NB: This question is more about how to navigate through/decipher OCaml source code, than about the specifics of the items listed below.1
I've come across the expressions
`Malformed
`Uchar
in some OCaml source code, but I can't find definitions for them.
Are they somehow built-in, i.e. part of the standard language?
If not, where does one go when one wants to find out such definitions? (Actually, it's not clear to me whether the leading backtick is part of the name or is a separate operator.)
1I'm having a horrible time making sense of OCaml source code. Usually I have no problem picking up new programming languages, but with OCaml I can't find anything where I expect to find it, and when I do find something it comes along with 100x more undefined/differently-defined/outright bizarre names/concepts, so it's a losing battle.
It's a polymorphic variant, you can read about it in the OCaml manual here
For other basic language features you would not understand, well, you should first read the whole part 1 of the manual
Here is how the manual is organized:
Quick introduction through the language
The whole language (two parts: first the legacy language, then the features added through time)
The standards shell tools manpages (compilers, interprets, ocamlbuild etc.)
The standard libraries
I noted from your previous questions that you use non-standard tools, such as opam and several libraries, make sure to check their documentations and note that some can extend your syntax.
I have to admit that the doc generally assumes people reading it already know about the concepts presented but you don't need to use them at first to master the language.
Happy hacking !
It is a polymorhic variant, that do bot need to be defined before usage. It is something between lisp's symbols and common ADT's. You think of it as a syntactically lighter version version of common ADTs.
I would suggest you to use utop as a playing ground to learn OCaml. Indeed, it is a damn easy language, it looks like to me that you have atacked it from a wrong side, or working with a program that is obfuscated.
Related
I need a good, stable and, maybe, easy to use C++ parser library with C/C++ interface (C is preferred).
I hear that cint is good c++ interpreter. Can I use it (or some part of it) for this purpose?
Any suggestions?
See: http://clang.llvm.org/
It has both a C++ and a C interface (libclang).
C++ parsing is famously hard. AFAIK there are only three parsers that are acceptable by todays standards: EDG (widely used as a frontend in popular C++ compilers), GCC's and Microsoft's. And apparently, Microsoft has started using EDG's parser in VS2010, for Intellisense.
When you're looking at the free options, you're pretty much stuck at GCC. It can produce XML, though, so the easy part is there. (Easy by C++ parsing standards, that is)
Clang is the most up-to-date and mature option, with a decent C++ API (but no plain C). Elsa is a bit out of date and unmaintained, but still a usable choice. Both could be used as libraries as well as standalone XML frontends.
If you want to parse C or C++ code, there are some options:
http://bellard.org/tcc/
http://students.ceid.upatras.gr/~sxanth/ncc/
If you want to create a parser using C/C++, you can try:
http://boost-spirit.com/home/
http://dinosaur.compilertools.net/ Lex and Yacc
http://www.codeguru.com/csharp/.net/net_general/patterns/article.php/c12805 Flex and Bison
Our C++ Front End is able to parse a variety of C++ dialects (ANSI, GCC, MSVS), automatically builds ASTs whose nodes are marked with precise source positions and are decorated with any nearby comment text, and builds a full symbol table. (EDIT Jan 2013: the C++ front end has been able to handle C++11 for quite awhile now).
The C++ front end is built on top of our DMS Software Reengineering Toolkit, generalized compiler technology for program analysis and transformation, designed to support custom tool building. The C++ front end includes a preprocessor, in which the preprocessor directives can be expanded or not collectively or individually as appropriate for the task. It also includes full symbol construction with all the nasty Koenig lookup stuff.
DMS accepts explicit language definitions (that's how it understands C++; there are also fron ends for C, C#, Java, COBOL, and variety of other languages). DMS provides general parsing, symbol table building, flow analysis machinery, procedural APIs for tree navigation/inspection/modification, source-to-source transformation, and AST-to-source text regeneration including the original comments, number radices, etc. All of these capabilities are available for use by the C++ Front End.
