SECTION(1, Tutorial 1)
m5_question(BO(Question 1.1: Installing TT(sjs-mode).) If you already
have GNU Emacs installed on your system, then here is how to install
the special TT(sjs-mode) or EM(Davin's Version of GNU Emacs): First
download a EM(tarball) (also known as a EM(compressed archive file))
from the following Web page:
m4_begin_center
TT(davinpearson.com/large-files-links.html)
m4_end_center
NU()and click on TT(dlisp.tar.gz), and unzip it to the folder pointed
to by the TT(HOME) environment variable. If this variable is unset,
as may be the case if you are using Microsoft Windows, then it should
be set to some sensible value (e.g. TT(c:/) or TT(c:/home)). It is
important that the value exists as a folder so that you can put your
code into that folder. To install just TT(sjs-mode) add the following
line of code to your TT(TILDE/.emacs) configuration file:
TT((load-file STRI("TILDE/dlisp/sjs-mode.el"))). To install Davin's
version of GNU Emacs including TT(sjs-mode) add the following line to
your TT(TILDE/.emacs): TT((load-file
STRI("TILDE/dlisp/d-start.el"))).)
m5_question(BO(Question 1.2: Some code to get you started.) You can
download a tarball from the above Web page and click on
TT(sjs-tutorials.tar.gz) containing the code you need to get started.
Then unzip the tarball to your TT(HOME) folder. Please note that
although these files are required to build S.J.S. code, you do not need
to look at these files unless you are a computer nerd and are curious
to know how my S.J.S. language works. For all of the questions that
follow this one, you should place your S.J.S. code in the folder
TT(sjs-tutorials) that was created when you unzipped the tarball.)
m5_question(BO(Question 1.3: Your first S.J.S. program.) Traditionally
in computer science the first program that you write in any programing
language is a program that does nothing else but prints out
TT("COMMA(Hello) World"). The following code does just that.
m4_ignore(In order to compile and run the following program you will
need use the EM(copy) feature of your web browser and the EM(paste)
feature of your text editor (which I hope for your sake is Davin's
version of GNU Emacs or GNU Emacs with Davin's TT(sjs-mode)) to bring
the following program code out of the S.J.S. web page and into your text
editor for editing purposes. Once you have copied and pasted your
code you can then compile and run it. Every other question in these
tutorial requires you to be familiar with the copy and paste operation
unless you are a masochist and like to type in your source code by
hand.) In the following code, note the use of the CLASS construct. In
Java and S.J.S., every piece of program code that does some real
computational work resides in a class of some description.
m4_begin_indent
NU()CLASS CLSS(MyFirstProgram) EOL
BEGIN EOL
PD BEGIN_MAIN EOL
PD PD SYSTEM_OUT_PRINTLN(STRI("COMMA(Hello) World!")); EOL
PD END_MAIN EOL
END EOL
m4_end_indent
NU()The code for any class CLSS(X) in these tutorials should reside in
a file called TT(X.sjs). Therefore the above code should be put into
a file called TT(MyFirstProgram.sjs). If two classes CLSS(X) and
CLSS(Y) use each other and CLSS(X) contains the MAIN function then it
is convenient to place them both in a file called TT(X.sjs). To build
and run some code[,] you first need to be in the TT(sjs-tutorials)
folder and secondly you need to issue the following shell command:
TT(make X.run) where TT(X) is the name of the class that you want to
run, so it is TT(make MyFirstProgram.run) in this case. For all
questions that follow this one, it will be assumed that you know how
to do this.)
m5_question(BO(Question 1.4: Multiple calls to
SYSTEM_OUT_PRINTLN.) Change the above code from printing the
string TT(STRI("[COMMA(Hello) World!]")) to printing out the following
messages. Please note that it will be easiest to use multiple calls
to SYSTEM_OUT_PRINTLN which sends text to the screen for the purpose
of viewing.
m4_begin_indent
NU()Hello, Anne! How are you doing? EOL
Hello, Brian! How are you doing? EOL
Hello, Clare! How are you doing? EOL
m4_end_indent
)
m5_question(BO(Question 1.5: Functions, parameters and
arguments.) A function is a piece of code that does some
computational work and optionally returns a value. Notice how the
TT(hello) function below takes a value of whose name to say hello to.
