NetRexx 1.128 NetRexx Installation and User's Guide
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Copyright(c) IBM Corporation, 1996, 1997. All rights reserved.
Introduction
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This document is the "User's Guide" for the reference implementation
of
NetRexx.
NetRexx is a new programming language; a blend of Rexx and Java; the
rules of syntax closely follow those of Rexx, while the semantics often
follow Java. It is a dialect of Rexx that is as efficient and portable
as Java, while preserving the philosophy and ease of use of Rexx.
This document covers:
o Unpacking the NetRexx packages
o Installing the NetRexx package -- documentation and samples
o Installing the NetRexx executables (for any Java platform):
o How to install the NetRexx compiler
o Problem solving
o How to install just the NetRexx runtime classes
o Using the NetRexxC compiler
o Using NetRexx classes with World Wide Web applets
o Installing and using the NetRexx print package
o Current restrictions, _etc._
The NetRexx documentation and software are distributed free of charge
under the conditions of the IBM Employee Written Software program.
If you download or use a NetRexx package you agree to the terms in the
_IBM License Agreement_ included in the package as the file license.txt.
For details of the NetRexx language, and the latest news, please see the
NetRexx documentation included with this package or available on the
World Wide Web, for example at: http://www2.hursley.ibm.com/netrexx/
Mike Cowlishaw
IBM UK Laboratories
Unpacking NetRexx packages
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The NetRexx packages are shipped in two forms, identified by a suffix
following the name:
o .zip format -- commonly used on OS/2 and other operating systems for
the IBM PC
o .tar.Z format -- (tape archive plus compress) commonly used on AIX
and other Unix systems.
You probably know how to handle these, but a word of caution: the
packages contain directory structures, and files with 'long names'
(that is, not of 8.3 maximum length names) which are case-sensitive.
Many utilities, including some versions of UNZIP and TAR, can lose
case information, truncate names, or fail to restore directories.
--- Unpacking .zip files ---
The most common packages for 'unzipping' these are Info-ZIP and PKZIP:
Here are some tips:
o Ensure that you are unzipping to a disk that supports long file
names (for example, an HPFS disk or equivalent on OS/2 or Windows).
o Info-ZIP: use version 5.12 (August 1994) or later. The syntax for
unzipping NetRexx.zip is simply
unzip NetRexx
which should create the files and directory structure directly.
Please see later in this document for complete installation
instructions.
o PKZIP: use a version that supports long file names. The syntax for
unzipping NetRexx.zip is
pkunzip -d NetRexx
which should create the files and directory structure directly. The
'-d' flag indicates that directory structure should be preserved.
--- Unpacking .tar.Z files ---
You need an up-to-date version of two programs: 'tar' and 'uncompress';
these are available for most operating systems. Here are some tips:
o Ensure that you are unpacking to a disk that supports long file
names (for example, any Unix disk, or an HPFS disk or equivalent on
OS/2 or Windows).
o Ensure that the version of tar that you use preserves case in names.
If all the files created by tar have all-lowercase names, you need a
new version of tar.
The process of unpacking the file takes two steps:
1. Uncompress the file, using uncompress (this may be called
simply 'compress' on some systems). The syntax for uncompressing
NetRexx.tar.Z is probably one of:
(the '-d' means decompress, and may be optional). This should
replace the file with one called NetRexx.tar
2. Unpack the files and directories from the .tar file. The syntax
for this is
tar -xvf NetRexx.tar
This should create the files and directories from the package,
displaying the name of each as it is unpacked. You may see error
messages where directories already exist; these can be ignored.
After unpacking the files, the .tar file can be erased.
Installation procedure - online documentation and samples
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The NetRexx package (NetRexx.zip, or NetRexx.tar.Z) contains the NetRexx
online documentation, together with samples and examples, and the
packages of executables.
1. Copy the package file to the root directory of your choice,
preserving the original name.
2. With your chosen directory as your current directory, unpack the
package, following the instructions in 'Unpacking NetRexx packages'
above.
This should add the directory 'NetRexx' to your chosen directory,
containing the documentation and samples for NetRexx, along with
the packages of executables. There should also be a subdirectory
('NetRexx/netrexx/lang' or 'NetRexx\netrexx\lang') containing runtime
class files used by some of the samples.
The online documentation comes in two forms: plain ASCII (files with
extension '.doc'), and World Wide Web hypertext format (files with
extension '.htm' or '.html', '.gif', etc.). To view the hypertext
version, start your browser at the file "netrexx.htm". For example,
if
you are using the IBM Web Explorer then the command
explore netrexx.htm
(executed when the documentation directory is the current directory)
should show the NetRexx front page.
