10 files changed, 329 insertions, 85 deletions

diff --git a/lib/handlebars/compiler/ast.js b/lib/handlebars/compiler/ast.js
index b6c3a03..ce5ee11 100644
--- a/lib/handlebars/compiler/ast.js
+++ b/lib/handlebars/compiler/ast.js
@@ -46,7 +46,6 @@ var AST = {
   MustacheNode: function(rawParams, hash, open, strip, locInfo) {
     LocationInfo.call(this, locInfo);
     this.type = "mustache";
-    this.hash = hash;
     this.strip = strip;
 
     // Open may be a string parsed from the parser or a passed boolean flag
@@ -58,6 +57,25 @@ var AST = {
       this.escaped = !!open;
     }
 
+    if (rawParams instanceof AST.SexprNode) {
+      this.sexpr = rawParams;
+    } else {
+      // Support old AST API
+      this.sexpr = new AST.SexprNode(rawParams, hash);
+    }
+
+    // Support old AST API that stored this info in MustacheNode
+    this.id = this.sexpr.id;
+    this.params = this.sexpr.params;
+    this.hash = this.sexpr.hash;
+    this.eligibleHelper = this.sexpr.eligibleHelper;
+    this.isHelper = this.sexpr.isHelper;
+  },
+
+  SexprNode: function(rawParams, hash) {
+    this.type = "sexpr";
+    this.hash = hash;
+
     var id = this.id = rawParams[0];
     var params = this.params = rawParams.slice(1);
 
@@ -84,8 +102,8 @@ var AST = {
   },
 
   BlockNode: function(mustache, program, inverse, close, locInfo) {
-    if(mustache.id.original !== close.path.original) {
-      throw new Exception(mustache.id.original + " doesn't match " + close.path.original);
+    if(mustache.sexpr.id.original !== close.path.original) {
+      throw new Exception(mustache.sexpr.id.original + " doesn't match " + close.path.original);
     }
 
     LocationInfo.call(this, locInfo);
diff --git a/lib/handlebars/compiler/compiler.js b/lib/handlebars/compiler/compiler.js
index 259c543..00353a8 100644
--- a/lib/handlebars/compiler/compiler.js
+++ b/lib/handlebars/compiler/compiler.js
@@ -156,12 +156,13 @@ Compiler.prototype = {
       inverse = this.compileProgram(inverse);
     }
 
-    var type = this.classifyMustache(mustache);
+    var sexpr = mustache.sexpr;
+    var type = this.classifySexpr(sexpr);
 
     if (type === "helper") {
-      this.helperMustache(mustache, program, inverse);
+      this.helperSexpr(sexpr, program, inverse);
     } else if (type === "simple") {
-      this.simpleMustache(mustache);
+      this.simpleSexpr(sexpr);
 
       // now that the simple mustache is resolved, we need to
       // evaluate it by executing `blockHelperMissing`
@@ -170,7 +171,7 @@ Compiler.prototype = {
       this.opcode('emptyHash');
       this.opcode('blockValue');
     } else {
-      this.ambiguousMustache(mustache, program, inverse);
+      this.ambiguousSexpr(sexpr, program, inverse);
 
       // now that the simple mustache is resolved, we need to
       // evaluate it by executing `blockHelperMissing`
@@ -198,6 +199,12 @@ Compiler.prototype = {
         }
         this.opcode('getContext', val.depth || 0);
         this.opcode('pushStringParam', val.stringModeValue, val.type);
+
+        if (val.type === 'sexpr') {
+          // Subexpressions get evaluated and passed in
+          // in string params mode.
+          this.sexpr(val);
+        }
       } else {
         this.accept(val);
       }
@@ -226,26 +233,17 @@ Compiler.prototype = {
   },
 
   mustache: function(mustache) {
-    var options = this.options;
-    var type = this.classifyMustache(mustache);
-
-    if (type === "simple") {
-      this.simpleMustache(mustache);
-    } else if (type === "helper") {
-      this.helperMustache(mustache);
-    } else {
-      this.ambiguousMustache(mustache);
-    }
+    this.sexpr(mustache.sexpr);
 
