6.101Environment Diagram Questions
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Note that these questions do not affect your grade in 6.101 in any way!
They are presented here to provide some extra practice with environment
diagrams leading up to the first exam. If there are any bugs / issues with
this tool, please email 6.101-help and include a
description along with a screenshot of the issue.
Problem 0 - Diagramming Interface
In order to practice drawing environment diagrams, this question tasks you with using a drag-and-drop interface to construct a diagram.
The later questions on this page will ask you to develop diagrams on your own, but this question is designed to help you familiarize yourself with the interface itself.
Please use the interface below to re-create the following diagram. (note that the global frame has been provided)
1. Drag objects into the field to construct a diagram.
2. Use dots to create lines for variable bindings and pointers.
3. Don’t like a line? Redraw from the source dot to remove.
4. Don’t like an object? Move to trash.
5. Don't like arrow placement? Try moving objects around to redraw.
6. Add annotations if you'd like. They don't affect correctness.
Problem 1 - Function Definition
Create a diagram representing the result of executing the following code, consisting of a single function definition. Remember that a function object must contain the argument names, the function's body, and a pointer to the frame in which it was defined (its "enclosing frame").
def foo(n, k):
d = 2
return k/(n+k)
1. Drag objects into the field to construct a diagram.
2. Use dots to create lines for variable bindings and pointers.
3. Don’t like a line? Redraw from the source dot to remove.
4. Don’t like an object? Move to trash.
5. Don't like arrow placement? Try moving objects around to redraw.
6. Add annotations if you'd like. They don't affect correctness.
Problem 2 - Calling Functions
When calling a function, we follow several steps:
- Evaluate the function to be called, and its arguments (in order)
- Create a new frame for the function call, with the function's enclosing frame as its parent
- Bind the parameters of the function to the given arguments in this new frame
- Execute the body of the function in this new frame.
This process is demonstrated through the examples from the recitation 0 materials.
Note that in this interface, we specify each frame's parent with a line from
the dot at the top of each frame to its parent. Frames can also have a return
value. We will diagram the return value of the function using the return
pointer at the bottom of the frame. If the return pointer isn't set, this
corresponds to a function returning None.
Show/Hide Hints
- This diagram should have the global frame (the bordered one with the annotation of Global Frame) with variable
bar. - There should be a second frame according the function call with variable
xand thereturnpointer set to some object. - There should be 3 other objects: a function and two ints.
Using the interface below, diagram the state of the following program right
before the call to bar(2) finishes.
def bar(x):
return x**3
bar(2)
1. Drag objects into the field to construct a diagram.
2. Use dots to create lines for variable bindings and pointers.
3. Don’t like a line? Redraw from the source dot to remove.
4. Don’t like an object? Move to trash.
5. Don't like arrow placement? Try moving objects around to redraw.
6. Add annotations if you'd like. They don't affect correctness.
Problem 3 - Diagramming Function Calls
For this problem, diagram the result of executing the following code. Include
each of the frames generated by function calls. For this problem, there should
be three total frames: the global frame (already provided), one generated by a
call to foo and one generated by a call to bar.
def foo(y):
return bar(y+2)
def bar(x):
return x*3
foo(10)
1. Drag objects into the field to construct a diagram.
2. Use dots to create lines for variable bindings and pointers.
3. Don’t like a line? Redraw from the source dot to remove.
4. Don’t like an object? Move to trash.
5. Don't like arrow placement? Try moving objects around to redraw.
6. Add annotations if you'd like. They don't affect correctness.
Problem 4 - Nested Functions
This problem explores what happens when a function is defined inside of another
function. Use the interface below to diagram the state of the program just
before the call to add3(4) returns.
def outer(x):
def inner(y):
return x+y
return inner
add3 = outer(3)
add3(4)
Hint: for this problem, there should be three total frames: the global frame,
one generated by outer(3) and one generated by add3(4).
1. Drag objects into the field to construct a diagram.
2. Use dots to create lines for variable bindings and pointers.
3. Don’t like a line? Redraw from the source dot to remove.
4. Don’t like an object? Move to trash.
5. Don't like arrow placement? Try moving objects around to redraw.
6. Add annotations if you'd like. They don't affect correctness.
Problem 5 - Code to Generate a Diagram
Consider the following diagram:
In the box below, enter any valid Python program that, when executed, would lead to the diagram above.