Problem 1: Interactive Scoping

• I am handing out folded sheets to each group. Focus initially on side A
• The idea is that each group is representing a stack frame
• You may want a scratch piece of paper out to track your variables
• When the global group tells me what would be printed, I will confirm if it is correct or not. If not, you’ll need to try again from the start.

Problem 1: Flow

• Things have been placed so that the group behind you is the one responsible for any functions you need to call
• That group’s function was defined in your group’s stack/function, but I just show you the header, not the contents
• When you need to call a function, you will need to tell the group behind you what values are assigned to each parameter
• When you return a value, you need to tell the group in front of you

Problem 1: Resolution

• Because each function is defined inside the preceding function, the immediate “enclosing” scope is the groups in front of you
• If you need to determine a value not defined in your stack frame, you need to send someone “up the stack” to find that value

Problem 2: Reversed Interactive Scoping

• Flip your folded sheet around now to side B
• The direction now is reversed, so that the group in front of you is who you call, and you return values to the group behind you
• Thus the group behind you is your immediate “enclosing” scope

Growing Trees