Included in the documentation collection are a number of examples and
samples (Hello, HelloApplet, etc.). To run any of these, you must have
the Java runtime environment installed.
Some of the examples must be viewed using the Java toolkit applet-viewer
or a Java-enabled browser. Please see the hypertext pages describing
these for detailed instructions. In general, if you see a message from
Java saying:
void main(String argv[]) is not defined
this means that the class cannot be run using just the 'java' command.
Installation of NetRexx Executables
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The NetRexx package includes two packages of software (each will have
the same suffix as the package you unpacked it from, that is, '.zip' or
'.tar.Z'):
1. nrtools -- the files for the NetRexx compiler, of which the most
important is NetRexxC.zip, which contains the Java .class files
that implement the compiler. The NetRexx compiler is in fact a
translator; it translates NetRexx programs to Java source code,
which is then compiled using the javac compiler (or you can use the
Java compiler of your choice, if you prefer). This package
requires that the Java toolkit (1.1.0 or later) be installed.
nrtools also includes a separate copy of the NetRexx runtime
classes, in NetRexxR.zip
2. nrping -- the Pinger sample application. Please see Pinger.htm for
information about this.
To install and use either of these packages, you must have already
installed the Java Development Kit (JDK) runtime (and toolkit, if you
want to compile NetRexx programs). For more information on these:
o For OS/2 and AIX and other IBM operating systems, see the _IBM
Centre for Java Technology_ page at:
http://ncc.hursley.ibm.com/javainfo/hurindex.html
o For other operating systems, see the _Sun Microsystems Java_ page
at http://www.javasoft.com, or other suppliers of Java toolkits.
Installation of the NetRexx compiler
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Here's how to install the NetRexx compiler and runtime classes. These
instructions apply to the majority of Java platforms (for use with
Visual J++, please see below).
1. Copy the 'nrtools.zip' or 'nrtools.tar.Z' file from the NetRexx
documentation directory to the Java home directory, using the
original name. The name of the Java home directory will vary
depending on the operating system you are using. Some
possibilities are:
/java
\java11
\jdk1.1
It will contain directories such as 'bin' and 'lib'.
[Note: if your Java home directory is on a CD-ROM, or otherwise
inaccessible, you'll need to choose a different directory and set
up a CLASSPATH environment variable that points to it. Consult
your Java toolkit documentation for details on how to do this.]
2. With the Java home directory as your current directory, unpack the
package, following the instructions in "Unpacking NetRexx packages"
above.
This should add the .zip files for the NetRexx runtime and compiler
classes (NetRexxR.zip and NetRexxC.zip) to the Java 'lib' directory.
In addition, some sample scripts and a test program should have
been added to the Java 'bin' directory:
hello.nrx -- a simple NetRexx program for testing
NetRexxC.cmd -- the NetRexx compiler command in Rexx
NetRexxC.bat -- similar NetRexx compiler command (Windows .bat)
nrc.cmd -- shorter name for NetRexxC.cmd
nrc.bat -- shorter name for NetRexxC.bat
The .cmd files are simple Rexx scripts for making it easier to use
the compiler. You don't have to use these, but they save some
typing. They should require little modification to run under
the Rexx interpreter for your platform; for details of Rexx
interpreters, see: http://www2.hursley.ibm.com/rexx/
Under Windows, the .bat files should serve the same purpose -- they
are not as flexible as the Rexx .cmd files, but will save typing.
3. Check that the names are correct in the 'lib' directory: there
should be a file in the directory called 'NetRexxC.zip'; if
the name is all in upercase or all in lowercase the package has not
been unpacked correctly (see "Unpacking NetRexx packages").
4. For Java to be able to find the NetRexx classes, you must update
the CLASSPATH environment variable by adding the full path and name
of the NetRexxC.zip file to the CLASSPATH setting. There will
often already be a CLASSPATH variable set, including a path to the
standard Java classes.zip file. Specify or add the full path
(disk, directories, and file specification) for NetRexxC.zip,
making sure that the case of every letter is exactly right (Java is
very case-sensitive). For example, the full path might be something
like:
e:\java11\lib\NetRexxC.zip
The procedure for setting the CLASSPATH variable depends on your
operating system (and there may be more than one way). Here are
some examples:
o In OS/2 or Windows, use a SET CLASSPATH= command in CONFIG.SYS
(for OS/2) or in AUTOEXEC.BAT (for Windows) and re-boot after
changing. In both cases the command syntax is the same, and
might look like this:
set classpath=.;f:\javaos2\lib\NetRexxC.zip
In this example, the first segment of the value (before the
semicolon) lets classes in the current directory be found, and
the second segment includes the classes needed by NetRexx.
