Scheme Interpreter


In the the course Software Engineering and Management and Design and implementation progressed programing languages at Stuttgart Media University, I developed an own Interpreter.


About the Interpreter

The syntax of this interpreter is based on the „lips“ family, a programming language which is structured in lists (definition). This type of programming language is very simple to understand and fast implemented. An element of a scheme list exist of two part the first is the „CAR“ – the value of the list and the second part is the „CDR“ the link to the “CAR” of the next list element. If the list element is the last in the list than the value of “CAR” is Null. For more Inforamtion have a look to dr. racket or the origin of car and cdr.


Projekt Setup

  • Programing language: C
  • Compiler: Clang
  • Environment: Eclipse CDT
  • Continues delivery: Jenkins
  • Version control: Git
  • Repository:



The project was developed with the test-driven development approach. Befor a function is implemented a test has to be written for it. This approach improves the quality of the code a lot comapre to just straitforward coding without a testing structure. Aswell it was used Jenkins for contunius delivery.  For this project only the standart “C” libiries where used. Therefore, played continues integration not a big role in this porject.


Develop Enviroment

All the code was developt in the Eclipse CDT envornment. This is an environment for C/C++, it includes all code “highliting” alswell as a debug function and compiling envornment. For this project the Clang compiler was used. Aswell it is possible to compile the project with the standart GCC compiler.


 Version control and continues delivery

Git was used for version control. The source code is hosted on the github server as a public project. To simplify the branches it is used two branches. A master and a develop branch. The active development take place on the develop branch. The continue delivery process was set up, that for every new git commit on the develop branch the build and deploy process in Jenkins was triggered. This was very easily set it up through the “GitHub hook trigger for GITScm polling” option in the project configuration in on the Jenkins server. When the build process was passed successful and Jenkins was able to execute the program than the Jenkins merged this stable commit to the origin master branch. With this simple process it was ensure that only a stable version of the program is on the master branch. As well I had Jenkins set up that I receive an email if the build is fail.


How to built execute a c project in Jenkins

This project was built with make. make is great tool with a simple syntax to describe the build steps of program. Because of the small size of this project it was enough to use one Makefile for the build description. The below code is a extract of the important part of the Makefile for this project. As you can see in with a very few lines or description a the hole program was build.

## Compiling files

OBJS=hbscheme.o hbscheme_test.o \

     reader.o memory.o \


## Clean up


        rm -f $(OBJS)

## include main header file to all files

$(OBJS): hbscheme.h

## Linking all object files togehter


        $(CC) $(DEBUG_FLAGS) -o $(APPLICATION) $(OBJS)

## run make with "make all"


To start this file also it needs only to cammands as you can see below.

# build hbScheme

make all

# run hbScheme


This shell script commands where set up the project configuration in Jenkins. Now the Jenkins server could run the Makefile, after pulling the project and compile build and execute the program.



Also in C, there are many ways to do testing. For this project I only us unit and function tests. As mentioned earlier this is a very small standalone program, also there is no GUI implemented in. Integration and GUI testing are not needed. I played around with quite some c test frameworks, but in the end I wrote my own test cases and let them run before start the program. But why I did not use a test framework. I had a closer look a googletest. This framework is written in C++ and used from many others to do unit testing for c project. But for me it was to complicate to test C code with a C++ framework. I set it up in the eclipse environment and there is runs OK. But I had big issues to get it run in my Jenkins set up. So I decided to write all the test cases in strait forward c function and execute it after the program init its environment so I can do beside the unit test also function tests. For me this was a very simple but efficient way of testing. If a test fail the program will stop and the error will be print out on the command line.

If it comes to Jenkins test report, ok this approach does not have a nice reporting like the xUnit plugin provides, but a simple print on the command line is enough for this size of program. When Jenkins is trying to build, and execute the program, the build process will fail if a test is failing. The reason where the test is failing is printed out on the command line, therefor I know where to debug. And if the build is failed there is also no merge to the master branch. So, there I had all the time a stable and executable version on the master branch is even the version on the develop branch is not. For sure the version on the master branch is only as stable as the test coverage. But with this problem every program should deal with. How to find the bug, which is outside the test range?

The below testfile shows a snipet of the console print after Jenkins build compile and run sucsessfull a version of the program.


clang    -o hbScheme hbscheme.o hbscheme_test.o reader.o memory.o utils.o
[hbScheme] $ /bin/sh -xe /var/folders/jt/r5k6nm0s74x547q27c824nym0000gn/T/
+ ./hbScheme

**** Start (UnitTest) ****
Done (a2l Test)
Done (Integer TAG and Check Test)
Done (True/False TAG Test)
Done (Symbol TAG Test)
**** Done (UnitTest) ****

**** Start (PerformanceTest)**** 
time to add 10000 new symbols: 650ms 
time to lookup 10000 existing symbols: 414ms
**** Done (PerformanceTest) ****

Welcome to our (incomplet) scheme

 > git tag -l jenkins-hbScheme-66 # timeout=10
 > git tag -a -f -m Jenkins Build #66 jenkins-hbScheme-66-SUCCESS # timeout=10
Pushing HEAD to branch master of origin repository
 > git --version # timeout=10
 > git push HEAD:master -f
Sending e-mails to:
Finished: SUCCESS

This snipet below shows a console print of a not sucessfuly build version. In line 13 is seen the output from the faild test case.


clang    -o hbScheme hbscheme.o hbscheme_test.o reader.o memory.o utils.o
[hbScheme] $ /bin/sh -xe /var/folders/jt/r5k6nm0s74x547q27c824nym0000gn/T/
+ ./hbScheme

**** Start (UnitTest) ****
hbscheme_test.c:37 assertion failed: a2l error/var/folders/jt/
r5k6nm0s74x547q27c824nym0000gn/T/ line 3: 21054 Abort trap: 6           ./hbScheme

Build step 'Shell ausführen' marked build as failure
Build did not succeed and the project is configured to only push after a 
successful build, so no pushing will occur.
Sending e-mails to:
Finished: FAILURE


Simple is better than complicated. I tried a lot with powerful test frameworks and blown up build processes. And in the end a small Makefile and simple test functions with no overhead test framework had brought me so far that I can continue to finish this this project will less effort. This was also my first time I used Jenkins. Even when the start was a bit rough. I think it is worthy even for a small project to set up this development process. Now I have all the time a very up to date stable version of the program. And because of the automation mechanism I do not have to spend time for it.



Hannes Buchwald (