-    if(mustache.escaped && !options.noEscape) {
+    if(mustache.escaped && !this.options.noEscape) {
       this.opcode('appendEscaped');
     } else {
       this.opcode('append');
     }
   },
 
-  ambiguousMustache: function(mustache, program, inverse) {
-    var id = mustache.id,
+  ambiguousSexpr: function(sexpr, program, inverse) {
+    var id = sexpr.id,
         name = id.parts[0],
         isBlock = program != null || inverse != null;
 
@@ -257,8 +255,8 @@ Compiler.prototype = {
     this.opcode('invokeAmbiguous', name, isBlock);
   },
 
-  simpleMustache: function(mustache) {
-    var id = mustache.id;
+  simpleSexpr: function(sexpr) {
+    var id = sexpr.id;
 
     if (id.type === 'DATA') {
       this.DATA(id);
@@ -274,9 +272,9 @@ Compiler.prototype = {
     this.opcode('resolvePossibleLambda');
   },
 
-  helperMustache: function(mustache, program, inverse) {
-    var params = this.setupFullMustacheParams(mustache, program, inverse),
-        name = mustache.id.parts[0];
+  helperSexpr: function(sexpr, program, inverse) {
+    var params = this.setupFullMustacheParams(sexpr, program, inverse),
+        name = sexpr.id.parts[0];
 
     if (this.options.knownHelpers[name]) {
       this.opcode('invokeKnownHelper', params.length, name);
@@ -287,6 +285,18 @@ Compiler.prototype = {
     }
   },
 
+  sexpr: function(sexpr) {
+    var type = this.classifySexpr(sexpr);
+
+    if (type === "simple") {
+      this.simpleSexpr(sexpr);
+    } else if (type === "helper") {
+      this.helperSexpr(sexpr);
+    } else {
+      this.ambiguousSexpr(sexpr);
+    }
+  },
+
   ID: function(id) {
     this.addDepth(id.depth);
     this.opcode('getContext', id.depth);
@@ -349,14 +359,14 @@ Compiler.prototype = {
     }
   },
 
-  classifyMustache: function(mustache) {
-    var isHelper   = mustache.isHelper;
-    var isEligible = mustache.eligibleHelper;
+  classifySexpr: function(sexpr) {
+    var isHelper   = sexpr.isHelper;
+    var isEligible = sexpr.eligibleHelper;
     var options    = this.options;
 
     // if ambiguous, we can possibly resolve the ambiguity now
     if (isEligible && !isHelper) {
-      var name = mustache.id.parts[0];
+      var name = sexpr.id.parts[0];
 
       if (options.knownHelpers[name]) {
         isHelper = true;
@@ -383,35 +393,27 @@ Compiler.prototype = {
 
         this.opcode('getContext', param.depth || 0);
         this.opcode('pushStringParam', param.stringModeValue, param.type);
+
+        if (param.type === 'sexpr') {
+          // Subexpressions get evaluated and passed in
+          // in string params mode.
+          this.sexpr(param);
+        }
       } else {
         this[param.type](param);
       }
     }
   },
 
-  setupMustacheParams: function(mustache) {
-    var params = mustache.params;
-    this.pushParams(params);
-
-    if(mustache.hash) {
-      this.hash(mustache.hash);
-    } else {
-      this.opcode('emptyHash');
-    }
-
-    return params;
-  },
-
-  // this will replace setupMustacheParams when we're done
-  setupFullMustacheParams: function(mustache, program, inverse) {
-    var params = mustache.params;
+  setupFullMustacheParams: function(sexpr, program, inverse) {
+    var params = sexpr.params;
     this.pushParams(params);
 
     this.opcode('pushProgram', program);
     this.opcode('pushProgram', inverse);
 