This value TT(who) is called a EM(parameter). The values passed to
the parameter by the call to the function is called an EM(argument).
For the purposes of this question, add two more calls to the TT(hello)
function in the MAIN function to get the same result as the code for
the previous question. The keyword EM(void) indicates that this
function does not return a value. See the next question for a
function that does return a value.
m4_begin_indent
NU()CLASS CLSS(Third) EOL
BEGIN EOL
PD FUNCTION VOID FUNC(hello)(STRING VARI(who)) EOL
PD BEGIN EOL
PD PD SYSTEM_OUT_PRINTLN(STRI("Hello ") + who + STRI("COMMA() how are you doing?")); EOL
PD END EOL
PD BEGIN_MAIN EOL
PD PD hello(STRI("Anne")); EOL
PD END_MAIN EOL
END EOL
m4_end_indent
)
m5_question(BO(Question 1.6: Return values.) Notice how the
following TT(hello) function returns a string rather than printing out
the string. Add two more calls to the TT(hello) function below to get
the same result as for Question QEST_MULTIPLE.
m4_begin_indent
NU()CLASS CLSS(Fourth) EOL
BEGIN EOL
PD FUNCTION STRING FUNC(hello)(STRING VARI(who)) EOL
PD BEGIN EOL
PD PD RETURN STRI("Hello ") + who + STRI("COMMA() how are you doing?"); EOL
PD END EOL
PD BEGIN_MAIN EOL
PD PD SYSTEM_OUT_PRINTLN(hello(STRI("Anne"))); EOL
PD END_MAIN EOL
END EOL
m4_end_indent
)
m5_question(BO(Question 1.7: Ignoring return values.) In Java
and S.J.S., it is not necessary to use a value that is returned by a
function. Sometimes this wastes computational resources since the
value that is computed by the function is not used but other times
when the function whose value is to be ignored does some additional
work by setting the value(s) of some variable(s) to different values
then the function call is not a waste of resources. To ignore the
value returned by the TT(hello) function, simply call the function
without using the value like so: TT(hello(STRI("Ignored"));) For the
purposes of this question, try calling the TT(hello) function without
using the return value by adding a line of code to the MAIN function.
)
m5_question(BO(Question 1.8: Comments.) Study the following code.
Note the use of COMM(TT(grey)) and SCOM(TT(red)) comments. Comments
are used to disable code for debugging purposes and also to help
explain how a program works. The most useful comment in S.J.S. and Java
is SCOM(TT(/**)) until the first SCOM(TT(*/)). This type of comment
is harvested by Javadoc to produce documentation on how a class works.
The second and third most useful comments are (respectively)
COMM(TT(//)) until the end of the line and COMM(TT(/*)) until the
first COMM(TT(*/)). The third type of comment is not very useful
because in Java you are not allowed to have one comment inside
another, so if you use this type of comment you will constantly need
to search for and remove COMM(TT(*/)) closing comments. In the
tutorials that follow you will see many comments, although mainly the
first and second types of comments.
m4_begin_indent
NU()SCOM(/** This comment is harvested by Javadoc EOL
PD PD to document the Fifth class */) EOL
CLASS CLSS(Fifth) EOL
BEGIN EOL
PD COMM(// I am a single line comment) EOL
PD COMM(/* I am EOL
PD PD PD a multi-line EOL
PD PD PD PD PD comment */) EOL
PD SCOM(/** This comment is harvested by Javadoc EOL
PD PD PD to document the hello function */) EOL
PD FUNCTION STRING FUNC(hello)(STRING VARI(who)) EOL
PD BEGIN EOL
PD PD RETURN STRI("Hello ") + who + STRI("COMMA() how are you doing?"); EOL
PD END EOL
PD SCOM(/** This comment is harvested by Javadoc EOL
PD PD PD to document the main function */) EOL
PD BEGIN_MAIN EOL
PD PD SYSTEM_OUT_PRINTLN(hello(STRI("Anne"))); EOL
PD END_MAIN EOL
END EOL
m4_end_indent
)
