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I am porting an OCaml project to ReasonML, but first to BuckleScript. I seeded the project directory with
bsb init .
and copied over the *.ml files. Compiling with
npm run build
gives me error:
[1/6] Building src/demo.cmj
File "/d/ProgLang/reason/src/demo.ml", line 2, characters 7-17: Error: Unbound value Str.regexp
[2/6] Building src/lex.cmj
File "/d/ProgLang/reason/src/lex.ml", line 13, characters 26-44: Error: Unbound value Str.search_forward
My package.json has
"devDependencies": {
"bsb-native": "^4.0.7000"
}
and
./node_modules/bsb-native/vendor/ocaml/lib/ocaml contains files str.a str.cma str.cmi str.cmx str.cmxs str.mli, but no source like str.ml . Also, https://reasonml.github.io/api/Str.html documents the functions I need, but how can I link them in when targeting Javascript (node)?
I can live with both Javascript or native targets, but I want to upgrade from OCaml syntax to ReasonML. In case you need my demo.ml, here it is:
let qq=Str.regexp "/q/" and
() = Js.log "Hello, STR! BuckleScript"
The functionality exposed by the Str module is actually implemented in C, and is therefore not easily portable to JavaScript. Any JavaScript implementation of Regular Expressions would likely be significantly slower than the built-in JavaScript implementation as well.
Furthermore, providing a common interface to multiple implementations isn't trivial since Regular Expression implementations differ in more or less subtle ways and aren't fully compatible with each other. Most aren't even regular, despite the name.
There's been some discussion around how a common interface for JS and native regexes can be accomplished, but there's no obvious solution and I'm not aware that anything has been concluded. But I would think that at the very least you'd have to implement a parser that would only accept the common subset of regex syntax, before passing it on to the underlying regex engine to be parsed again, which would obviously have a notable performance impact and is non-trivial to implement.
For now, you should be able to use Js.Re for JavaScript regexes and conditional compilation in order to use Str or some other implementation natively.
Another alternative might be to compile ocaml-re to JavaScript using js-of-ocaml and then interface with that using externals. Or port the project to bsb if possible, to use it directly. That will likely increase the size of your code bundle significantly, however, and it's not particularly straightforward to accomplish.
I am currently writing a program that sits on top of a C++ interpreter. The user inputs C++ commands at runtime, which are then passed into the interpreter. For certain patterns, I want to replace the command given with a modified form, so that I can provide additional functionality.
I want to replace anything of the form
A->Draw(B1, B2)
with
MyFunc(A, B1, B2).
My first thought was regular expressions, but that would be rather error-prone, as any of A, B1, or B2 could be arbitrary C++ expressions. As these expressions could themselves contain quoted strings or parentheses, it would be quite difficult to match all cases with a regular expression. In addition, there may be multiple, nested forms of this expression
My next thought was to call clang as a subprocess, use "-dump-ast" to get the abstract syntax tree, modify that, then rebuild it into a command to be passed to the C++ interpreter. However, this would require keeping track of any environment changes, such as include files and forward declarations, in order to give clang enough information to parse the expression. As the interpreter does not expose this information, this seems infeasible as well.
The third thought was to use the C++ interpreter's own internal parsing to convert to an abstract syntax tree, then build from there. However, this interpreter does not expose the ast in any way that I was able to find.
Are there any suggestions as to how to proceed, either along one of the stated routes, or along a different route entirely?
What you want is a Program Transformation System.
These are tools that generally let you express changes to source code, written in source level patterns that essentially say:
if you see *this*, replace it by *that*
but operating on Abstract Syntax Trees so the matching and replacement process is
far more trustworthy than what you get with string hacking.
Such tools have to have parsers for the source language of interest.
The source language being C++ makes this fairly difficult.
Clang sort of qualifies; after all it can parse C++. OP objects
it cannot do so without all the environment context. To the extent
that OP is typing (well-formed) program fragments (statements, etc,.)
into the interpreter, Clang may [I don't have much experience with it
myself] have trouble getting focused on what the fragment is (statement? expression? declaration? ...). Finally, Clang isn't really a PTS; its tree modification procedures are not source-to-source transforms. That matters for convenience but might not stop OP from using it; surface syntax rewrite rule are convenient but you can always substitute procedural tree hacking with more effort. When there are more than a few rules, this starts to matter a lot.
