Begin Expression Variable Rule

If Python is in the "begin_expr" state, at time t, and the current expression is variable x, then the "return value" is set to the value of x in the variables map.

if the following are true:

  • expression state at time t = "begin_expr"
  • the expression at time t = v
  • v is a variable

then Return Value at time (t + 1) = value at x in map (Variables Map at time t)

Whenever an expression has been evaluated, the result is stored in the "return value." For example,

if the following are true:

  • the expression at time 4 = x
  • expression state at time 4 = "begin_expr"
  • Variables Map at time 4 = [ entry x: 7, [ ] ]

then Return Value at time (4 + 1) = value at x in map (Variables Map at time 4)

We know that:

value at x in map [ entry x: 7, [ ] ] = 7

Therefore, we conclude that:

Return Value at time 5 = 7

See here for the full proof.

Try stepping through the simulator to see the "Return Value" set to the value of "x."

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