-    if(mustache.hash) {
-      this.hash(mustache.hash);
+    if (sexpr.hash) {
+      this.hash(sexpr.hash);
     } else {
       this.opcode('emptyHash');
     }
diff --git a/lib/handlebars/compiler/javascript-compiler.js b/lib/handlebars/compiler/javascript-compiler.js
index 159a38b..d920d52 100644
--- a/lib/handlebars/compiler/javascript-compiler.js
+++ b/lib/handlebars/compiler/javascript-compiler.js
@@ -244,9 +244,6 @@ JavaScriptCompiler.prototype = {
     var current = this.topStack();
     params.splice(1, 0, current);
 
-    // Use the options value generated from the invocation
-    params[params.length-1] = 'options';
-
     this.pushSource("if (!" + this.lastHelper + ") { " + current + " = blockHelperMissing.call(" + params.join(", ") + "); }");
   },
 
@@ -398,10 +395,14 @@ JavaScriptCompiler.prototype = {
 
     this.pushString(type);
 
-    if (typeof string === 'string') {
-      this.pushString(string);
-    } else {
-      this.pushStackLiteral(string);
+    // If it's a subexpression, the string result
+    // will be pushed after this opcode.
+    if (type !== 'sexpr') {
+      if (typeof string === 'string') {
+        this.pushString(string);
+      } else {
+        this.pushStackLiteral(string);
+      }
     }
   },
 
@@ -409,8 +410,8 @@ JavaScriptCompiler.prototype = {
     this.pushStackLiteral('{}');
 
     if (this.options.stringParams) {
-      this.register('hashTypes', '{}');
-      this.register('hashContexts', '{}');
+      this.push('{}'); // hashContexts
+      this.push('{}'); // hashTypes
     }
   },
   pushHash: function() {
@@ -421,9 +422,10 @@ JavaScriptCompiler.prototype = {
     this.hash = undefined;
 
     if (this.options.stringParams) {
-      this.register('hashContexts', '{' + hash.contexts.join(',') + '}');
-      this.register('hashTypes', '{' + hash.types.join(',') + '}');
+      this.push('{' + hash.contexts.join(',') + '}');
+      this.push('{' + hash.types.join(',') + '}');
     }
+
     this.push('{\n    ' + hash.values.join(',\n    ') + '\n  }');
   },
 
@@ -526,7 +528,7 @@ JavaScriptCompiler.prototype = {
   invokeAmbiguous: function(name, helperCall) {
     this.context.aliases.functionType = '"function"';
 
-    this.pushStackLiteral('{}');    // Hash value
+    this.emptyHash();
     var helper = this.setupHelper(0, name, helperCall);
 
     var helperName = this.lastHelper = this.nameLookup('helpers', name, 'helper');
@@ -805,6 +807,11 @@ JavaScriptCompiler.prototype = {
 
     options.push("hash:" + this.popStack());
 
+    if (this.options.stringParams) {
+      options.push("hashTypes:" + this.popStack());
+      options.push("hashContexts:" + this.popStack());
+    }
+
     inverse = this.popStack();
     program = this.popStack();
 
@@ -838,22 +845,13 @@ JavaScriptCompiler.prototype = {
     if (this.options.stringParams) {
       options.push("contexts:[" + contexts.join(",") + "]");
       options.push("types:[" + types.join(",") + "]");
-      options.push("hashContexts:hashContexts");
-      options.push("hashTypes:hashTypes");
     }
 
     if(this.options.data) {
       options.push("data:data");
     }
 
-    options = "{" + options.join(",") + "}";
-    if (useRegister) {
-      this.register('options', options);
-      params.push('options');
-    } else {
-      params.push(options);
-    }
-    return params.join(", ");
+    params.push("{" + options.join(",") + "}");
   }
 };
 
diff --git a/lib/handlebars/compiler/printer.js b/lib/handlebars/compiler/printer.js
index f91ff02..ad55c7d 100644
--- a/lib/handlebars/compiler/printer.js
+++ b/lib/handlebars/compiler/printer.js
@@ -62,8 +62,8 @@ PrintVisitor.prototype.block = function(block) {
   return out;
 };
 
