closes #86; implemented named destructuring

Author: satyr

extras/coco.js

@@ -956,6 +956,13 @@ List = (function(_super){
   List.displayName = 'List';
   var prototype = __extends(List, _super).prototype;
   prototype.children = ['items'];
+  prototype.show = function(){
+    return this.name;
+  };
+  prototype.named = function(name){
+    this.name = name;
+    return this;
+  };
   prototype.isEmpty = function(){
     return !this.items.length;
   };
@@ -1686,12 +1693,15 @@ exports.Assign = Assign = (function(_super){
     return If(test, left).addElse(put).compileNode(o);
   };
   prototype.compileDestructuring = function(o, left){
-    var items, len, ret, rite, rref, cache, list, code;
+    var items, len, ret, rite, that, cache, rref, list, code;
     items = left.items;
     len = items.length;
     ret = o.level && !this['void'];
     rite = this.right.compile(o, len === 1 ? LEVEL_CALL : LEVEL_LIST);
-    if ((ret || len > 1) && (!ID.test(rite) || left.assigns(rite))) {
+    if (that = left.name) {
+      cache = that + " = " + rite;
+      o.scope.declare(rite = that);
+    } else if ((ret || len > 1) && (!ID.test(rite) || left.assigns(rite))) {
       cache = (rref = o.scope.temporary('ref')) + " = " + rite;
       rite = rref;
     }
@@ -2112,7 +2122,7 @@ exports.Fun = Fun = (function(_super){
         if (vr.isEmpty()) {
           vr = Var(scope.temporary('arg'));
         } else if (!(vr instanceof Var)) {
-          v = Var(vr.varName() || scope.temporary('arg'));
+          v = Var((_ref = vr.name, delete vr.name, _ref) || vr.varName() || scope.temporary('arg'));
           assigns.push(Assign(vr, df ? Op(p.op, v, p.second) : v));
           vr = v;
         } else if (df) {

lib/ast.js

@@ -38,6 +38,10 @@ bnf = {
       return L(Arr($2));
     }), o('{ Properties OptComma }', function(){
       return L(Obj($2));
+    }), o('[ ArgList    OptComma ] LABEL', function(){
+      return L(Arr($2)).named($5);
+    }), o('{ Properties OptComma } LABEL', function(){
+      return L(Obj($2)).named($5);
     })
   ],
   Key: [o('KeyBase'), o('Parenthetical')],

lib/grammar.js

@@ -572,9 +572,13 @@ class exports.Call extends Node
 #### List
 # An abstract node for a list of comma-separated items.
 class List extends Node
-  children : [\items]
-  isEmpty  : -> not @items.length
-  assigns  : -> return true if node.assigns it for node of @items
+  children: [\items]
+
+  show  : -> @name
+  named : (@name) -> this
+
+  isEmpty : -> not @items.length
+  assigns : -> return true if node.assigns it for node of @items
 
   @compile = (o, items) ->
     switch items.length
@@ -1011,7 +1015,10 @@ class exports.Assign extends Node
   compileDestructuring: (o, left) ->
     {items} = left; len = items.length; ret = o.level and not @void
     rite = @right.compile o, if len is 1 then LEVEL_CALL else LEVEL_LIST
-    if (ret or len > 1) and (not ID.test rite or left.assigns rite)
+    if left.name
+      cache = "#that = #rite"
+      o.scope.declare rite = that
+    else if (ret or len > 1) and (not ID.test rite or left.assigns rite)
       cache = "#{ rref = o.scope.temporary \ref } = #rite"
       rite  = rref
     list = @"rend#{ left..displayName }" o, items, rite
@@ -1279,7 +1286,7 @@ class exports.Fun extends Node
         if vr.isEmpty()
           vr = Var scope.temporary \arg
         else if vr not instanceof Var
-          v = Var vr.varName() || scope.temporary \arg
+          v = Var delete vr.name || vr.varName() || scope.temporary \arg
           assigns.push Assign vr, if df then Op p.op, v, p.second else v
           vr = v
         else if df

lib/parser.js

@@ -76,6 +76,9 @@ bnf =
   List:
     o '[ ArgList    OptComma ]' -> L Arr $2
     o '{ Properties OptComma }' -> L Obj $2
+    # Can be labeled to perform named destructuring.
+    o '[ ArgList    OptComma ] LABEL' -> L Arr $2 .named $5
+    o '{ Properties OptComma } LABEL' -> L Obj $2 .named $5
 
   # **Key** represents a property name, before `:` or after `.`.
   Key:

src/ast.co

@@ -293,3 +293,13 @@ o = d: 0, e: 1
 o{d, e} &&*= d: 2, e: 3
 eq 0 o.d
 eq 3 o.e
+
+
+### Named Destructuring
+[b, c]:a = [0 1]
+eq b, a.0
+eq c, a.1
+
+let {p, q}:o = {2 3}
+  eq p, o.p
+  eq q, o.q