GCC with Melt sort of qualifies in the same way that Clang does.
I'm under the impression that Melt makes GCC at best a bit less
intolerable for this kind of work. YMMV.
Our DMS Software Reengineering Toolkit with its full C++14 [EDIT July 2018: C++17] front end absolutely qualifies. DMS has been used to carry out massive transformations
on large scale C++ code bases.
DMS can parse arbitrary (well-formed) fragments of C++ without being told in advance what the syntax category is, and return an AST of the proper grammar nonterminal type, using its pattern-parsing machinery. [You may end up with multiple parses, e.g. ambiguities, that you'll have decide how to resolve, see Why can't C++ be parsed with a LR(1) parser? for more discussion] It can do this without resorting to "the environment" if you are willing to live without macro expansion while parsing, and insist the preprocessor directives (they get parsed too) are nicely structured with respect to the code fragment (#if foo{#endif not allowed) but that's unlikely a real problem for interactively entered code fragments.
DMS then offers a complete procedural AST library for manipulating the parsed trees (search, inspect, modify, build, replace) and can then regenerate surface source code from the modified tree, giving OP text
to feed to the interpreter.
Where it shines in this case is OP can likely write most of his modifications directly as source-to-source syntax rules. For his
example, he can provide DMS with a rewrite rule (untested but pretty close to right):
rule replace_Draw(A:primary,B1:expression,B2:expression):
primary->primary
"\A->Draw(\B1, \B2)" -- pattern
rewrites to
"MyFunc(\A, \B1, \B2)"; -- replacement
and DMS will take any parsed AST containing the left hand side "...Draw..." pattern and replace that subtree with the right hand side, after substituting the matches for A, B1 and B2. The quote marks are metaquotes and are used to distinguish C++ text from rule-syntax text; the backslash is a metaescape used inside metaquotes to name metavariables. For more details of what you can say in the rule syntax, see DMS Rewrite Rules.
If OP provides a set of such rules, DMS can be asked to apply the entire set.
So I think this would work just fine for OP. It is a rather heavyweight mechanism to "add" to the package he wants to provide to a 3rd party; DMS and its C++ front end are hardly "small" programs. But then modern machines have lots of resources so I think its a question of how badly does OP need to do this.
Try modify the headers to supress the method, then compiling you'll find the errors and will be able to replace all core.
As far as you have a C++ interpreter (as CERN's Root) I guess you must use the compiler to intercept all the Draw, an easy and clean way to do that is declare in the headers the Draw method as private, using some defines
class ItemWithDrawMehtod
{
....
public:
#ifdef CATCHTHEMETHOD
private:
#endif
void Draw(A,B);
#ifdef CATCHTHEMETHOD
public:
#endif
....
};
Then compile as:
gcc -DCATCHTHEMETHOD=1 yourfilein.cpp
In case, user want to input complex algorithms to the application, what I suggest is to integrate a scripting language to the app. So that the user can write code [function/algorithm in defined way] so the app can execute it in the interpreter and get the final results. Ex: Python, Perl, JS, etc.
Since you need C++ in the interpreter http://chaiscript.com/ would be a suggestion.
What happens when someone gets ahold of the Draw member function (auto draw = &A::Draw;) and then starts using draw? Presumably you'd want the same improved Draw-functionality to be called in this case too. Thus I think we can conclude that what you really want is to replace the Draw member function with a function of your own.
Since it seems you are not in a position to modify the class containing Draw directly, a solution could be to derive your own class from A and override Draw in there. Then your problem reduces to having your users use your new improved class.
You may again consider the problem of automatically translating uses of class A to your new derived class, but this still seems pretty difficult without the help of a full C++ implementation. Perhaps there is a way to hide the old definition of A and present your replacement under that name instead, via clever use of header files, but I cannot determine whether that's the case from what you've told us.
Another possibility might be to use some dynamic linker hackery using LD_PRELOAD to replace the function Draw that gets called at runtime.
There may be a way to accomplish this mostly with regular expressions.
