Teaching 211 F '04 Assignments Set 1 Set 2 Set 3 Set 4 Set 5 Set 6 Set 7 Set 8 Set 9 Set 10 Set 11 Set 12 Set 13 Set 14

### Problem Set 4

Due date: 10/4 @ 6:00 pm

The goal is to understand data definitions for unions of data and self-referential data definitions.

HtDP Problems:

7.2.1, 7.2.2, 9.5.4, 9.5.6, 10.1.7

A railroad uses three kinds of trains to connect Aix-a-Chapelle with Fobyo:

1. `local`, which stops at all four train stations en route;
2. `regional`, which stops at Amy and Brian only;
3. `express`, which stops only at the destination.
All trains run every day. A train schedule for each kind of train consists of (1) the time when the train leaves Aix-a-Chapelle, (2) when it arrives at Fobyo, and (3) when it arrives at the intermediate stops, if any.

Your company supplies a software application for assisting the help desk clerks of this railroad company. Develop a data definition for the train schedules.

Develop a function that when given a train schedule and a time, determines whether the train arrives before the given time at its destination.

Develop a function that when given a list of Posns, creates a scene of 100 by 100 and places a solid yellow disk at each given Posn, if the coordinates of the Posn are between 0 and 100.

Develop the function `create-movie`, which when given a list of (positive) numbers, creates a list of that many solid red disks. The radius of the n-th solid disk is 10 times the n-th number in the given list. When you have developed the function, including tests, use the function `run-movie` to display the result of your function for some samples:
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