I am writing a transpiler from my desktop programming language to JavaScript.
I use gmp on the desktop, so am writing a thin wrapper to mimic the same entry points but use BigInt under the hood.
(NB Emscripten etc NOT involved) So far mpz and mpq are working pretty well, ~30 entry points each, done by hand, so now I'm wondering about mpfr.
Could mpfr be done as mpq with implied/capped denominator of 10^k (where k can be negative), and
accordingly truncated/BigInt numerator? I expect a bit of a struggle with mpfr_const_pi(), mpfr_sin/log/exp(), etc. I say 10^k but am not even certain of that vs 2^k.
I have studied https://github.com/MikeMcl/big.js and friends but no offence meant all that seems to pre-date BigInts, and I simply cannot find anything that implements floats via BigInt.
In short, what code needs to be in mpfr.js so that the following will work (ideally unaltered), obviously any partial ideas, hints, or tips are just as welcome as a full-blown working example. You can assume (eg) mpz_get_str() is available, or of course you can go with using (say) BigInt.toString() etc directly, and not overly panic about precisely where the decimal point has to go, or any "%.75Rf" related nuances. I just need something to get the ball rolling.
<script src="mpfr.js"></script>
<script>
mpfr_set_default_prec(252); // (enough for 75 decimal places)
let one_third = mpfr_init(1); // (ok, non-std syntax, anyway init to 1)
mpfr_div_si(one_third,one_third,3);
console.log(mpfr_sprintf("%.75Rf",one_third);
</script>
I finally found this https://jrsinclair.com/articles/2020/sick-of-the-jokes-write-your-own-arbitrary-precision-javascript-math-library/ and I've now got pretty much everything I needed working.
While it is exactly what I was looking for, I should point out that it is deeply flawed, for instance there is a frankly outrageous memoize() function liberally applied, which no doubt vastly improved some pointless benchmark but would totally cripple real-world use, and other gross ineffiencies such as exp10(n) returns BigInt(1${[...new Array(n)].map(() => 0).join("")}), instead of the much saner
10n**BigInt(n). Nevertheless it is quite spirited and undeniably well meant, with plenty of good ideas.
Should anyone wish to see the results of my efforts I have uploaded the latest version: https://github.com/petelomax/Phix/blob/master/pwa/builtins/mpfr.js
I'm using the paper_trail gem to auto-create a versions history of my Page model.
In pages#show, I display the versions like so:
The most important element is the diff which shows the difference between the previous and the currently displayed version of a field, e.g. content. It looks like a diff on GitHub, and it is marked up well using <ins> for insertions and <del> for deletions.
The sad thing is that at the time being, I generate this diff using https://code.google.com/p/google-diff-match-patch/, a JavaScript library that's run in the browser of the user. I've done it this way because I didn't manage to find a Ruby gem or similar that does the same in a similar elegant way.
Well, I found https://github.com/samg/diffy and https://github.com/pvande/differ, but the diff of both gems aren't close as elegant: differ needs to know manually whether to diff by line, word, or character (while the used JavaScript decides this automatically and uses a combination of these options which feels very intuitive to me), and diffy doesn't offer an option for this. I don't know exactly how the JavaScript works, but it states that "Myer's diff algorithm" is used internally:
This library implements Myer's diff algorithm which is generally considered to be the best general-purpose diff. A layer of pre-diff speedups and post-diff cleanups surround the diff algorithm, improving both performance and output quality.
You can try it here: https://neil.fraser.name/software/diff_match_patch/svn/trunk/demos/demo_diff.html
Maybe use the following two strings to see a typical example of two versions of a page:
This is the about page.
Put markdowwn formated content here.
and
This is the about page.
Put markdown formatted here content.
A [link to page 11](11). And another one: [](11).
It results in something like this:
The problem with this approach is that it's run in the browser, so I can't mutate the generated code in my Rails application anymore. So I wonder whether there's an easy way to get similar diff results using e.g. a command line tool like diff? Maybe even git could be of use?
I need to develop natural language querying tool for a structured database. I tried two approaches.
using Python nltk (Natural Language Toolkit for python) using
Javascript and JSON (for data source)
In the first case I did some NLP steps to format the natural query by doing removing stop words, stemming, finally mapping keywords using featured grammar mapping. This methodology works for simple scenarios.
Then I moved to second approach. Finding the data in JSON and getting corresponding column name and table name , then building a sql query. For this one, I also implemented removing stop words, stemming using javascript.
Both of these techniques have limitations.I want to implement semantic search approach.
Please can anyone suggest me better approach to do this..
Semantic parsing for NLIDB (natural language interface to data bases) is a very evolved domain with many techniques: rule based methods (involving grammars) or machine learning techniques. They cover a large range of query inputs, and offer much more results than pure NL processing or regex methods.
The technique I favor is based on Feature based context-free grammars FCFG. For starters, in the NTLK book available online, look for the string "sql0.fcfg". The code example shows how to map the NL phrase structure query "What cities are located in China" into an SQL query "SELECT City FROM city_table WHERE Country="china" via the feature "SEM" or semantics of the FCFG.
I recommend Covington's books
NLP for Prloog Programmers (1994)
Prolog Programming in Depth (1997)
They will help You go a long way. These PDF's are downloadable from his site.
As I commented, I think you should add some code, since not everyone has read the book.
Anyway my conclusion is that yes, as you said it has a lot of limitations and the only way to achieve more complex queries is to write very extensive and complete grammar productions, a pretty hard work.
I am trying to substitude or replace the JSON-JavaScript-Object in case it is not available - what would be a neat way to achieve this?