Since anything that appears after Draw( is already formatted correctly as parameters, you don't need to fully parse them for the purpose you have outlined.
Fundamentally, the part that matters is the "SYMBOL->Draw("
SYMBOL could be any expression that resolves to an object that overloads -> or to a pointer of a type that implements Draw(...). If you reduce this to two cases, you can short-cut the parsing.
For the first case, a simple regular expression that searches for any valid C++ symbol, something similar to "[A-Za-z_][A-Za-z0-9_\.]", along with the literal expression "->Draw(". This will give you the portion that must be rewritten, since the code following this part is already formatted as valid C++ parameters.
The second case is for complex expressions that return an overloaded object or pointer. This requires a bit more effort, but a short parsing routine to walk backward through just a complex expression can be written surprisingly easily, since you don't have to support blocks (blocks in C++ cannot return objects, since lambda definitions do not call the lambda themselves, and actual nested code blocks {...} can't return anything directly inline that would apply here). Note that if the expression doesn't end in ) then it has to be a valid symbol in this context, so if you find a ) just match nested ) with ( and extract the symbol preceding the nested SYMBOL(...(...)...)->Draw() pattern. This may be possible with regular expressions, but should be fairly easy in normal code as well.
As soon as you have the symbol or expression, the replacement is trivial, going from
SYMBOL->Draw(...
to
YourFunction(SYMBOL, ...
without having to deal with the additional parameters to Draw().
As an added benefit, chained function calls are parsed for free with this model, since you can recursively iterate over the code such as
A->Draw(B...)->Draw(C...)
The first iteration identifies the first A->Draw( and rewrites the whole statement as
YourFunction(A, B...)->Draw(C...)
which then identifies the second ->Draw with an expression "YourFunction(A, ...)->" preceding it, and rewrites it as
YourFunction(YourFunction(A, B...), C...)
where B... and C... are well-formed C++ parameters, including nested calls.
Without knowing the C++ version that your interpreter supports, or the kind of code you will be rewriting, I really can't provide any sample code that is likely to be worthwhile.
One way is to load user code as a DLL, (something like plugins,)
this way, you don't need to compile your actual application, just the user code will be compiled, and you application will load it dynamically.
I have some logic in a C++ program that is not only insanely complex, it requires multiple solutions for which Prolog is ideal. It's sort of like a firewall config script, checking input for actions, but sometimes more that one action is required.
What I want is something like this:
class PrologEngine
{
LoadLogic(const char* filename) throw PrologException; // Load a file of prolog rules, predicates facts etc in textual format. Must be callable multiple times to load AND COMPILE (for speed) prolog rule files.
std::vector<std::string> Evaluate(const char* predicate_in_string_form = "execute(input, Result)") throw PrologException; Returns a vector of matching predicates in text form.
};
It needs no ability to call back into C++.
AMI Prolog seems to get it, but it's not available on Linux. I'm trying to use SWI-Prolog and can only find 2 examples and and incredibly byzantine API (my opinion)
Can anyone point me to an example that is close to what I'm looking for?
There is A C++ interface to SWI-Prolog, that's high level.
I'm fighting with it, here an example of bridging to OpenGL:
PREDICATE(glEvalCoord1d, 1) {
double u = A1;
glEvalCoord1d( u );
return TRUE;
}
This clean code hides many 'bizantinism', using implicit type conversion and some macro. The interface is well tought and bidirectional: to call Prolog from C++ there are PlCall ('run' a query, similar to Evaluate you expose in the answer) or a more structured PlQuery, for multiple results...
If you don't need to link to openGl, or can wait to ear about the answer that hopefully I'll get from SWI-Prolog mailing list, you should evaluate it.
If you don't mind rewriting the prolog code for use in a native c++ header only library, I'd look into the castor library:
http://www.mpprogramming.com/cpp/
I am working on a toy language that compiles to C++ based on lisp (very small subset of scheme), I am trying to figure out how to represent let expression,
(let ((var 10)
(test 12))
(+ 1 1)
var)
At first I thought execute all exprs then return the last one but returning will kill my ability to nest let expressions, what would be the way to go for representing let?
Also, any resources on source to source transformation is appriciated, I have googled but all I could fing is the 90 min scheme compiler.