-PrintVisitor.prototype.mustache = function(mustache) {
-  var params = mustache.params, paramStrings = [], hash;
+PrintVisitor.prototype.sexpr = function(sexpr) {
+  var params = sexpr.params, paramStrings = [], hash;
 
   for(var i=0, l=params.length; i<l; i++) {
     paramStrings.push(this.accept(params[i]));
@@ -71,9 +71,13 @@ PrintVisitor.prototype.mustache = function(mustache) {
 
   params = "[" + paramStrings.join(", ") + "]";
 
-  hash = mustache.hash ? " " + this.accept(mustache.hash) : "";
+  hash = sexpr.hash ? " " + this.accept(sexpr.hash) : "";
+
+  return this.accept(sexpr.id) + " " + params + hash;
+};
 
-  return this.pad("{{ " + this.accept(mustache.id) + " " + params + hash + " }}");
+PrintVisitor.prototype.mustache = function(mustache) {
+  return this.pad("{{ " + this.accept(mustache.sexpr) + " }}");
 };
 
 PrintVisitor.prototype.partial = function(partial) {
diff --git a/spec/ast.js b/spec/ast.js
index 0feb3f5..0cb1103 100644
--- a/spec/ast.js
+++ b/spec/ast.js
@@ -68,14 +68,24 @@ describe('ast', function() {
     });
   });
   describe('BlockNode', function() {
+    it('should throw on mustache mismatch (old sexpr-less version)', function() {
+      shouldThrow(function() {
+        var mustacheNode = new handlebarsEnv.AST.MustacheNode([{ original: 'foo'}], null, '{{', {});
+        new handlebarsEnv.AST.BlockNode(mustacheNode, {}, {}, {path: {original: 'bar'}});
+      }, Handlebars.Exception, "foo doesn't match bar");
+    });
     it('should throw on mustache mismatch', function() {
       shouldThrow(function() {
-        new handlebarsEnv.AST.BlockNode({id: {original: 'foo'}}, {}, {}, {path: {original: 'bar'}});
+        var sexprNode = new handlebarsEnv.AST.SexprNode([{ original: 'foo'}], null);
+        var mustacheNode = new handlebarsEnv.AST.MustacheNode(sexprNode, null, '{{', {});
+        new handlebarsEnv.AST.BlockNode(mustacheNode, {}, {}, {path: {original: 'bar'}});
       }, Handlebars.Exception, "foo doesn't match bar");
     });
 
     it('stores location info', function(){
-      var block = new handlebarsEnv.AST.BlockNode({strip: {}, id: {original: 'foo'}},
+      var sexprNode = new handlebarsEnv.AST.SexprNode([{ original: 'foo'}], null);
+      var mustacheNode = new handlebarsEnv.AST.MustacheNode(sexprNode, null, '{{', {});
+      var block = new handlebarsEnv.AST.BlockNode(mustacheNode,
                                                   {strip: {}}, {strip: {}},
                                                   {
                                                     strip: {},
diff --git a/spec/string-params.js b/spec/string-params.js
index 1ebb583..920b855 100644
--- a/spec/string-params.js
+++ b/spec/string-params.js
@@ -142,4 +142,20 @@ describe('string params mode', function() {
 