DMS is also designed to handle the scale required for serious tasks. Often you need not just one compilation unit (which is what GCC will give you at best) but access to an entire set. DMS has been used to analyze/transform thousands of C++ compilation units, and literally tens of thousands of C compilation units (on a 25 million line application).
"Easy to use library" is an oxymoron when it comes to program manipulation tools. The langauges themselves are complex (C++ being one of the most difficult and getting worse with C++0X) and that induces complexity in the nature of the questions you can ask and what the answers look like (e.g. "are there any template instantions that can modify local variable X in method Y in class C in any namespace N?"). The questions themselves are hard.
What you want is a library with the necessary complexity to let you carry off your task. DMS has been under continuous development for the last 15 years, to provide that necessary complexity. If you want to do serious program processing, I claim you will need that information.
As proof, DMS has been used to carry out massive automated reengineering of C++-based mission avionics software for Boeing. I don't believe there are any other tools that can do this. (Clang looks to be trying, but only for C++. YMMV).
I don't know for cint, but I heard people use gcc-xml for this.
I have been looking for a good stand-alone library too, but haven't found any.
If you're feeling brave the links in the answer to "is there a yacc-able C++ grammar?" might be helpful. Gcc-xml and clang have already been suggested and Swig also has an XML output which depending on what you're trying to achieve might be relevant.
I did not try it, but I think that best choice will be getting modules for parsing from some popular open source compiler like gcc for C++;
Maybe you'll find something interesting here http://www.nobugs.org/developer/parsingcpp/
The problems parsing C++ are well known. It can't be parsed purely based on syntax, it can't be done as LALR (whatever the term is, i'm not a language theorist), the language spec is a zillion pages, etc. For that and other reasons I'm deciding on an alternative language for my personal projects.
Vala looks like a good language. Although providing many improvements over C++, is just as troublesome to parse? Or does it have a neat, reasonable length formal grammar, or some logical description, suitable for building parsers for compilers, source analyzers and other tools?
Whatever the answer, does that go for the Genie alternative syntax?
(I also wonder albeit less intensely about D and other post-C++ non-VM languages.)
C++ is one of the most complex (if not the most complex) programming language to parse in common use. Of particular difficulty is it's name lookup rules and template instantiation rules. C++ is not parsable using a LALR(1) parser (such as the parsers generated by Bison and Yacc), but it is by all means parsable (after all, people use parsers which have no problem parsing C++ every day). (In fact, early versions of G++ were built on top of Bison's Generalized LR parser framework Actually not, see comments) before it was more recently replaced with a hand written recursive descent parser)
On the other hand, I'm not sure I see what "improvements" Vala offers over C++. The languages look to attempt to accomplish the same goals. On the other hand, you're probably not going to find much outside of GTK+ written with Vala interfaces. You're going to be using C interfaces to everything else, which really defeats the point of using such a language.
If you don't like C++ due to it's complexity, it might be a good idea to consider Objective-C instead, because it is a simple extension of C, (like Vala), but has a much larger community of programmers for you to draw upon given it's foundation for everything in Mac land.
Finally, I don't see why the difficulty of parsing the language itself has to do with what a programmer should be caring about in order to use the language. Just my 2 cents.
It's pretty simple. You can use libvala to do both parsing, semantic analyzing and code generation instead of writing your own.
We are going to start a new project in our team which consists of less than 10 developers.
We have access to modern IDEs such as VS2010.
The project is extremely dynamic (users' needs change very quick) and cross platform. Therefore, I need a highly readable and very detailed C++ coding standard so new developers can easily change the old codes in future. I also need a not to write list so the code will compile on different OSes (at least windows and linux).
Is there such a standard?
Are coding standards expired already?
Coding standards remain an issue because everyone secretly thinks they can solve all the world's programming problems with a very clever coding standard. And then forcing programmers to follow them. (Pretty much like programming programmers.)
Unfortunately, few coding standards address the issues that matter in a complex project like:
how to cleanly and effectively partition and model a problem
how program partitions should best interact with others
how an explanation of logic ("comment") should be written to explain the code
Instead, most coding standards address trivia like:
indentation and brace style
whether comments should be present or not
mechanical rules about constructing identifiers
placing arbitrary limits on characters in a line, number of parameters, etc., etc.
