Although programming using the CLI$ routines is not very hard, it would be nice if there were a code generator for the basic stuff based on the CLD file. Does anyone have something like that, or is there anyone interested in it?
There is a code generator of sorts at http://www.tomwade.eu/software/vmsarg.html
This is designed for when you're porting a C program onto VMS that is set up to use the typical terse and unfriendly qualifiers like
$ mumble -f -l foo.txt
that Unix loves. It generates code that allows the program to accept
$ mumble /fast /log=foo.txt
and translates it into the hieroglyphics that the program expects. Add CLD like functionality to the program with minimal C coding.
It sounds like you have used enough of the features of CLDs that it would be a project to write a TECO macro to massage the CLD into the corresponding MUMPS code. (Sorry, wrong language?) Even LIB$TPARSE, or its Alpha replacement, would take some time to wrangle. Sounds like you have a "boring job" ahead of you, or a co-op. (Named for the sound it makes when it hits the wall.) Or find a YACC guru or someone with facility at various other parsing tools and turn them loose.
Related
Simple question here, just can't seem to pass it google in a way it can understand.
Say I wanted to execute a line of actual programming code (c++ or java or python... etc) like SetCursorPos or printf from the command prompt command line. I vaguely imagine I would have to invoke the compiler and pass the command to it like a parameter, where from it would then be converted into machine language and passed to... where exactly?
Okay so that was kind of two questions.
How to run actual code from the command line and
what exactly is happening when a fully compiled program, or converted line of code (presuming these are essentially binary containers at that point), is executed?
Question one takes priority obviously. Unfortunately, I can not find any documentation on it, just a bunch of stuff vaguely related to it.
How to run actual code from the command line
Without delving into the vast amounts of blurriness between them, there are two major categories of language implementations: interpreters and compilers.
With many interpreters (or implementations with implicit compilation, such as V8 JavaScript's jit compiler, or pretty much anything with a repl), running a single line from the command line should be fairly trivial. CPython (the standard implementation of Python) has the -c command option:
$ python -c 'print("Hello, world!")'
Hello, world!
Language implementations with explicit compilation steps will tend to be decidedly less simple. In particular, the compiler would need to either accept source either from directly out of the argument list, or from standard input (via piping or redirection). On the output side, your compiler would have to support immediately executing that program, or outputting it to standard out, so that an operating system feature (if it exists) can execute it from a pipe.
To my knowledge, most explicit compilers are not designed with such usage in mind. In such cases, your best bet is to see if there is a REPL available for the language in question, preferably one as compatible with your compiler as possible, or to create (or find) a wrapper that makes it look like your language has a REPL. The wrapper would:
Accept input along the lines of CPython above.
Create a temporary source file behind the scenes with the code to be run and any necessary boilerplate.
Pass that file to the compiler.
Automatically run the resulting executable.
Delete the source file and executable. These may be cleaned up by the operating system later instead, if they're in a temp directory.
From the point of view of the user, this should look pretty similar to the CPython example, as they wouldn't have to interact with or see the compiler or temporary files.
I have a problem. I want to execute some commands in the Commandline of linux. I tested TProcess (So i am using Lazarus) but now when i am starting the programm, there is nothing, wich the Program do.
Here is my Code:
uses [...], unix, process;
[...]
var LE_Path: TLabeledEdit;
[...]
Pro1:=TProcess.Create(nil);
Pro1.CommandLine:=(('sudo open'+LE_Path.Text));
Pro1.Options := Pro1.Options; //Here i used Options before
Pro1.Execute;
With this Program, i want to open Files with sudo (The Programm is running on the User Interface)
->Sorry for my Bad English; Sorry for fails in the Question: I am using StackOverflow the first time.
I guess the solution was a missing space char?
Change
Pro1.CommandLine:=(('sudo open'+LE_Path.Text));
to
Pro1.CommandLine:=(('sudo open '+LE_Path.Text));
# ----------------------------^--- added this space char.
But if you're a beginner programmer, my other comments are still worth considering:
trying to use sudo in your first bit of code may be adding a whole extra set of problems. SO... Get something easier to work first, maybe
/bin/ls -l /path/to/some/dir/that/has/only/a/few/files.
find out how to print a statement that will be executed. This is the most basic form of debugging and any language should support that.