Both environments normally include the standard Java classes
automatically.
Under Windows NT 4.0 the CLASSPATH can be set using Start,
Settings, Control Panel, System, Environment tab, System
Variables, and clicking on CLASSPATH.
o For Unix (Korn shell or Bourne shell), use:
CLASSPATH=<newdir>:$CLASSPATH
export CLASSPATH
and changes for re-boot or opening of a new window should be
placed in your .login (Bourne) or .profile (Korn) file
o For Unix (C shell), use:
setenv CLASSPATH <newdir>:$CLASSPATH
and changes for re-boot or opening of a new window should be
placed in your .cshrc file
If you are unsure of how to do this, check the documentation you
have for installing the Java toolkit.
Note: If you add NetRexxC.zip to the CLASSPATH value then you do not
need to add NetRexxR.zip; the latter contains only the NetRexx runtime
classes (which are provided separately for people who don't want to run
the NetRexx compiler). These runtime classes are also included in
NetRexxC.zip. Whichever zip is used, the NetRexx runtime classes can be
referred to from Java or NetRexx as being in the 'netrexx.lang' package.
For example, a string might be of class 'netrexx.lang.Rexx'.
--- Checking your installation is correct ---
To check installation, change directory to the Java 'bin' directory,
then (being very careful to get the case of letters correct):
o Enter the command
java COM.ibm.netrexx.process.NetRexxC hello
This should run the NetRexx compiler, which converts the NetRexx
program 'hello.nrx' to the Java program 'hello.java'. It then
invokes the default Java compiler (javac), to compile the file
'hello.java' to make 'hello.class'. The intermediate .java file
is then deleted, unless an error occurred.
o Enter the command
java hello
This runs (interprets bytecodes from) the 'hello.class' file,
which should display a simple greeting. On some systems, you may
first have to add the directory that contains the 'hello.class'
file to the CLASSPATH setting (see above) so Java can find it.
With the sample scripts provided (NetRexxC.cmd or NetRexxC.bat), or the
equivalent in the scripting language of your choice, the steps above can
be combined into a simple single command:
NetRexxC -run hello
This package also includes a trivial 'nrc.cmd' and matching 'nrc.bat'
file that simply passes on its arguments to NetRexxC; 'nrc' is just a
shorter name that saves keystrokes, so for the last example you could
type:
nrc -run hello
Note that scripts may be case-sensitive; unless running the OS/2 Rexx
script, you will probably have to spell the name of the program exactly
as it appears in the filename.
You could also edit the nrc.cmd or nrc.bat and add your favourite
'default' NetRexxC options there (if you do this, keep a backup copy, so
that if you install a new version of the NetRexx package you won't
overwrite your changes).
--- Installing NetRexx for use with Visual J++ ---
(Many thanks to Bill Potvin and Bernhard Hurzeler for the details in
this and the following section.)
1. Copy the following file into the [java_root]\Lib directory:
NetRexxC.zip
For example, if [java_root] is "E:\Java":
C:\>copy NetRexxC.zip E:\Java\Lib
2. Similarly, copy the nrc.bat and NetRexxC.bat files to the
[java_root]\Bin directory.
Under Windows NT 4.0 this can be done using Start, Settings,
Control Panel, System, Environment tab, System Variables, and
clicking on CLASSPATH.
--- Using NetRexx with Visual J++ ---
1. Use the J++ "jview" command to invoke the NetRexx translator to
convert a NetRexx program (e.g., hello.nrx) into a Java program
(hello.java). You must specify the "-nocompile" option to NetRexx
in order to prevent it from trying to invoke the Java toolkit
compiler (which isn't in the MicroSoft J++ classes).
For example, if hello.nrx is in the current directory:
The result of this step should be a Java source file called
"hello.java".
2. Use the J++ "jvc" command to compile the Java source file:
jvc hello.java
The result of this step should be a Java .class file called
"hello.class".
3. Execute the class file with the J++ command "jview":
jview hello
Note that all the commands above probably have to be typed exactly as
shown (Java is very case-sensitive). The supplied NetRexxC.bat can be
modified to work with the above commands by using 'jview' instead of the
'java' command and adding the 'jvc' step.