     equals(result, "STOP ME FROM READING HACKER NEWS I need-a dad.joke wot", "Proper context variable output");
   });
+
+  it("with nested block ambiguous", function() {
+    var template = CompilerContext.compile('{{#with content}}{{#view}}{{firstName}} {{lastName}}{{/view}}{{/with}}', {stringParams: true});
+
+    var helpers  = {
+      with: function(options) {
+        return "WITH";
+      },
+      view: function() {
+        return "VIEW";
+      }
+    };
+
+    var result = template({}, {helpers: helpers});
+    equals(result, "WITH");
+  });
 });
diff --git a/spec/subexpressions.js b/spec/subexpressions.js
new file mode 100644
index 0000000..9c06f94
--- /dev/null
+++ b/spec/subexpressions.js
@@ -0,0 +1,166 @@
+/*global CompilerContext, shouldCompileTo */
+describe('subexpressions', function() {
+  it("arg-less helper", function() {
+    var string   = "{{foo (bar)}}!";
+    var context  = {};
+    var helpers  = {
+      foo: function(val) {
+        return val+val;
+      },
+      bar: function() {
+        return "LOL";
+      }
+    };
+    shouldCompileTo(string, [context, helpers], "LOLLOL!");
+  });
+
+  it("helper w args", function() {
+    var string   = '{{blog (equal a b)}}';
+
+    var context  = { bar: "LOL" };
+    var helpers  = {
+      blog: function(val) {
+        return "val is " + val;
+      },
+      equal: function(x, y) {
+        return x === y;
+      }
+    };
+    shouldCompileTo(string, [context, helpers], "val is true");
+  });
+
+  it("supports much nesting", function() {
+    var string   = '{{blog (equal (equal true true) true)}}';
+
+    var context  = { bar: "LOL" };
+    var helpers  = {
+      blog: function(val) {
+        return "val is " + val;
+      },
+      equal: function(x, y) {
+        return x === y;
+      }
+    };
+    shouldCompileTo(string, [context, helpers], "val is true");
+  });
+
+  it("provides each nested helper invocation its own options hash", function() {
+    var string = '{{equal (equal true true) true}}';
+
+    var lastOptions = null;
+    var helpers  = {
+      equal: function(x, y, options) {
+        if (!options || options === lastOptions) {
+          throw new Error("options hash was reused");
+        }
+        lastOptions = options;
+        return x === y;
+      }
+    };
+    shouldCompileTo(string, [{}, helpers], "true");
+  });
+
+  it("with hashes", function() {
+    var string   = '{{blog (equal (equal true true) true fun="yes")}}';
+
+    var context  = { bar: "LOL" };
+    var helpers  = {
+      blog: function(val) {
+        return "val is " + val;
+      },
+      equal: function(x, y) {
+        return x === y;
+      }
+    };
+    shouldCompileTo(string, [context, helpers], "val is true");
+  });
+
+  it("as hashes", function() {
+    var string   = '{{blog fun=(equal true true)}}';
+
+    var helpers  = {
+      blog: function(options) {
+        return "val is " + options.hash.fun;
+      },
+      equal: function(x, y) {
+        return x === y;
+      }
+    };
+    shouldCompileTo(string, [{}, helpers], "val is true");
+  });
+
+  it("in string params mode,", function() {
+    var template = CompilerContext.compile('{{snog (blorg foo x=y) yeah a=b}}', {stringParams: true});
+
+    var helpers = {
+      snog: function(a, b, options) {
+        equals(a, 'foo');
+        equals(options.types.length, 2, "string params for outer helper processed correctly");
+        equals(options.types[0], 'sexpr', "string params for outer helper processed correctly");
+        equals(options.types[1], 'ID', "string params for outer helper processed correctly");
+        return a + b;
