Language Design Exercise: An Automated Testing Service

You are designing a software system for giving computer-based exams.
We want to define a language for describing exams and provide an
interpreter that will administer exams in that language through a text
interface.  Since this is an automated testing system, we want to
provide features such as skipping questions (if a student is doing
well on a topic) or printing progress reports (such as what percentage
of questions answered correctly) during the exam.

The language we design would be used by a teacher to write down an
exam that the interpreter would then give to a student.  The teacher
specifies (in the program) which questions to ask, when to skip
questions based on past results, when to print summaries of a
student's progress, and when to print other messages to the student.
Your system (interpreter) "runs" this program to administer the exam
to a student.

To help you get started, some sample interactions with the exam system
are provided below.  Your exam system should be able to
capture/administer both of these exams.

Review session students will work on the language design with Ethan on
Thursday and on the interpreter in class (with Kathi) on Friday.
Students who have stayed in Perrault will sketch out both parts of
this assignment during lecture on Friday.  

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Sample Exams

Here are sample sessions from giving two exams that a teacher might
want to program using your (one) language.

A WPI history exam

> (give-exam wpi-history)
When was WPI founded?
Ans: 1900
Let's see if you know your WPI personalities.
What is Gompei?
Ans [type hint for a hint]: hint
Think bleating
Ans: goat
Who was the first president of WPI?: (1) Boynton  (2) Washburn  (3)
Thompson
Ans: 1
You got 50% of the personalities questions right
Name one of the two towers behind a WPI education
Ans: boynton
You got 25% of the questions right
There's more WPI history on the web.  And life.

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A Math exam

Two different students took the same math exam.  The following two
examples show the students' interactions with the exam program.  Your
language should be sufficient to create one exam that could yield
these two different interactions based on students' answers.

Student #1

> (give-exam math-exam)
What is 3*4+2?
Ans: 14
What is 2+3*4?
Ans: 20
What is 5+2*6?
Ans: 42
You seem to be having trouble with order of operations.  Do the multiplication first.
What is 3+5*2?
Ans: 13
What is the reduced form of 12/18?: (1) 6/9  (2) 1/1.5  (3) 2/3
Ans: 3
What is 8+3*2?
Ans: 11
You got 40% of the arithmetic problems right
You got 100% of the fractions problems right

Student #2

> (give-exam math-exam)
What is 3*4+2?
Ans: 14
What is 2+3*4?
Ans: 14
What is 5+2*6?
Ans: 19
What is the reduced form of 12/18?: (1) 6/9  (2) 1/1.5  (3) 2/3
Ans: 3
What is 1/4 + 1/2?: (1) 3/4  (2) 1/6  (3) 2/6
Ans: 1
You got 66% of the arithmetic problems right
You got 100% of the fractions problems right