starting to cache fancy switch values -- fixing issue #171

lib/lexer.js

@@ -355,7 +355,7 @@
   // parameter identifiers in order to avoid this. Also, parameter lists can
   // make use of splats.
   lex.prototype.tag_parameters = function tag_parameters() {
-    var i, tok;
+    var _a, i, tok;
     if (this.tag() !== ')') {
       return null;
     }
@@ -366,11 +366,11 @@
       if (!tok) {
         return null;
       }
-      if (tok[0] === 'IDENTIFIER') {
+      if ((_a = tok[0]) === 'IDENTIFIER') {
         tok[0] = 'PARAM';
-      } else if (tok[0] === ')') {
+      } else if (_a === ')') {
         tok[0] = 'PARAM_END';
-      } else if (tok[0] === '(') {
+      } else if (_a === '(') {
         return (tok[0] = 'PARAM_START');
       }
     }

lib/nodes.js

@@ -1216,23 +1216,34 @@
       this.tags.statement = true;
       return this;
     },
-    // Rewrite a chain of IfNodes with their switch condition for equality.
+    // Tag a chain of IfNodes with their switch condition for equality.
     rewrite_condition: function rewrite_condition(expression) {
-      var _a, _b, _c, cond;
+      this.switcher = expression;
+      return this;
+    },
+    // Rewrite a chain of IfNodes with their switch condition for equality.
+    rewrite_switch: function rewrite_switch(o) {
+      var _a, _b, assigner, cond, i, variable;
+      assigner = this.switcher;
+      if (!(this.switcher.unwrap() instanceof LiteralNode)) {
+        variable = new LiteralNode(o.scope.free_variable());
+        assigner = new AssignNode(variable, this.switcher);
+        this.switcher = variable;
+      }
       this.condition = (function() {
         if (this.multiple) {
           _a = []; _b = this.condition;
-          for (_c = 0; _c < _b.length; _c++) {
-            cond = _b[_c];
-            _a.push(new OpNode('is', expression, cond));
+          for (i = 0; i < _b.length; i++) {
+            cond = _b[i];
+            _a.push(new OpNode('is', (i === 0 ? assigner : this.switcher), cond));
           }
           return _a;
         } else {
-          return new OpNode('is', expression, this.condition);
+          return new OpNode('is', assigner, this.condition);
         }
       }).call(this);
       if (this.is_chain()) {
-        this.else_body.rewrite_condition(expression);
+        this.else_body.rewrite_condition(this.switcher);
       }
       return this;
     },
@@ -1269,6 +1280,9 @@
     // force sub-else bodies into statement form.
     compile_statement: function compile_statement(o) {
       var body, child, com_dent, cond_o, else_part, if_dent, if_part, prefix;
+      if (this.switcher) {
+        this.rewrite_switch(o);
+      }
       child = del(o, 'chain_child');
       cond_o = merge(o);
       del(cond_o, 'returns');

lib/rewriter.js

@@ -156,22 +156,23 @@
     brackets = [0];
     return this.scan_tokens((function(__this) {
       var __func = function(prev, token, post, i) {
-        if (token[0] === 'CALL_START') {
+        var _i;
+        if ((_i = token[0]) === 'CALL_START') {
           parens.push(0);
-        } else if (token[0] === 'INDEX_START') {
+        } else if (_i === 'INDEX_START') {
           brackets.push(0);
-        } else if (token[0] === '(') {
+        } else if (_i === '(') {
           parens[parens.length - 1] += 1;
-        } else if (token[0] === '[') {
+        } else if (_i === '[') {
           brackets[brackets.length - 1] += 1;
-        } else if (token[0] === ')') {
+        } else if (_i === ')') {
           if (parens[parens.length - 1] === 0) {
             parens.pop();
             token[0] = 'CALL_END';
           } else {
             parens[parens.length - 1] -= 1;
           }
-        } else if (token[0] === ']') {
+        } else if (_i === ']') {
           if (brackets[brackets.length - 1] === 0) {
             brackets.pop();
             token[0] = 'INDEX_END';

src/nodes.coffee

@@ -970,13 +970,24 @@ IfNode: exports.IfNode: inherit Node, {
     @tags.statement: true
     this
 
-  # Rewrite a chain of IfNodes with their switch condition for equality.
+  # Tag a chain of IfNodes with their switch condition for equality.
   rewrite_condition: (expression) ->
+    @switcher: expression
+    this
+
+  # Rewrite a chain of IfNodes with their switch condition for equality.
+  rewrite_switch: (o) ->
+    assigner: @switcher
+    if not (@switcher.unwrap() instanceof LiteralNode)
+      variable: new LiteralNode(o.scope.free_variable())
+      assigner: new AssignNode(variable, @switcher)
+      @switcher: variable
     @condition: if @multiple
-      new OpNode('is', expression, cond) for cond in @condition
+      for cond, i in @condition
+        new OpNode('is', (if i is 0 then assigner else @switcher), cond)
     else
-      new OpNode('is', expression, @condition)
-    @else_body.rewrite_condition(expression) if @is_chain()
+      new OpNode('is', assigner, @condition)
+    @else_body.rewrite_condition(@switcher) if @is_chain()
     this
 
   # Rewrite a chain of IfNodes to add a default case as the final else.
@@ -1003,6 +1014,7 @@ IfNode: exports.IfNode: inherit Node, {
   # Compile the IfNode as a regular if-else statement. Flattened chains
   # force sub-else bodies into statement form.
   compile_statement: (o) ->
+    @rewrite_switch(o) if @switcher
     child:        del o, 'chain_child'
     cond_o:       merge o
     del cond_o, 'returns'

test/test_switch.coffee

@@ -29,3 +29,15 @@ ok func(2)
 ok func(6)
 ok !func(3)
 ok !func(8)
+
+
+# Should cache the switch value, if anything fancier than a literal.
+num: 5
+result: switch num += 5
+  when 5 then false
+  when 15 then false
+  when 10 then true
+  else false
+
+ok result
+