OCaml: Automate custom pretty-printer installing - ocaml

I have implemented a pretty-printer for a module. Currently I start up utop, load the dependencies then do #install_printer pp_custom;; where pp_custom is the pretty-printer.
I would like to automate this so that I can have it in a way that is similar to the lacaml library where the pretty-printer for the matrix is "installed" by default.
How would I go about to doing that?

In short, you need to run #install_printer directive whenever you load your library in the top. I'm using the following code to evaluate code in the toplevel:
open Core_kernel.Std
open Or_error
let eval_exn str =
let lexbuf = Lexing.from_string str in
let phrase = !Toploop.parse_toplevel_phrase lexbuf in
Toploop.execute_phrase false Format.err_formatter phrase
let eval str = try_with (fun () -> eval_exn str)
It depends on Core_kernel, but you can get rid of this easily, by just using eval_exn instead of eval (the last one wraps a possible exception into the Or_error monad). Once you've got the eval function, it can be used to load your printers:
let () = eval (sprintf "#install_printer %s;;" printer)
where printer is the name of the pretty printing function (usually qualified with a module name). Usually, one put such code into the separate library, named library.top, where library is the name of your library.
For further automation, you can require all types, that you want to be auto-printable in toplevel, to register itself in a central registry, and then call all registered printers, instead of enumerating them by hand. To see all this working at once, you can take a look at the BAP library. It has a sublibrary called bap.top that automatically installs all printers. Each type that is desired to be printable implements Printable signature, using Printable.Make functor, that not only derives many printing functions from the basic definition, but also registers the generated pretty-printers in Core_kernel's Pretty_printer registry (you can use your own registry, this is just a set of strings, nothing more). When bap.top library is loaded into the toplevel (using require or load directive), it enumerates all registered printers and install them.

Related

Any good usage examples of an AST transformation with ppx_driver (register_transformation_using_ocaml_current_ast)?

tl;dr I'm trying to make a source transformation binary using AST_mapper and ppx_driver. I can't figure out how to get the example in the AST_mapper docs to be used by ppx_driver. Are there any good examples of how to use Ppx_driver.register_transformation_using_ocaml_current_ast?
I'm trying to port the example AST_mapper in the docs to be compatible with ppx_driver. Specifically, I'm looking to create a binary that takes source as input, transforms the source using this test mapper, and then outputs the transformed source. Unfortunately, the default main provided by Ast_mapper only accepts Ocaml AST as input (and presumably produces it as output). This is undesirable, because I don't want to have to run this through ocamlc with -dsource to get my output.
Here's my best stab at porting this:
test_mapper.ml
open Asttypes
open Parsetree
open Ast_mapper
let test_mapper argv =
{ default_mapper with
expr = fun mapper expr ->
Pprintast.expression Format.std_formatter expr;
match expr with
| { pexp_desc = Pexp_extension ({ txt = "test" }, PStr [])} ->
Ast_helper.Exp.constant (Ast_helper.Const.int 42)
| other -> default_mapper.expr mapper other; }
let test_transformation ast =
let mapper = (test_mapper ast) in
mapper.structure mapper ast
let () =
Ppx_driver.register_transformation_using_ocaml_current_ast
~impl:test_transformation
"test_transformation"
A few things to note:
The example from the docs didn't work out of the box (before introducing ppx_driver): Const_int 42 had to be replaced with Ast_helper.Const.int 42
For some reason test_mapper is Parsetree.structure -> mapper. (It is unclear to me why a recursive transformation needs the structure to create the mapper, but no matter.) But, this type isn't what Ppx_driver.register_transformation_using_ocaml_current_ast expects. So I wrote a sloppy wrapper test_transformation to make the typechecker happy (that is loosely based off how Ast_mapper.apply_lazy appears to apply a mapper to an AST so in theory it should work)
Unfortunately, after compiling this into a binary:
ocamlfind ocamlc -predicates ppx_driver -o test_mapper test_mapper.ml -linkpkg -package ppx_driver.runner
And running it on a sample file:
sample.ml
let x _ = [%test]
with the following:
./test_mapper sample.ml
I don't see any transformation occur (the sample file is regurgitated verbatim). What's more, the logging Pprintast.expression that I left in the code doesn't print anything, which suggests to me that my mapper never visits anything.
All of the examples I've been able to find in the wild are open sourced by Jane Street (who wrote ppx_*) and seem to either not register their transformation (perhaps there's some magic detection going on that's going over my head) or if they do they use Ppx_driver.register_transformation ~rules which uses Ppx_core.ContextFree (which doesn't seem to be complete and won't work for my real use case--but for the purposes of this question, I'm trying to keep things generally applicable).
Are there any good examples of how to do this properly? Why doesn't ppx_driver use my transformation?
If you want to make a standalone rewriter with a single module, you need to add
let () = Ppx_driver.standalone ()
to run the rewriter and links with ppx_driver and not ppx_driver.runner: ppx_driver.runner runs the driver as soon as it is loaded, therefore before your transformation is registered. Note also that you should at least specify a specific Ast version and uses Ppx_driver.register_transformation rather than Ppx_driver.register_transformation_using_current_ocaml_ast otherwise there is little point in using ppx_driver rather than doing the parsing by hand with compiler-libs and the Pparse module.