Your english communicated your problem well enough, and by including sample code and reasonable (not perfect) problem description "we" were able to help you. In general, a good question contains the fewest number of steps to re-create the problem. OR, if you're trying to manipulate data,
a. small sample input,
b. sample output from that same input
c. your "best" code you have tried
d. your current output
e. your thoughts about why it is not working
AND comments to indicate generally other things you have tried.
I am looking for a CVS equivalent to $id:$ in Accurev.
Before you start talking compile-time scripts - my major caveat is that a lot of my stuff is in Perl - so I can't do any of the normal "compile-time tricks" - as there really isn't much of any "compile-time" stuff.
I don't really want to require external files to define this stuff, as if (god forbid) the external definition files got out-of-sync with the actual scripts, etc...
I know I could always do some sort of compile-time preprocessor on the script files (to rewrite them) - but if there is a cleaner or better-integrated way of doing so (like "$id:$" I'd appreciate anyone ideas).
Before we get into more specifics, have you taken a look at the pre-keep trigger example AccuRev provides, addheader.pl?
You can find the example in the /AccuRev/examples/addheader.pl location.
Cheers,
~James
A computer scientist will correctly explain that all programs are
interpreted and that the only question is at what level. --perlfaq
How are all programs interpreted?
A Perl program is a text file read by the perl program which causes the perl program to follow a sequence of actions.
A Java program is a text file which has been converted into a series of byte codes which are then interpreted by the java program to follow a sequence of actions.
A C program is a text file which is converted via the C compiler into an assembly program which is converted into machine code by the assembler. The machine code is loaded into memory which causes the CPU to follow a sequence of actions.
The CPU is a jumble of transistors, resistors, and other electrical bits which is laid out by hardware engineers so that when electrical impulses are applied, it will follow a sequence of actions as governed by the laws of physics.
Physicists are currently working out what makes those rules and how they are interpreted.
Essentially, every computer program is interpreted by something else which converts it into something else which eventually gets translated into how the electrons in your local neighborhood fly around.
EDIT/ADDED: I know the above is a bit tongue-in-cheek, so let me add a slightly less goofy addition:
Interpreted languages are where you can go from a text file to something running on your computer in one simple step.
Compiled languages are where you have to take an extra step in the middle to convert the language text into machine- or byte-code.
The latter can easily be easily be converted into the former by a simple transformation:
Make a program called interpreted-c, which can take one or more C files and can run a program which doesn't take any arguments:
#!/bin/sh
MYEXEC=/tmp/myexec.$$
gcc -o $MYEXEC ${1+"$#"} && $MYEXEC
rm -f $MYEXEC
Now which definition does your C program fall into? Compare & contrast:
$ perl foo.pl
$ interpreted-c foo.c
Machine code is interpreted by the processor at runtime, given that the same machine code supplied to a processor of a certain arch (x86, PowerPC etc), should theoretically work the same regardless of the specific model's 'internal wiring'.
EDIT:
I forgot to mention that an arch may add new instructions for things like accessing new registers, in which case code written to use it won't work on older processors in the range. Much like when you try to use an old version of a library and then try to use capabilities only found in newer libraries.
Example: many Linux distros are released as 686 only, despite the fact it's in the 'x86 family'. This is due to the use of new instructions.
My first thought was too look inside the CPU — see below — but that's not right. The answer is much much simpler than that.
A high-level description of a CPU is:
1. execute the current op
2. grab the next op
3. goto 1
Compare it to Perl's interpreter:
while ((PL_op = op = op->op_ppaddr(aTHX))) {
}
(Yeah, that's the whole thing.)
There can be no doubt that the CPU is an interpreter.
It just goes to show how useless it is to classify something is interpreted or not.
Original answer:
Even at the CPU level, programs get rewritten into simpler instructions to allow the CPU to execute more them more quickly. This is done by changing the order in which they are executed and executing them in parallel. For example, Intel's Hyperthreading.
Even deeper, each instruction is considered a program of its own, one that routes electronic signals. See microcode.
The Levels of interpretions are really easy to explain:
2: Runtimelanguage (CLR, Java Runtime...) & Scriptlanguage (Python, Ruby...)
1: Assemblies
0: Binary Code
Edit: I changed the level of Scriptinglanguages to the same level of Runtimelanguages. Thank's for the hint. :-)
I can write a Game Boy interpreter that works similarly to how the Java Virtual Machine works, treating the z80 machine instructions as byte code. Assuming the original was written in C1, does that mean C suddenly became an interpreted language just because I used it like one?
From another angle, gcc can compile C into machine code for a number of different processors. There's no reason the target machine has to be the same as the machine you're compiling on. In fact, this is a common way to compile C code for AVRs and other microcontrollers.