Situation:
I have some code which uses JSON.parse and other functions to handle JSONs, but I have to migrate this code to be compatible to the Maple-Browser of a Samsung 2011-Series, which does not have a built-in JSON-Object.
jquery-1.6.2 lib is available; adding another lib is possible.
Solution attempts:
Found this nice blog http://www.greenhughes.com/content/experimental-couchdb-powered-samsung-internettv-app, which pretty much sums this problem up and even proviedes some solution. But this attempt seems to be 2 years old and I am looking for an improved solution.
Goal:
I would like to keep as much of my code as possible as it is and only handle somewhere the sitation, when a build-in JSON-Object is not available and then make it available in a way, that I do not have to change the calls to this Object.
Many thanks to any input or ideas to achieve this goal!
During my routine work, i happened to write the chained javascript function which is something like LINQ expression to query the JSON result.
var Result = from(obj1).as("x").where("x.id=5").groupby("x.status").having(count("x.status") > 5).select("x.status");
It works perfectly and give the expected result.
I was wondering this looks awesome if the code is written like this (in a more readable way)
var Result = from obj1 as x where x.status
groupby x.status having count(x.status) > 5
select x.status;
is there a way to achieve this??
Cheers
Ramesh Vel
No. JavaScript doesn't support this.
But this looks quite good too:
var Result = from(obj1)
.as("x")
.where("x.id=5")
.groupby("x.status")
.having(count("x.status") > 5)
.select("x.status");
Most people insist on trying to metaprogram from inside their favorite language. That doesn't work if the language doesn't support metaprogramming well; other answers have observed that JavaScript does not.
A way around this is to do metaprogramming from outside the language, using
program transformation tools. Such tools can parse source code, and carry out arbitrary transformations on it (that's what metaprogramming does anyway) and then spit the revised program.
If you have a general purpose program transformation system, that can parse arbitrary languages, you can then do metaprogramming on/with whatever language you like. See our DMS Software Reengineering Toolkit for such a tool, that has robust front ends for C, C++, Java, C#, COBOL, PHP, and ECMAScript and a number of other programming langauges, and has been used for metaprogramming on all of these.
In your case, you want to extend the JavaScript grammar with new syntax for SQL queries, and then transform them to plain JavaScript. (This is a lot like Intentional Programming)
DMS will easily let you build a JavaScript dialect with additional rules, and then you can use its program transformation capabilities to produce the equivalent standard Javascript.
Having said, that, I'm not a great fan of "custom syntax for every programmer on the planet" which is where Intentional Programming leads IMHO.
This is a good thing to do if there is a large community of users that would find this valuable. This idea may or may not be one of them; part of the problem is you don't get to find out without doing the experiment, and it might fail to gain enough social traction to matter.
although not quite what you wanted, it is possible to write parsers in javascript, and just parse the query (stored as strings) and then execute it. e.g.,using libraries like http://jscc.jmksf.com/ (no doubt there are others out there) it shouldnt be too hard to implement.
but what you have in the question looks great already, i m not sure why you'd want it to look the way you suggested.
Considering that this question is asked some years ago, I will try to add more to it based on the current technologies.
As of ECMAScript 6, metaprogramming is now supported in a sense via Symbol, Reflect and Proxy objects.
By searching on the web, I found a series of very interesting articles on the subject, written by Keith Kirkel:
Metaprogramming in ES6: Symbols and why they're awesome
In short, Symbols are new primitives that can be added inside an object (without practically being properties) and are very handy for passing metaprogramming properties to it among others. Symbols are all about changing the behavior of existing classes by modifying them (Reflection within implementation).
Metaprogramming in ES6: Part 2 - Reflect
In short, Reflect is effectively a collection of all of those “internal methods” that were available exclusively through the JavaScript engine internals, now exposed in one single, handy object. Its usage is analogous to the Reflection capabilities of Java and C#. They are used to discover very low level information about your code (Reflection through introspection).
Metaprogramming in ES6: Part 3 - Proxies
In short, Proxies are handler objects, responsible for wrapping objects and intercepting their behaviors through traps (Reflection through intercession).
Of course, these objects provide specific metaprogramming capabilities, much more restrictive compared to metaprogramming languages, but still can provide handy ways of basic metaprogramming, mainly through Reflection practices, in fact.
In the end, it is worth mentioning that there is some worth-noticing ongoing research work on staged metaprogramming in JavaScript.
Well, in your code sample:
var Result = from(obj1)
.as("x")
.where("x.id=5")
.groupby("x.status")
.having(count("x.status") > 5)
.select("x.status");
The only problem I see (other than select used as an identifier) is that you embed a predicate as a function argument. You'd have to make it a function instead:
.having(function(x){ return x.status > 5; })
JavaScript has closures and dynamic typing, so you can do some really nifty and elegant things in it. Just letting you know.
In pure JS no you can not. But with right preprocessor it is possible.
You can do something similar with sweet.js macros or (God forgive me) GPP.
Wat you want is to change the javascript parser into an SQL parser. It wasn't created to do that, the javascript syntax doesn't allow you to.
What you have is 90% like SQL (it maps straight onto it), and a 100% valid javascript, which is a great achievement. My answer to the question in the title is: YES, metaprogramming is possible, but NO it won't give you an SQL parser, since it's bound to use javascript grammar.
Maybe you want something like JSONPath if you've got JSON data. I found this at http://www.json.org/. Lots of other tools linked to from there if it's not exactly what you need.
(this is being worked on as well: http://docs.dojocampus.org/dojox/json/query)