References to objects in script

References to data objects and attributes

References to data objects in scripts are enclosed in square brackets:

The references are always relative to the base object. Every step describes the transition to the next object or value in the path.

A step may be

• A component name (symbol or string) or an attribute name (always symbol, see Options and attributes for list of attributes);
• A keyword (a symbol starting with :) or an expression #'name denoting a function to be applied to the previous object;
• A data object (or element of an array object) denoting the target of transition (the previous object is ignored);
• An integer denoting an index in an array object or in a list of objects;
• Symbol * denoting a slice of an array;
• An expression evaluated (with previous object as the base) to the target object. Note that the steps in a reference are already evaluated (with the script’s base). To prevent double evaluation either write it as 'step or (QUOTE step);
• If the previous object is a resource parameter (or its component with name model is a resource parameter) and the step cannot be applied to the previous object, it is applied to the referenced resource;
• If the previous object is an interface, the step may denote the name of the interface member (as defined in the interface type). For interfaces with single variable the step may also denote an attribute of that variable. The step :new extends an array interface and returns the new element.

A “data object” may be here

• An instance of a data object or an element of an array object (object index ...);
• A list of data objects. In this case
  • the “component” step either returns the named member of the list or (if there is no such member) is applied to every member and returns the list of results;
  • the “index” step treated as position in the list (starting with 1);
  • the “data” step returns that data;
  • all other types of steps are applied to every member of the list and return the list of results.
• A vector (not string). In this case
  • the “index” step treated as position in the vector (starting with 0);
  • the “data” step returns that data;
  • all other types of steps are applied to every element of the vector and return the vector of results.
• Any other value supports only “data” steps. Particularly, if the base object is NIL, any reference should start with a data object.

When a path is passed to a function, the interpretation of the path may be slightly different from the described procedure (we are trying to eliminate such differences).

Here is a list of useful keyword functions that may be used as steps in references (more functions are defined in applications):