+      },
+
+      blorg: function(a, options) {
+        equals(options.types.length, 1, "string params for inner helper processed correctly");
+        equals(options.types[0], 'ID', "string params for inner helper processed correctly");
+        return a;
+      }
+    };
+
+    var result = template({
+      foo: {},
+      yeah: {}
+    }, {helpers: helpers});
+
+    equals(result, "fooyeah");
+  });
+
+  it("as hashes in string params mode", function() {
+
+    var template = CompilerContext.compile('{{blog fun=(bork)}}', {stringParams: true});
+
+    var helpers  = {
+      blog: function(options) {
+        equals(options.hashTypes.fun, 'sexpr');
+        return "val is " + options.hash.fun;
+      },
+      bork: function() {
+        return "BORK";
+      }
+    };
+
+    var result = template({}, {helpers: helpers});
+    equals(result, "val is BORK");
+  });
+
+  it("subexpression functions on the context", function() {
+    var string   = "{{foo (bar)}}!";
+    var context  = {
+      bar: function() {
+        return "LOL";
+      }
+    };
+    var helpers  = {
+      foo: function(val) {
+        return val+val;
+      }
+    };
+    shouldCompileTo(string, [context, helpers], "LOLLOL!");
+  });
+
+  it("subexpressions can't just be property lookups", function() {
+    var string   = "{{foo (bar)}}!";
+    var context  = {
+      bar: "LOL"
+    };
+    var helpers  = {
+      foo: function(val) {
+        return val+val;
+      }
+    };
+    shouldThrow(function() {
+      shouldCompileTo(string, [context, helpers], "LOLLOL!");
+    });
+  });
+});
diff --git a/spec/tokenizer.js b/spec/tokenizer.js
index 80f28ab..841a5ab 100644
--- a/spec/tokenizer.js
+++ b/spec/tokenizer.js
@@ -364,4 +364,31 @@ describe('Tokenizer', function() {
   it('does not time out in a mustache when invalid ID characters are used', function() {
     shouldMatchTokens(tokenize("{{foo & }}"), ['OPEN', 'ID']);
   });
+
+  it('tokenizes subexpressions', function() {
+    var result = tokenize("{{foo (bar)}}");
+    shouldMatchTokens(result, ['OPEN', 'ID', 'OPEN_SEXPR', 'ID', 'CLOSE_SEXPR', 'CLOSE']);
+    shouldBeToken(result[1], "ID", "foo");
+    shouldBeToken(result[3], "ID", "bar");
+
+    result = tokenize("{{foo (a-x b-y)}}");
+    shouldMatchTokens(result, ['OPEN', 'ID', 'OPEN_SEXPR', 'ID', 'ID', 'CLOSE_SEXPR', 'CLOSE']);
+    shouldBeToken(result[1], "ID", "foo");
+    shouldBeToken(result[3], "ID", "a-x");
+    shouldBeToken(result[4], "ID", "b-y");
+  });
+
+  it('tokenizes nested subexpressions', function() {
+    var result = tokenize("{{foo (bar (lol rofl)) (baz)}}");
+    shouldMatchTokens(result, ['OPEN', 'ID', 'OPEN_SEXPR', 'ID', 'OPEN_SEXPR', 'ID', 'ID', 'CLOSE_SEXPR', 'CLOSE_SEXPR', 'OPEN_SEXPR', 'ID', 'CLOSE_SEXPR', 'CLOSE']);
+    shouldBeToken(result[3],  "ID", "bar");
+    shouldBeToken(result[5],  "ID", "lol");
+    shouldBeToken(result[6],  "ID", "rofl");
+    shouldBeToken(result[10], "ID", "baz");
+  });
+
+  it('tokenizes nested subexpressions: literals', function() {
+    var result = tokenize("{{foo (bar (lol true) false) (baz 1) (blah 'b') (blorg \"c\")}}");
+    shouldMatchTokens(result, ['OPEN', 'ID', 'OPEN_SEXPR', 'ID', 'OPEN_SEXPR', 'ID', 'BOOLEAN', 'CLOSE_SEXPR', 'BOOLEAN', 'CLOSE_SEXPR', 'OPEN_SEXPR', 'ID', 'INTEGER', 'CLOSE_SEXPR', 'OPEN_SEXPR', 'ID', 'STRING', 'CLOSE_SEXPR', 'OPEN_SEXPR', 'ID', 'STRING', 'CLOSE_SEXPR', 'CLOSE']);
+  });
 });
diff --git a/src/handlebars.l b/src/handlebars.l
index 913121c..996badb 100644
--- a/src/handlebars.l
+++ b/src/handlebars.l
@@ -12,8 +12,8 @@ function strip(start, end) {
 LEFT_STRIP    "~"
 RIGHT_STRIP   "~"
 
