Extract |buildNodeVisitor|

src/checks.js

@@ -16,7 +16,7 @@ PEG.compiler.checks = [
       return function(node) { each(node[propertyName], check); };
     }
 
-    var checkFunctions = {
+    var check = buildNodeVisitor({
       grammar:
         function(node) {
           for (var name in node.rules) {
@@ -49,9 +49,7 @@ PEG.compiler.checks = [
       literal:      nop,
       any:          nop,
       "class":      nop
-    };
-
-    function check(node) { checkFunctions[node.type](node); }
+    });
 
     check(ast);
   },
@@ -64,7 +62,7 @@ PEG.compiler.checks = [
       check(node.expression, appliedRules);
     }
 
-    var checkFunctions = {
+    var check = buildNodeVisitor({
       grammar:
         function(node, appliedRules) {
           for (var name in node.rules) {
@@ -114,11 +112,7 @@ PEG.compiler.checks = [
       literal:      nop,
       any:          nop,
       "class":      nop
-    };
-
-    function check(node, appliedRules) {
-      checkFunctions[node.type](node, appliedRules);
-    }
+    });
 
     check(ast, []);
   }

src/emitter.js

@@ -90,7 +90,7 @@ PEG.compiler.emitter = function(ast) {
     }
   };
 
-  var emitFunctions = {
+  var emit = buildNodeVisitor({
     grammar: function(node) {
       var initializerCode = node.initializer !== null
         ? emit(node.initializer)
@@ -710,11 +710,7 @@ PEG.compiler.emitter = function(ast) {
         }
       );
     }
-  };
-
-  function emit(node, resultVar) {
-    return emitFunctions[node.type](node, resultVar);
-  }
+  });
 
   return emit(ast);
 };

src/passes.js

@@ -28,7 +28,7 @@ PEG.compiler.passes = [
         };
       }
 
-      var replaceFunctions = {
+      var replace = buildNodeVisitor({
         grammar:
           function(node, from, to) {
             for (var name in node.rules) {
@@ -59,11 +59,7 @@ PEG.compiler.passes = [
         literal:      nop,
         any:          nop,
         "class":      nop
-      };
-
-      function replace(node, from, to) {
-        replaceFunctions[node.type](node, from, to);
-      }
+      });
 
       replace(ast, from, to);
     }

src/utils.js

@@ -73,3 +73,15 @@ function quoteForRegexpClass(s) {
     .replace(/\u2029/g, '\\u2029') // paragraph separator
     .replace(/\n/g, '\\n')         // line feed
 }
+
+/*
+ * Builds a node visitor -- a function which takes a node and any number of
+ * other parameters, calls an appropriate function according to the node type,
+ * passes it all its parameters and returns its value. The functions for various
+ * node types are passed in a parameter to |buildNodeVisitor| as a hash.
+ */
+function buildNodeVisitor(functions) {
+  return function(node) {
+    functions[node.type].apply(null, arguments));
+  }
+}