As a matter of abstraction, the compiler's job is to translate flat text into a structure, then translate that structure into something that can be executed somewhere. Whatever is doing the execution may have its own levels of breaking out the structure before really executing it.
A lot of power becomes available once you start thinking along these lines.
A good book on this is Structure and Interpretation of Computer Programs. Even if you only get through the first chapter (or half of the first chapter), I think you'll learn a lot.
1 I think most Game Boy stuff was hand coded ASM, but the principle remains.
It is "common knowledge" that source filters are bad and should not be used in production code.
When answering a a similar, but more specific question I couldn't find any good references that explain clearly why filters are bad and when they can be safely used. I think now is time to create one.
Why are source filters bad?
When is it OK to use a source filter?
Why source filters are bad:
Nothing but perl can parse Perl. (Source filters are fragile.)
When a source filter breaks pretty much anything can happen. (They can introduce subtle and very hard to find bugs.)
Source filters can break tools that work with source code. (PPI, refactoring, static analysis, etc.)
Source filters are mutually exclusive. (You can't use more than one at a time -- unless you're psychotic).
When they're okay:
You're experimenting.
You're writing throw-away code.
Your name is Damian and you must be allowed to program in latin.
You're programming in Perl 6.
Only perl can parse Perl (see this example):
#result = (dothis $foo, $bar);
# Which of the following is it equivalent to?
#result = (dothis($foo), $bar);
#result = dothis($foo, $bar);
This kind of ambiguity makes it very hard to write source filters that always succeed and do the right thing. When things go wrong, debugging is awkward.
After crashing and burning a few times, I have developed the superstitious approach of never trying to write another source filter.
I do occasionally use Smart::Comments for debugging, though. When I do, I load the module on the command line:
$ perl -MSmart::Comments test.pl
so as to avoid any chance that it might remain enabled in production code.
See also: Perl Cannot Be Parsed: A Formal Proof
I don't like source filters because you can't tell what code is going to do just by reading it. Additionally, things that look like they aren't executable, such as comments, might magically be executable with the filter. You (or more likely your coworkers) could delete what you think isn't important and break things.
Having said that, if you are implementing your own little language that you want to turn into Perl, source filters might be the right tool. However, just don't call it Perl. :)
It's worth mentioning that Devel::Declare keywords (and starting with Perl 5.11.2, pluggable keywords) aren't source filters, and don't run afoul of the "only perl can parse Perl" problem. This is because they're run by the perl parser itself, they take what they need from the input, and then they return control to the very same parser.
For example, when you declare a method in MooseX::Declare like this:
method frob ($bubble, $bobble does coerce) {
... # complicated code
}
The word "method" invokes the method keyword parser, which uses its own grammar to get the method name and parse the method signature (which isn't Perl, but it doesn't need to be -- it just needs to be well-defined). Then it leaves perl to parse the method body as the body of a sub. Anything anywhere in your code that isn't between the word "method" and the end of a method signature doesn't get seen by the method parser at all, so it can't break your code, no matter how tricky you get.
The problem I see is the same problem you encounter with any C/C++ macro more complex than defining a constant: It degrades your ability to understand what the code is doing by looking at it, because you're not looking at the code that actually executes.
In theory, a source filter is no more dangerous than any other module, since you could easily write a module that redefines builtins or other constructs in "unexpected" ways. In practice however, it is quite hard to write a source filter in a way where you can prove that its not going to make a mistake. I tried my hand at writing a source filter that implements the perl6 feed operators in perl5 (Perl6::Feeds on cpan). You can take a look at the regular expressions to see the acrobatics required to simply figure out the boundaries of expression scope. While the filter works, and provides a test bed to experiment with feeds, I wouldn't consider using it in a production environment without many many more hours of testing.
Filter::Simple certainly comes in handy by dealing with 'the gory details of parsing quoted constructs', so I would be wary of any source filter that doesn't start there.
In all, it really depends on the filter you are using, and how broad a scope it tries to match against. If it is something simple like a c macro, then its "probably" ok, but if its something complicated then its a judgement call. I personally can't wait to play around with perl6's macro system. Finally lisp wont have anything on perl :-)
There is a nice example here that shows in what trouble you can get with source filters.
http://shadow.cat/blog/matt-s-trout/show-us-the-whole-code/
They used a module called Switch, which is based on source filters. And because of that, they were unable to find the source of an error message for days.