Begin Expression Arguments Rule

If Python is in the "begin_expr" state and the expression being evaluated is a function call, then prepend the function call arguments to the "Arguments" stack.

if the following are true:

  • expression state at time t = "begin_expr"
  • the expression at time t = function call with name: name and arguments: args

then arguments stack at time (t + 1) = [ args, arguments stack at time t ]

For example,

if the following are true:

  • expression state at time 1 = "begin_expr"
  • the expression at time 1 = __add__(5, 2)

then arguments stack at time (1 + 1) = [ [ 5, [ 2, [ ] ] ], arguments stack at time 1 ]


Notice that the list of arguments became 1 new element of the Arguments stack. Why didn't we just set the Arguments stack equal to the arguments list? If an argument (child) is also a function call, then the child has its own arguments (grandchildren). When it is time for the grandchildren to be added to the Arguments stack, they are added as a separate element to the stack. This way, the grandchildren are separated from the children. If there are more levels of descendents, more elements will be created in the Arguments stack.

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