Problems?
'''''''''
If the 'hello' example doesn't work, one of the following problems
may be the cause:
o A "Can't find class COM.ibm.netrexx.process.NetRexxC..." message
probably means that the NetRexxC.zip file has not been specified in
your CLASSPATH setting, or is misspelled, or is in the wrong case.
The CLASSPATH is the setting that Java uses to find classes for
execution; please refer to your Java installation instructions for
information on setting the CLASSPATH.
o A "Can't find class hello..." message may mean that the directory
with the hello.class file is not in your CLASSPATH, or either the
filename or name of the class (in the source) is spelled wrong (the
java command is [very] case-sensitive).
o You didn't install on a file system that supports long file
names (for example, on OS/2 or Windows you should use an HPFS disk
or equivalent). Like most Java applications, NetRexx uses long file
names.
o You have a down-level Unzip or Tar program. Check that the
file 'NetRexxC.zip', with just three capital letters, exists in the
subdirectory 'lib' below the Java home directory.
o You have only the Java runtime installed, and not the toolkit. If
the toolkit is installed, you should have a program called javac
on your computer.
o You have a down-level version of Java installed. NetRexxC 1.1xx
will run only on Java version 1.1.0 (and later versions). You can
check the version of Java you have installed using the command 'java
-version'. An older version of the NetRexx package is available for
Java 1.0, however that version will no longer be enhanced or
supported in any way.
o Your Java toolkit installation has .class files from an earlier
installation of NetRexx in classes/java/lang, classes/netrexx/lang,
or other subdirectories in the 'classes' directory below the Java
home directory.
A message that reports ambiguous class references is a likely sign
of this problem. The easiest way to solve it is to re-install the
Java toolkit in a clean subdirectory.
o An 'Out of environment space' message when trying to set CLASSPATH
under Win95-DOS can be remedied by adding /e:4000 to the 'Cmd line'
entry for the MS-DOS prompt properties (try 'command /?' for more
information).
o If, when reporting an error or warning, the compiler gives a rather
cryptic identifier and reports 'Sorry, full message not available',
this means that it could not find the NetRexxC.properties (error
messages) file, which should be in the COM.ibm.netrexx.process
package (in NetRexxC.zip).
o An 'Exception 0005' when using the OS/2 beta Java 1.1.1 toolkit is
probably caused by the just-in-time compiler. Try turning it off
before running NetRexxC by setting the environment variable:
SET JAVA_COMPILER=no
(and ignore the 'unable to load dll' message).
o An ArrayIndexOutOfBoundsException when compiling hello.nrx under AIX
is caused by an early faulty JIT. Either disable the JIT (as for
OS/2) or update your AIX Java SDK.
Installation of just the NetRexx classes
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To install only the NetRexx runtime classes (you don't need to do this
if you already installed the NetRexxC compiler), follow the instructions
for installing the compiler, but set your CLASSPATH to refer to
NetRexxR.zip instead of NetRexxC.zip. Only the NetRexxR.zip is needed,
so you may prefer to extract just this file from the nrtools package.
The NetRexx class files can then be referred to from Java or NetRexx
programs as from package 'netrexx.lang'. For example, a string might be
of class 'netrexx.lang.Rexx'.
Using the NetRexx compiler
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The installation instructions for the NetRexx compiler describe how to
use the package you installed to compile and run a simple NetRexx
program. This section explains more of the options available to you.
--- Invoking the compiler as a command ---
The compiler is a Java program (class) which is called
COM.ibm.netrexx.process.NetRexxC (NetRexxC for short). This can be
invoked using the Java interpreter, for example, by the command:
java COM.ibm.netrexx.process.NetRexxC
or by using a system-specific command (such as 'NetRexxC' or 'nrc'). In
either case, the compiler invocation is followed by one or more file
specifications (these are the names of the files containing the NetRexx
source code for the programs to be compiled).
File specifications may include a path; if no path is given then
NetRexxC will look in the current (working) directory for the file.
NetRexxC will add the extension '.nrx' to input program names (file
specifications) if no extension was given.
So, for example, to compile 'hello.nrx' in the current directory, you
can use any of:
(the first two should always work, the last two require that the
system-specific command be available). The resulting .class file is
placed in the current directory, and the .crossref (cross-reference)
file is placed in the same directory as the source file (if there are
any variables and the compilation has no errors).