Using Metaclasses for self-registering plugins? (Approach help)

I'm trying to write a Python (2.7) library which loads certain classes at runtime. These classes contain a predefined set of methods.
My approach is to define a few Metaclasses which I work with in my library. I would for example define a "Navigation" Metaclass and work with it in the library. Then someone could write a class "Mainmenu" which contains some type of type definition that it is a "Navigation" plugin. And then the Library could use this class.
I am able to load modules and I'm able to write Metaclasses. My problem lies in combining these two things.
First there is the problem that I want the "plugin-classes" to be in a different (configurable) folder. So I can not do:
__metaclass__ = Navigation
because the Navigation class is part of my library and won't be there in the plugin-folder...
How could I solve the Problem of telling the type that the plugin is for? (Navigation, content.... e.g)
EDIT2: I solved the following problem. I found out that I can just ask the module to give me a dict.
My first problem still exists though
EDIT:
I managed registering and loading "normal" classes with a registry up until the following point:
from os import listdir
from os.path import isfile, join
import imp
class State:
registry = {}
def register_class(self,target_class):
self.registry[target_class.__name__] = target_class
print target_class.__name__+" registered!"
def create(self,classname):
tcls = self.registry[classname]
print self.registry[classname]
return tcls()
s = State()
mypath = """C:\metatest\plugins"""
files = [f for f in listdir(mypath) if isfile(join(mypath, f))]
for f in files:
spl = f.split(".")
if spl[1] == "py":
a = imp.load_source(spl[0], mypath + """\\""" + f)
s.register_class(a)
The problem I have at the end now is, that "a" is the loaded module, so it is a module-object. In my case there is only one class in it.
How can I get a Class object from the loaded module, so I can register the class properly??
So - let's check your problem steping back on your current proposal.
You need a way to have plug-ins for a larger system - the larger system won't know about the plug-ins at coding time - but the converse is not true: your plugins should be able to load modules, import base classes and call functions on your larger system.
Unless you really have something so plugable that plug-ins can work with more than one larger system. I doubt so, but if that is the case you need a framework that can register interfaces and retrieve classes and adapter-implementations between different classes. That framework is Zope Interface - you should read the documentation on it here: https://zopeinterface.readthedocs.io/en/latest/
Much more down to earth will be a plug-in system that sacans some preset directories for Python files and import those. As I said above, there is no problem if these files do import base classes (or metaclasses, for the record) on your main system: these are already imported by Python in the running process anyway, their import in the plug-in will just make then show up as available on the plug-in code.
You can use the exact code above, just add a short metaclass to register derived classes from State - you can maketeh convention that each base class for a different plug-in category have the registry attribute:
class RegistryMeta(type):
def __init__(cls, name, bases, namespace):
for base in cls.__mro__:
if 'registry' in base.__dict__:
if cls.__name__ in base.registry:
raise ValueError("Attempting to registrate plug-in with the name {} which is already taken".format(cls.__name__))
base.registry[cls.__name__] = cls
break
super(RegistryMeta, cls).__init__(name, base, namespace)
class State(object):
__metaclass__ = RegistryMeta
registry = {}
...
(keep the code for scanning the directory and loading modules - just switch all directory separation bars to "/" - you still are not doing it right and is subject to surprises by using "\")
and on the plug-in code include:
from mysystem import State
class YourClassCode(State):
...
And finally, as I said in the comment : you should really check the possibility of using Python 3.6 for that. Among other niceties, you could use the __init_subclass__ special method instead of needing a custom metaclass for keeping your registries.