As for the primary question, I don't know of any good detailed standards other than design and implement code which other engineers would be proud of.
Read C++ Coding Standards. It is not what most people would call a coding standards document, but you probably want to read it. One of the first guides is do not swell the small stuff (do not put too much emphasis on details: focus on rules that affect the semantic not the syntax, as in prefer RAII over raw pointers instead of add braces everywhere, in it's own line and indenting 3 spaces)
As far as coding standard go, in most cases, it's less important what the specific coding standards are, so long as they're firmly in place. Tabs vs. space? Who cares. Pick one and go with it. Curly braces on the same line as the conditional or the next line? Who cares. Pick one and stay consistent.
I personally like the Linux kernel coding standards.
http://www.kernel.org/doc/Documentation/CodingStyle
It is for C, and not C++, but it may be a good place to start on the standards for your project. Unfortunately, I doubt it offers suggestions on a "do not write" list.
I highly recommend the Google style guide, which I haven't stopped using since interning there two years ago. The link above enumerates the rules in detail, along with each rule's justification in terms of pros and cons.
It is indeed highly readable and very detailed, but the important rules (the ones that come up all the time) are few and easy to remember. They have really streamlined my C++ coding by giving consistency to my naming and function argument-passing conventions.
I know you're using an IDE, but emacs users can use their "google.el" file for automatic formatting. There's also a powerful "cpplint" script that runs through a source file, printing out style violations in the same warning format as used by gcc. This lets you quickly fix style violations before checking in a file. If your IDE can parse gcc warnings and jump from warning to warning in a source file, then fixing such violations becomes a snap. Emacs and Eclipse CDT do this, as do other editors/IDEs.
I would like to create a domain specific language as an augmented-C++ language. I will need mostly two types of contructs:
Top-level constructs for specialized types or declarations
In-code constructs, i.e. to add primitives to make functions calls or idiom easier
The language will be used for scientific computing purposes, and will ultimately be translated into plain C++. C++ has been chosen as it seems to offer a good compromise between: ease of use, efficiency and availability of a wide range of libraries.
A previous attempt using flex and bison failed due to the complexity of the C++ syntax. The existing parser can still fail on some constructs. So we want to start over, but on better bases.
Do you know about similar projects? And if you attempted to do so, what tools would you use? What would be the main pitfalls? Would you have recommendations in term of syntax?
There are many (clever) attempts to have domain specific languages within the C++ language.
It's usually called DSEL for Domain Specific Embedded Language. For example, you could look up the Boost.Spirit syntax, or Boost.rdb (in the boost vault).
Those are fully compliant C++ libraries which make use of C++ syntax.
If you want to hide some complexity, you might add in a few macros.
I would be happy to provide some examples if you gave us something to work with :)
You can try extending an open source Elsa C++ parser (it is now a part of a Mozilla's Pork project):
https://wiki.mozilla.org/Pork
The way to extend C++ is not to try to extend the language, which will be extremely difficult and probably break as new base compiler releases implement new features, but to write class libraries to support your problem domain. This has been what C++ programming has been all about since the language's inception.
If you really want to extend C++, you'll need a full C++ parser plus name and type resolution. As you've found out, this is pretty hard. Your best solution is to get an existing one and modify it.
Our DMS Software Reengineering Toolkit is an infrastructure for implementing langauge processors. It is
designed to support the construction of tools that parse languages, carry out transformations, and spit out the same language (with enhanced code) or a different language/dialect.
DMS has a full C++ Front End, that parses C++, builds abstract syntax trees and symbol tables (e.g., all that name and type resolution stuff).
The DMS/C++ front end is provided with DMS in source form, so that it can be customized to achieve the kind of effect you want. You'd define your DSL as an extension of the C++ front end, and then write transformations that convert your special constructs into "vanilla" C++ constructs, and then spit out compilable result.