Here's an example of compiling two programs, one of which is in the
directory 'D:\myprograms':
nrc hello d:\myprograms\test2.nrx
In this case, again, the .class file is placed in the current directory.
Note that when more than one program is specified, they are all compiled
with the same class context: that is, they can 'see' the classes,
properties, and methods of the other programs being compiled, much as
though they were all in one file. This allows mutually interdependent
programs and classes to be compiled in a single operation (but see the
section "Compiling multiple programs" below, if you use the PACKAGE
instruction).
The programs do, however, maintain their independence (that is, they may
have different options, import, and package instructions).
On completion, the NetRexxC command will exit with one of three return
values: 0 if the compilation of all programs was successful, 1 if there
were one or more Warnings, but no errors, and 2 if there were one or
more Errors.
As well as file names, you can also specify various option words, which
are distinguished by the first character of the word being '-'. These
may be any of the option words allowed on the NetRexx OPTIONS
instruction (see the NetRexx language documentation), prefixed with '-'.
These options words can be freely mixed with file specifications.
The compiler also implements some additional option words, which cannot
be used on the OPTIONS instruction:
o -keep keep the intermediate .java file for each program. It
is kept in the same directory as the NetRexx source file
as xxx.java.keep, where xxx is the source file name.
The file will also be kept automatically if the javac
compilation fails for any reason.
o -nocompile do not compile (just translate). Use this option when
you want to use a different Java compiler. The .java
file for each program is kept in the same directory as
the NetRexx source file, as the file xxx.java (where xxx
is the source file name); any -keep option is ignored.
o -time display translation, javac compile, and total times (for
the sum of all programs processed).
If you are using the provided NetRexxC or nrc scripts, then an
additional option is available:
o -run run the resulting JAVA class as a stand-alone
application, provided that the compilation had no
errors.
Option words may be specified in lowercase, mixed case, or uppercase.
File specifications are platform-dependent and may be case sensitive,
though NetRexxC will always prefer an exact case match over a mismatch.
Note that the -run option is implemented by the script, not the
compiler; some scripts (such as NetRexxC.bat) may require that the
'-run' be the first word of the command arguments, and/or be in
lowercase. They may also require that only the name of the file be
given if the -run option is used.
See also the earlier section "The NetRexx home directory" if you need
to
change the place where the compiler finds its messages (for example, if
error messages report 'Sorry, full message unavailable').
--- Compiling multiple programs ---
When you specify more than one program for NetRexxC to compile, they are
all compiled with the same class context: that is, they can 'see' the
classes, properties, and methods of the other programs being compiled,
much as though they were all in one file.
This allows mutually interdependent programs and classes to be compiled
in a single operation. For example, consider the following two programs
(assumed in your current directory, as the files X.nrx and Y.nrx):
/* X.nrx */
class X
why=Y null
/* Y.nrx */
class Y
exe=X null
each contains a reference to the other, so neither can be compiled in
isolation. However, if you compile them together, using the command:
nrc X Y
then the cross-references will be resolved correctly. The total elapsed
time will be less, too, as the class files used by the NetRexxC compiler
or the programs themselves will only be loaded once.
This example works as you would expect for programs that are not in
packages. There's a restriction, though, if the classes you are
compiling _are_ in packages (that is, they include a PACKAGE
instruction). Currently, NetRexxC uses the javac compiler to generate
the .class files, and for mutually-dependent files like these, javac
requires that the source files be in the Java CLASSPATH, in the
sub-directory described by the PACKAGE instruction.
So, for example, if your project is based on the tree:
D:\myproject
then if the two programs above specified a package, thus:
/* X.nrx */
package foo.bar
class X
why=Y null
/* Y.nrx */
package foo.bar
class Y
exe=X null
then:
1. You should put these source files in the directory: D:\myproject\foo\bar
2. The directory D:\myproject should appear in your CLASSPATH setting
(if you don't do this, javac will complain that it cannot find one
or other of the classes).
3. You should then make the current directory be D:\myproject\foo\bar
and then compile the programs using the command 'nrc X Y', as
above.
With this procedure, you should end up with the .class files in the same
directory as the .nrx files, and therefore also on the CLASSPATH and
immediately usable by other packages.
Note that when javac is used to generate the .class files, no new .class
files will be created if any of the programs being compiled together had
errors.
Note also that if class is abstract or is an adapter class then it
should be placed in the list before any classes that extend it (as
otherwise any automatically generated methods will not be visible to the
subclasses).
