DD2456 - Laboratory Exercise 2.
An Object Calculus (OC) Interpreter.
This exercise is designed
to deepen your understanding of the object calculus.
It will give you the chance to write and execute
simple object calculus programs.
1. Getting Started
You can develop an OC interpreter on any platform you wish, but consider that you
will have to demonstrate your interpreter to me personally. In the past I have found
that either a NADA Unix terminal or your own laptop in my office are the two
easiest methods to use.
1.1. The Interpreter Requirements
The requirements on the OC interpreter are as follows:
- The interpreter shall be able to read in an OC program (i.e. an OC term) as a string either
from the keyboard or from a named file.
The interpreter shall be able to parse the OC term. If the input term is syntactically well-formed
the interpreter shall construct a parse tree representation. If the input term is not
syntatically well-formed, the interpreter should return an appropriate error message
(such as "unmatched bracket"). The interpreter may return a pointer to where the error
lies in the term.
- If a parse tree can be successfully constructed for the input term, the user
shall be informed of this. Then the user shall be able to execute the OC term
by the method of "weak reduction". (See course notes). An OC program may
get into an infinite loop, and no method is practically possible to prevent this.
Otherwise the OC program will terminate under weak reduction.
If the OC program terminates under weak reduction, the interpreter will print out
the resulting parse tree in the form of a string. The output shall be printable
either to a named file, or to the screen. The interpreter will keep track of
how many individual reductions were made on the input term parse tree. On request,
the interpreter will display how many reductions were made.
It shall be possible for the end user to single-step through the reduction
of an OC term, applying just one weak reduction at each step. In this
case the interpreter will display the new form of the parse tree as a string
on the screen, after each individual reduction. This is to make debugging
of OC programs easier.
- The interpreter shall have an appropriate graphical user interface that makes
the various user activities easy to carry out.
The interpreter shall support the execution of type free lambda terms, either
directly using beta reduction, or else by translating them into OC terms and
executing them with OC weak reduction.
- The interpreter shall support the integer data type together with the successor
and addition, subtraction, and multiplication operations.
1.2. Evaluating your OC interpreter
While you are constructing the OC interpreter you should test it using the OC
program examples developed in class. When you are finished you shold develop
one OC program yourself to study OC reduction. One suggestion here is to
extend the desktop calculator program, but you can develop something similar.
Try to add some simple extra function, like a memory key (hint: consider object
backup in the course notes), or a new mathematical function.
1.3. Lab Demonstration
When you are happy with your work, and you have finished and debugged at least
one demo OC program, you should make an appointment with me for a demonstration.
You can e-mail me for this.
It is not necessary for the whole lab team to attend, but you must inform me
of all team members if I am to assign them marks. The demo will not take more
than about 10-15 minutes. To pass the demo, your program must:
(a) not crash, even on bad input,
(b) show that it satisfies all of the above "shall"
There is no deadline for this lab, but be aware of the deadlines
for LADOK points. Please do not wait until the last week of term and expect
that I will have time to see you then!