DMS/C++ have been used for a wide variety of transformation tasks, including ones that involved extending C++ as you've described, and including tasks that carry out massive reorganizations of large C++ applications. (See the Publications at that website).
To solve you first bullet, maybe you can use C++0x new features "initializer lists", and "user defined litterals" avoiding the need for a new parser. They may help for the second bullet, too.
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What are some good tools for getting a quick start for parsing and analyzing C/C++ code?
In particular, I'm looking for open source tools that handle the C/C++ preprocessor and language. Preferably, these tools would use lex/yacc (or flex/bison) for the grammar, and not be too complicated. They should handle the latest ANSI C/C++ definitions.
Here's what I've found so far, but haven't looked at them in detail (thoughts?):
CScope - Old-school C analyzer. Doesn't seem to do a full parse, though. Described as a glorified 'grep' for finding C functions.
GCC - Everybody's favorite open source compiler. Very complicated, but seems to do it all. There's a related project for creating GCC extensions called GEM, but hasn't been updated since GCC 4.1 (2006).
PUMA - The PUre MAnipulator. (from the page: "The intention of this project is to
provide a library of classes for the analysis and manipulation of C/C++ sources. For this
purpose PUMA provides classes for scanning, parsing and of course manipulating C/C++
sources."). This looks promising, but hasn't been updated since 2001. Apparently PUMA has been incorporated into AspectC++, but even this project hasn't been updated since 2006.
Various C/C++ raw grammars. You can get c-c++-grammars-1.2.tar.gz, but this has been unmaintained since 1997. A little Google searching pulls up other basic lex/yacc grammars that could serve as a starting place.
Any others?
I'm hoping to use this as a starting point for translating C/C++ source into a new toy language.
Thanks!
-Matt
(Added 2/9): Just a clarification: I want to extract semantic information from the preprocessor in addition to the C/C++ code itself. I don't want "#define foo 42" to disappear into the integer "42", but remain attached to the name "foo". This, unfortunately, excludes several solutions that run the preprocessor first and only deliver the C/C++ parse tree)
Parsing C++ is extremely hard because the grammar is undecidable. To quote Yossi Kreinin:
Outstandingly complicated grammar
"Outstandingly" should be interpreted literally, because all popular languages have context-free (or "nearly" context-free) grammars, while C++ has undecidable grammar. If you like compilers and parsers, you probably know what this means. If you're not into this kind of thing, there's a simple example showing the problem with parsing C++: is AA BB(CC); an object definition or a function declaration? It turns out that the answer depends heavily on the code before the statement - the "context". This shows (on an intuitive level) that the C++ grammar is quite context-sensitive.
You can look at clang that uses llvm for parsing.
Support C++ fully now link
The ANTLR parser generator has a grammar for C/C++ as well as the preprocessor. I've never used it so I can't say how complete its parsing of C++ is going to be. ANTLR itself has been a useful tool for me on a couple of occasions for parsing much simpler languages.
Depending on your problem GCCXML might be your answer.
Basically it parses the source using GCC and then gives you easily digestible XML of parse tree.
With GCCXML you are done once and for all.
pycparser is a complete parser for C (C99) written in Python. It has a fully configurable AST backend, so it's being used as a basis for any kind of language processing you might need.
Doesn't support C++, though. Granted, it's much harder than C.
Update (2012): at this time the answer, without any doubt, would be Clang - it's modular, supports the full C++ (with many C++-11 features) and has a relatively friendly code base. It also has a C API for bindings to high-level languages (i.e. for Python).
Have a look at how doxygen works, full source code is available and it's flex-based.
A misleading candidate is GOLD which is a free Windows-based parser toolkit explicitly for creating translators. Their list of supported languages refers to the languages in which one can implement parsers, not the list of supported parse grammars.
They only have grammars for C and C#, no C++.
Parsing C++ is a very complex challenge.
There's the Boost/Spirit framework, and a couple of years ago they did play with the idea of implementing a C++ parser, but it's far from complete.