--- Invoking the compiler from Java ---
The compiler may be called from a Java program directly, by invoking the
method in the COM.ibm.netrexx.process.NetRexxC class described as
follows:
method main(arg=Rexx) constant returns int
The Rexx string passed to the method can be any combination of program
names and options (except -run), as described above. A sample NetRexx
program that invokes the NetRexx compiler to compile a program called
'test' is:
/* compiletest.nrx */
s='test -keep -verbose4 -utf8'
say COM.ibm.netrexx.process.NetRexxC.main(s)
The returned int value will be one of the return values described above.
NetRexxC is thread-safe (the only static properties are constants), but
it is not known whether javac is thread-safe. Hence the invocation of
multiple instances of NetRexxC on different threads should probably
specify -nocompile, for safety.
NetRexx classes and Applets for the Web
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If you write applets for the World Wide Web (or your intranet) in
NetRexx, you will probably need to use the NetRexx classes
(netrexx.lang.Rexx, _etc._); they will be used automatically if the
default compilation options (specifically, options nobinary) are in
effect.
A good way of setting up an HTTP (Web) server for this is to keep all
your applets in one subdirectory; you can then make the NetRexx runtime
classes (that is, the classes in the package known by Java as
netrexx.lang) available to all the applets by unzipping NetRexxR.zip
into a subdirectory netrexx/lang below your applets directory.
For example, if the root of your server tree is
D:/mydata
then you might put your applets into
D:/mydata/applets
and then the NetRexx classes (unzipped from NetRexxR.zip) should be in
the directory
D:/mydata/applets/netrexx/lang
The same principle is applied if you have any other Java packages that
you want to make available to your applets: the classes in a package
called fred.math.quicksorts would go in a subdirectory below applets
called fred/math/quicksorts, for example.
Note that with Java 1.1 it should be possible to use the classes direct
from the NetRexxR.zip file (which is in fact a Java 'jar' file),
providing that the browser being used is at a Java 1.1 level. See the
Java 1.1 documentation for details.
Printable documentation
"""""""""""""""""""""""
The NetRexx printable package (NetRexxD.zip, or NetRexxD.tar.Z) contains
the printable NetRexx documentation, in PostScript format.
1. Copy the package file to the root directory of your choice for
documentation, preserving the original name.
2. With your chosen directory as your current directory, unpack the
package, following the instructions in 'Unpacking NetRexx packages'
above.
This should add the directory 'NetRexxD' to your chosen directory,
containing the printable documentation for NetRexx.
3. You can print files from the new directory that have the extension
'.ps' on any PostScript printer, using the appropriate method for
printing for your operating system. There are also utilities, such
as 'GhostScript', available from public sources for viewing
PostScript files and for printing them on non-PostScript printers.
Current restrictions
""""""""""""""""""""
The NetRexx processor is now functionally complete, though work
continues on usability and performance improvements. As of this version
there are still a number of restrictions, listed below.
Please note that the presence of an item in this section is not a
commitment to remove a restriction in some future update; NetRexx
enhancements are dependent on on-going research, your feedback, and
available resources. You should treat this list as a 'wish-list' (and
please send in your wishes).
--- Short-term restrictions ---
The following problem may occur in larger methods, with Java 1.0.1,
1.0.2, or 1.1.1 (it may have been fixed in later versions):
o NetRexxC does not restrict the number of local variables used or
generated. However, the 1.0 javac compiler fails with unrelated
error messages (such as 'statement unreachable' or 'variable may be
uninitialized') if asked to handle more than 63 local variables.
--- Long term restrictions ---
The following restrictions are due to the use of a translator, and would
probably only be lifted if a direct-to-bytecodes NetRexx compiler were
built.
o Externally-visible names (property, method, and class names) cannot
be Java reserved words (you probably want to avoid these anyway).
o There are various restrictions on naming and the contents of
programs (the first class name must match the program name, etc.).
o The javac compiler requires that mutually-dependent source files be
on the CLASSPATH, so javac can find the source files. NetRexxC does
not have this restriction, but when using javac for the final
compilation you will need to follow the convention described under
'Compiling multiple programs', above.
o The 'symbols' option applies to all programs compiled together if
any of them specify that option.
o Some binary floating point underflows may be treated as zero instead
of being trapped as errors.
o Side-effects of calls to this() and super() in constructors may be
seen before the method and method call instructions are traced --
this is because Java does not permit tracing instructions to be
added before the call to this() or super().
o The results of expressions consisting of the single term 'null' are
not traced.