-LOOKAHEAD           [=~}\s\/.]
-LITERAL_LOOKAHEAD   [~}\s]
+LOOKAHEAD           [=~}\s\/.)]
+LITERAL_LOOKAHEAD   [~}\s)]
 
 /*
 ID is the inverse of control characters.
@@ -51,6 +51,9 @@ ID    [^\s!"#%-,\.\/;->@\[-\^`\{-~]+/{LOOKAHEAD}
 
 <com>[\s\S]*?"--}}"              strip(0,4); this.popState(); return 'COMMENT';
 
+<mu>"("                          return 'OPEN_SEXPR';
+<mu>")"                          return 'CLOSE_SEXPR';
+
 <mu>"{{"{LEFT_STRIP}?">"         return 'OPEN_PARTIAL';
 <mu>"{{"{LEFT_STRIP}?"#"         return 'OPEN_BLOCK';
 <mu>"{{"{LEFT_STRIP}?"/"         return 'OPEN_ENDBLOCK';
diff --git a/src/handlebars.yy b/src/handlebars.yy
index 63de17b..319b8ef 100644
--- a/src/handlebars.yy
+++ b/src/handlebars.yy
@@ -44,11 +44,11 @@ statement
   ;
 
 openBlock
-  : OPEN_BLOCK inMustache CLOSE -> new yy.MustacheNode($2[0], $2[1], $1, stripFlags($1, $3), @$)
+  : OPEN_BLOCK sexpr CLOSE -> new yy.MustacheNode($2, null, $1, stripFlags($1, $3), @$)
   ;
 
 openInverse
-  : OPEN_INVERSE inMustache CLOSE -> new yy.MustacheNode($2[0], $2[1], $1, stripFlags($1, $3), @$)
+  : OPEN_INVERSE sexpr CLOSE -> new yy.MustacheNode($2, null, $1, stripFlags($1, $3), @$)
   ;
 
 closeBlock
@@ -58,11 +58,10 @@ closeBlock
 mustache
   // Parsing out the '&' escape token at AST level saves ~500 bytes after min due to the removal of one parser node.
   // This also allows for handler unification as all mustache node instances can utilize the same handler
-  : OPEN inMustache CLOSE -> new yy.MustacheNode($2[0], $2[1], $1, stripFlags($1, $3), @$)
-  | OPEN_UNESCAPED inMustache CLOSE_UNESCAPED -> new yy.MustacheNode($2[0], $2[1], $1, stripFlags($1, $3), @$)
+  : OPEN sexpr CLOSE -> new yy.MustacheNode($2, null, $1, stripFlags($1, $3), @$)
+  | OPEN_UNESCAPED sexpr CLOSE_UNESCAPED -> new yy.MustacheNode($2, null, $1, stripFlags($1, $3), @$)
   ;
 
-
 partial
   : OPEN_PARTIAL partialName path? CLOSE -> new yy.PartialNode($2, $3, stripFlags($1, $4), @$)
   ;
@@ -71,9 +70,9 @@ simpleInverse
   : OPEN_INVERSE CLOSE -> stripFlags($1, $2)
   ;
 
-inMustache
-  : path param* hash? -> [[$1].concat($2), $3]
-  | dataName -> [[$1], null]
+sexpr
+  : path param* hash? -> new yy.SexprNode([$1].concat($2), $3)
+  | dataName -> new yy.SexprNode([$1], null)
   ;
 
 param
@@ -82,6 +81,7 @@ param
   | INTEGER -> new yy.IntegerNode($1, @$)
   | BOOLEAN -> new yy.BooleanNode($1, @$)
   | dataName -> $1
+  | OPEN_SEXPR sexpr CLOSE_SEXPR {$2.isHelper = true; $$ = $2;}
   ;
 
 hash