# STk stack window help

This window allows you to see the stack when an error occurs. Two sub-windows compose it.

- the topmost window (labeled Stack content) shows the contents of the stack when the error occurred. Each line contains the parameters passed to an invocation of the `eval` procedure (last call to eval is on the first line).
  This window is also made of two sub-windows.
  - On the left side is the environment in which the expression must be evaluated. Click on an item of this list to view the bindings defined in this environment.
  - On the right side, there is the expression to evaluate. Clicking on an item of this list sets the Listener default environment to the environment of this expression.
- the bottom window (labeled Listener) allows you to interact with the STk interpreter. The listener reads an expression in this window, evaluates it (in the environment previously selected in the above Stack window) and prints its result in this window.

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