One way to expand let is to treat it as a lambda:
((lambda (var test) (+ 1 1) var) 10 12)
Then, transform this to a function and a corresponding call in C++:
int lambda_1(int var, int test) {
1 + 1;
return var;
}
lambda_1(10, 12);
So in a larger context:
(display (let ((var 10)
(test 12))
(+ 1 1)
var))
becomes
display(lambda_1(10, 12));
There are a lot more details, such as needing to access lexical variables outside the let from within the let. Since C++ doesn't have lexically nested functions (unlike Pascal, for example), this will require additional implementation.
I'll try to explain a naive approach to compiling nested
lambdas. Since Greg's explanation of expanding let into a lambda
is very good, I won't address let at all, I'll assume that let is
a derived form or macro and is expanded into a lambda form that is
called immediately.
Compiling Lisp or Scheme functions directly into C or C++ functions
will be tricky due to the issues other posters raised. Depending on
the approach, the resulting C or C++ won't be recognizeable (or even
very readable).
I wrote a Lisp-to-C compiler after finishing Structure and Interpretation of Computer Programs (it's one of the final exercises, and actually I cheated and just wrote a translator from SICP byte code to C). The subset of C that it emitted didn't use C functions to handle Lisp functions at all. This is because the
register machine language in chapter 5 of SICP is really lower level
than C.
Assuming that you have some form of environments, which bind names to values, you can define the crux of function calling like this: extend the environment which the function was defined in with the formal parameters bound to the arguments, and then evaluate the body of the function in this new environment.
In SICP's compiler, the environment is held in a global variable, and there are other
global variables holding the argument list for a function call, as
well as the procedure object that is being called (the procedure object includes a pointer to the environment in which it was defined), and a label to jump to when a function returns.
Keep in mind that when you are compiling a lambda expression, there
are two syntactic components you know at compile-time: the formal
parameters and the body of the lambda.
When a function is compiled, the emitted code looks something like
this pseudocode:
some-label
*env* = definition env of *proc*
*env* = extend [formals] *argl* *env*
result of compiling [body]
...
jump *continue*
... where *env* and *argl* are the global variables holding the
environment and argument list, and extend is some function (this can
be a proper C++ function) that extends the environment *env* by
pairing up names in *argl* with values in [formals].
Then, when the compiled code is run, and there is a call to this
lambda somewhere else in your code, the calling convention is to put
the result of evaluating the argument list into the *argl* variable, put the return label in the *continue* variable, and then jump to some-label.
In the case of nested lambdas, the emitted code would look something
like this:
some-label
*env* = definition env of *proc*
*env* = extend [formals-outer] *argl* *env*
another-label
*env* = definition env of *proc*
*env* = extend [formals-inner] *argl* *env*
result of compiling [body-inner]
...
jump *continue*
rest of result of compiling [body-outer]
... somewhere in here there might be a jump to another-label
jump *continue*
This is a bit difficult to explain, and I'm sure I've done a muddled
job of it. I can't think of a decent example that doesn't involve me basically sloppily describing the whole chapter 5 of SICP. Since I spent the time to write this answer, I'm going to post it, but I'm very sorry if it's hopelessly confusing.
I strongly recommend SICP and Lisp in Small Pieces.
SICP covers metacircular interpretation for beginners, as well as a number of variants on the interpreter, and a byte code compiler which I have managed to obfuscate and mangle above. That's just the last two chapters, the first 3 chapters are just as good. It's a wonderful book. Absolutely read it if you haven't yet.
L.i.S.P includes a number of interpreters written in Scheme, a compiler to byte code and a compiler to C. I'm in the middle of it and can say with confidence it's a deep, rich book well worth the time of anyone interested in the implementation of Lisp. It may be a bit dated by this point, but for a beginner like me, it's still valuable. It's more advanced than SICP though, so beware. It incudes a chapter in the middle on denotational semantics which went basically right over my head.
Some other notes:
Darius Bacon's self-hosting Lisp to C compiler
lambda lifting, which is a more advanced technique that I think Marc Feeley uses
If you're looking for tools to help with source-to-source translation, I'd recommend ANTLR. It is most excellent.