Org-mode library of babel: can't #'CALL what I define

I want to use the library of babel of org-mode to define a new Clojure function that would be accessible to any org-mode document.
What I did is to define that new function in a named codeblock like this:
#+NAME: foo
#+BEGIN_SRC clojure
(defn foofn
[]
(println "foo test"))
#+END_SRC
Then I saved that into my library of bable using C-c C-v i, then I selected the org file to save in the library and everything looked fine.
Then in another org file I wanted to call that block such that it becomes defined in that other context. So I used the following syntax:
#+CALL: foo
However when I execute that org file I am getting the following error:
Reference `nil' not found in this buffer
Which tell me that it can't find that named block.
Any idea what I am doing wrong? Also once it works, is there a way to add new parameters to that code block when called using #+CALL:?
Finally, where is supposed to be located my library of babel? (how to know if it got properly added or not?)
I am obviously missing some core information that I can't find in the worg documentation.
Try:
#+CALL: foo()
Also, check the value of the variable org-babel-library-of-babel to make sure that the C-c C-v i worked properly.

Joomla: Plugins for a plugin - how to 'advertise' capabilities?

I am working on a plugin which will have its own plugins to handle various events.
Now I'm thinking of enabling this plugins to add their own "commands". But I wonder how to treat that most efficiently. I have a list of my own commands which I search in the article anyway. Should I then just trigger a DoWhatYouWant($article)-event - or, since I do the searching (and parsing of params) anyway, perhaps I could build a global command-list and then trigger an "ExecuteCommand($article,$cmd,$params)"-event? Sounds nicer, but then (I think) I'd have to build this command-list (so that my program know what to look for), so every plugin would have to somehow 'advertise' what it could do, i.e. the names of commands it could handle - and I have no idea how that could be done.
Or is there a better (more standardized?) approach?
If you import your plugins trough the plugin helper
JPluginHelper::importPlugin('mycmdplugins');
then you can get all available commands which are supported by your sub plugins like
$cmds = JDispatcher::getInstance()->trigger('onMyAwesomeCmds');
With the $cmds variable you know now which commands are supported by the sub plugins and you can parse the article for them. Then you can do
foreach ($cmds as $cmd) {
preg_match_all("{".$cmd."*}", $article->text, $matches, PREG_SET_ORDER);
if (!empty($matches)) {
JDispatcher::getInstance()->trigger('onMyAwesome'.ucfirst($cmd), array($article, $params));
}
}
To eliminate more repeating tasks I suggest that the additional plugins will extend a base class from your plugins folder.

embedded Lua loading modules programmatically (C++)

I am embedding Lua in a C++ application.
I have some modules (for now, simple .lua scripts) that I want to load programmatically, as the engine is being started, so that when the engine starts, the module(s) is/are available to scripts without them having to include a require 'xxx' at the top of the script.
In order to do this, I need to be able to programmatically (i.e. C++ end), ask the engine to load the modules, as part of the initialisation (or shortly thereafter).
Anyone knows how I can do this?
Hmm, I just use the simple approach: My C++ code just calls Lua's require function to pre-load the Lua scripts I want preloaded!
// funky = require ("funky")
//
lua_getfield (L, LUA_GLOBALSINDEX, "require"); // function
lua_pushstring (L, "funky"); // arg 0: module name
err = lua_pcall (L, 1, 1, 0);
// store funky module table in global var
lua_setfield (L, LUA_GLOBALSINDEX, "funky");
// ... later maybe handle a non-zero value of "err"
// (I actually use a helper function instead of lua_pcall
// that throws a C++ exception in the case of an error)
If you've got multiple modules to load, of course, put it in a loop... :)
The easiest way is to add and edit a copy of linit.c to your project.