# Tracing Joy Execution

## `joy.utils.pretty_print`

Pretty printing support, e.g.:

    Joy? 23 18 * 99 +
           . 23 18 mul 99 add
        23 . 18 mul 99 add
     23 18 . mul 99 add
       414 . 99 add
    414 99 . add
       513 .

    513 <-top

    joy?

On each line the stack is printed with the top to the right, then a `.` to represent the current locus of processing, then the pending expression to the left.

class `joy.utils.pretty_print.``TracePrinter`

  This is what does the formatting. You instantiate it and pass the `viewer()` method to the `joy.joy.joy()` function, then print it to see the trace.

  `go`()

    Return a list of strings, one for each entry in the history, prefixed with enough spaces to align all the interpreter dots.

    This method is called internally by the `__str__()` method.

    Return type: | list(str)

  `viewer`(stack, expression)

    Record the current stack and expression in the TracePrinter’s history. Pass this method as the `viewer` argument to the `joy.joy.joy()` function.

    Parameters:

    - quote (stack) – A stack.
    - expression (stack) – A stack.