However, you'll need to think about how to translate from a loosely-typed language (lisp) to a less-loosely-typed language (c). For example, in your question, what is the type of 10? A short? An int? A double?
It should turn this
int Yada (int yada)
{
return yada;
}
into this
int Yada (int yada)
{
SOME_HEIDEGGER_QUOTE;
return yada;
}
but for all (or at least a big bunch of) syntactically legal C/C++ - function and method constructs.
Maybe you've heard of some Perl library that will allow me to perform these kinds of operations in a view lines of code.
My goal is to add a tracer to an old, but big C++ project in order to be able to debug it without a debugger.
Try Aspect C++ (www.aspectc.org). You can define an Aspect that will pick up every method execution.
In fact, the quickstart has pretty much exactly what you are after defined as an example:
http://www.aspectc.org/fileadmin/documentation/ac-quickref.pdf
If you build using GCC and the -pg flag, GCC will automatically issue a call to the mcount() function at the start of every function. In this function you can then inspect the return address to figure out where you were called from. This approach is used by the linux kernel function tracer (CONFIG_FUNCTION_TRACER). Note that this function should be written in assembler, and be careful to preserve all registers!
Also, note that this should be passed only in the build phase, not link, or GCC will add in the profiling libraries that normally implement mcount.
I would suggest using the gcc flag "-finstrument-functions". Basically, it automatically calls a specific function ("__cyg_profile_func_enter") upon entry to each function, and another function is called ("__cyg_profile_func_exit") upon exit of the function. Each function is passed a pointer to the function being entered/exited, and the function which called that one.
You can turn instrumenting off on a per-function or per-file basis... see the docs for details.
The feature goes back at least as far as version 3.0.4 (from February 2002).
This is intended to support profiling, but it does not appear to have side effects like -pg does (which compiles code suitable for profiling).
This could work quite well for your problem (tracing execution of a large program), but, unfortunately, it isn't as general purpose as it would have been if you could specify a macro. On the plus side, you don't need to worry about remembering to add your new code into the beginning of all new functions that are written.
There is no such tool that I am aware of. In order to recognise the correct insertion point, the tool would have to include a complete C++ parser - regular expressions are not enough to accomplish this.
But as there are a number of FOSS C++ parsers out there, such a tool could certainly be written - a sort of intelligent sed for C++ code. The biggest problem would probably be designing the specification language for the insert/update/delete operation - regexes are obviously not the answer, though they should certainly be included in the language somehow.
People are always asking here for ideas for projects - how about this for one?
I use this regex,
"(?<=[\\s:~])(\\w+)\\s*\\([\\w\\s,<>\\[\\].=&':/*]*?\\)\\s*(const)?\\s*{"
to locate the functions and add extra lines of code.
With that regex I also get the function name (group 1) and the arguments (group 2).
Note: you must filter out names like, "while", "do", "for", "switch".
This can be easily done with a program transformation system.
The DMS Software Reengineering Toolkit is a general purpose program transformation system, and can be used with many languages (C#, COBOL, Java, EcmaScript, Fortran, ..) as well as specifically with C++.
DMS parses source code (using full langauge front end, in this case for C++),
builds Abstract Syntax Trees, and allows you to apply source-to-source patterns to transform your code from one C# program into another with whatever properties you wish. THe transformation rule to accomplish exactly the task you specified would be:
domain CSharp.
insert_trace():function->function
"\visibility \returntype \fnname(int \parametername)
{ \body } "
->
"\visibility \returntype \fnname(int \parametername)
{ Heidigger(\CppString\(\methodname\),
\CppString\(\parametername\),
\parametername);
\body } "
The quote marks (") are not C++ quote marks; rather, they are "domain quotes", and indicate that the content inside the quote marks is C++ syntax (because we said, "domain CSharp"). The \foo notations are meta syntax.
This rule matches the AST representing the function, and rewrites that AST into the traced form. The resulting AST is then prettyprinted back into source form, which you can compile. You probably need other rules to handle other combinations of arguments; in fact, you'd probably generalize the argument processing to produce (where practical) a string value for each scalar argument.
It should be clear you can do a lot more than just logging with this, and a lot more than just aspect-oriented programming, since you can express arbitrary transformations and not just before-after actions.