nl_tokens: Helper for creating visitors . Take an object of node name to handler mappings returns an object with a visit method that can be called
pl_tokens: function createVisitor ( handlers ) { nodeTypes . forEach ( function ( nodeType ) { if ( typeof handlers [ nodeType ] === 'undefined' ) { throw new Error ( 'No handler defined for ' + nodeType . displayName ) ; } } ) ; return { /**
       * Call the given handler for this node type
       * @param  {Object} node    the AST node
       * @param  {Object} context context to pass through to handlers
       * @return {Object}
       */ visit : function ( node , context ) { return this . handlers [ node . displayName ] . <mask> ( this , node , context ) ; } , handlers : handlers } ; }