Fully and properly parsing ISO C++ is far from trivial, and there were in fact many related efforts. But it is an inherently complex job that isn't easily accomplished, without rewriting a full compiler frontend understanding all of C++ and the preprocessor. A pre-processor implementation called "wave" is available from the Spirit folks.
That said, you might want to have a look at pork/oink (elsa-based), which is a C++ parser toolkit specifically meant to be used for source code transformation purposes, it is being used by the Mozilla project to do large-scale static source code analysis and automated code rewriting, the most interesting part is that it not only supports most of C++, but also the preprocessor itself!
On the other hand there's indeed one single proprietary solution available: the EDG frontend, which can be used for pretty much all C++ related efforts.
Personally, I would check out the elsa-based pork/oink suite which is used at Mozilla, apart from that, the FSF has now approved work on gcc plugins using the runtime library license, thus I'd assume that things are going to change rapidly, once people can easily leverage the gcc-based C++ parser for such purposes using binary plugins.
So, in a nutshell: if you the bucks: EDG, if you need something free/open source now: else/oink are fairly promising, if you have some time, you might want to use gcc for your project.
Another option just for C code is cscout.
The grammar for C++ is sort of notoriously hairy. There's a good thread at Lambda about it, but the gist is that C++ grammar can require arbitrarily much lookahead.
For the kind of thing I imagine you might be doing, I'd think about hacking either Gnu CC, or Splint. Gnu CC in particular does separate out the language generation part pretty thoroughly, so you might be best off building a new g++ backend.
Actually, PUMA and AspectC++ are still both actively maintained and updated. I was looking into using AspectC++ and was wondering about the lack of updates myself. I e-mailed the author who said that both AspectC++ and PUMA are still being developed. You can get to source code through SVN https://svn.aspectc.org/repos/ or you can get regular binary builds at http://akut.aspectc.org. As with a lot of excellent c++ projects these days, the author doesn't have time to keep up with web page maintenance. Makes sense if you've got a full time job and a life.
how about something easier to comprehend like tiny-C or Small C
Elsa beats everything else I know hands down for C++ parsing, even though it is not 100% compliant. I'm a fan. There's a module that prints out C++, so that may be a good starting point for your toy project.
See our C++ Front End
for a full-featured C++ parser: builds ASTs, symbol tables, does name
and type resolution. You can even parse and retain the preprocessor
directives. The C++ front end is built on top of our DMS Software Reengineering
Toolkit, which allows you to use that information to carry out arbitrary
source code changes using source-to-source transformations.
DMS is the ideal engine for implementing such a translator.
Having said that, I don't see much point in your imagined task; I don't
see much value in trying to replace C++, and you'll find building
a complete translator an enormous amount of work, especially if your
target is a "toy" language. And there is likely little point in
parsing C++ using a robust parser, if its only purpose is to produce
an isomorphic version of C++ that is easier to parse (wait, we postulated
a robust C++ already!).
EDIT May 2012: DMS's C++ front end now handles GCC3/GCC4/C++11,Microsoft VisualC 2005/2010. Robustly.
EDIT Feb 2015: Now handles C++14 in GCC and MS dialects.
EDIT August 2015: Now parses and captures both the code and the preprocessor directives in a unified tree.
EDIT May 2020: Has been doing C++17 for the past few years. C++20 in process.
A while back I attempted to write a tool that will automatically generate unit tests for c files.
For preprosessing I put the files thru GCC. The output is ugly but you can easily trace where in the original code from the preprocessed file. But for your needs you might need somthing else.
I used Metre as the base for a C parser. It is open source and uses lex and yacc. This made it easy to get up and running in a short time without fully understanding lex & yacc.
I also wrote a C app since the lex & yacc solution could not help me trace functionality across functions and parse the structure of the entire function in one pass. It became unmaintainable in a short time and was abandoned.
What about using a tool like GNU's CFlow, that can analyse the code and produce charts of call-graphs, here's what the opengroup(man page) has to say about cflow. The GNU version of cflow comes with source, and open source also ...
Hope this helps,
Best regards,
Tom.