var makeBooleanFunc = function(fn) {
     return function(x){ return x[fn]() ? type.T : type.NIL; };
 };
-exports.makePrimitiveBooleanFunc = makePrimitiveBooleanFunc;
+exports.makeBooleanFunc = makeBooleanFunc;
+
+// TODO FIXME make NIL act like the empty list
+var makeNilFn = function(fn) {
+    return function(arg){ return arg.isNil() ? arg : arg[fn](); };
+};
+
+var makeZeroFn = function(fn) {
+    return function(arg){ return arg.isNil() ? new type.LispNumber(0) : arg[fn](); };
+};
 
 init.hook('Define Primitive Variables and Functions', function() {
-    var type = require('elisp/types');
-    definePrimitive('consp', ['symbol'], makePrimitiveBooleanFunc('isCons'),
-        "Return T if symbol is a cons, nil otherwise.");
 
-    definePrimitive('atom', ['symbol'], makePrimitiveBooleanFunc('isAtom'),
-        "Return T if symbol is not a cons or is nil, nil otherwise.");
+    definePrimitive('consp', ['symbol'], makeBooleanFunc('isCons'),
+        "Return t if symbol is a cons, nil otherwise.");
+    
+    definePrimitive('atom', ['symbol'], makeBooleanFunc('isAtom'),
+        "Return t if symbol is not a cons or is nil, nil otherwise.");
+
+
+// list functions
+    
+    definePrimitive('car', ['arg'], makeNilFn('car'),
+        "Return the car of list.  If arg is nil, return nil. \
+Error if arg is not nil and not a cons cell.");
+
+    definePrimitive('cdr', ['arg'], makeNilFn('cdr'),
+	"Return the cdr of list.  If arg is nil, return nil. \
+Error if arg is not nil and not a cons cell.");
+
+    definePrimitive('nth', ['n', 'arg'], function(n, arg){
+	return arg.isNil() ? arg : arg.nth(n.value());
+    }, "Return the nth element of list. \
+n counts from zero.  If list is not that long, nil is returned.");
+
+    definePrimitive('nthcdr', ['n', 'arg'], function(n, arg){
+	return arg.isNil() ? arg : arg.nthcdr(n.value());
+    }, "Take cdr n times on list, returns the result.");
+
+    definePrimitive('cadr', ['arg'], makeNilFn('cadr'),
+	"Return the car of the cdr of x.");
+
+    definePrimitive('caddr', ['arg'], makeNilFn('caddr'),
+	"Return the car of the cdr of the cdr of x.");
+
+    definePrimitive('cadddr', ['arg'], makeNilFn('cadddr'),
+	"Return the car of the cdr of the cdr of the cdr of x.");
+
+//////////
+///// FIXME new symbol table! this makes the current one barf, because it sucks
+/////
+//     definePrimitive('length', ['arg'], makeZeroFn('length'),
+// 	"Return the length of list.");
 
     definePrimitive('symbol-name', ['symbol'],
         function(symbol) { return new type.LispString(symbol.symbolName()); },