Return State Rule

After a function has finished executing, Python returns to the line where the function was called (call site). The expression state is now set to "call_returned." More formally,

if the following are true:

  • the line at time t = i
  • the tab at time t = j
  • statement at line i, tab j = return rex
  • stack at time t = [ program context with variables: varis and expression state: (expression state with parent stack: parent_stack arguments: arg_stack values: value_stack line: line tab: tab) and control map: control_map, rest ]
  • expression state at time t = "end_expr"

then expression state at time (t + 1) = "call_returned"

For example,

if the following are true:

  • the line at time 26 = 3
  • the tab at time 26 = 1
  • statement at line 3, tab 1 = return z
  • stack at time 26 = [ program context with variables: [ entry a: 5, [ ] ] and expression state: (expression state with parent stack: [ ] arguments: [ ] values: [ ] line: 5 tab: 0) and control map: [ ], [ ] ]
  • expression state at time 26 = "end_expr"

then expression state at time (26 + 1) = "call_returned"

Try stepping through the simulator to see LW Python update the "Expression State."

Code Editor
LW Python State
Current Line1Current Tab0Time0
LW Python Simulator

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