I want something like Python's readline but in OCaml. I'm writing an OCaml program that takes in input like a shell or REPL would, and I would like to add history that is prompted with the arrow keys. Is there any library or built-in that provides this functionality?
Following ivg's suggestion, opam search readline shows:
linenoise -- this looks to offer the specific functionality you're looking for with very little overhead
zed -- this looks more full featured, and more flexible, but will likely be a bit more involved to use
I made a library to abstract over the Linenoise library to provide readline functionality. It also provides features to wait until delimiters are entered before accepting input.
ocamline: https://github.com/chrisnevers/ocamline
Related
Can I change the core functionality of Python, for example, rewrite it to use say("Hello world") instead of print("Hello world")?
If this is possible, how can this be done?
I see a few possibilities as to how to accomplish this. I've arranged them in order of how much programming is needed/how obnoxious they are:
Renaming builtins
If, as in your example, you are simply more comfortable using say() or printf() than print(), then you can, as others have answered, just alias the builtin function to your own function with something like say=print.
Rewriting builtins
Let's pretend we don't trust the official implementation of print() and we want to implement our own. A lot of the internals in Python such as stdin are contained in the sys library. You could, if you wanted, implement your own. I asked a question a couple years ago here that discussed how to rename the _ variable to ans which might be illuminating to take a look at.
Sending your code through a preprocessor
Ok, so gcc doesn't require C code as input. If you use the right precompiler flags, then you could get away with evaluating #define macros in your source code before you send it to python. Technically a valid answer, but obnoxious as heck.
Writing modules in another language
Cython (python written in C) can have modules written for it in C. You could build a wrapper for printf in C (or assembly, if you'd rather) and use that library in your python code.
Recompiling Python
Unfortunately, doing the above is not possible with all tokens. What if, in a fit of fancy, we'd like to use whilst loops instead of while loops? The only way to accomplish this is actually altering the functioning of python itself. Now, this isn't for the faint of heart or the new programmer. Compilers are really complicated.
Since, however, Python is open source and you can download the source code here, in theory, you could go into the compiler and manually make all the edits you want, then compile your version of python and use that. By no means would your code be portable (as essentially you'd be making a fork of python) but you could technically do it.
Or just conform to the Python standards. That works too.
Writing a PEP
Python is a living language. It's constantly being updated. The ruling body of "What gets included" is the BDFL-delegate and the Council, but anyone can write a Python Enhancement Proposal that proposes to change the language in some way. Most features in Python started out as a PEP. See PEP 0001 for more details.
yes you can just write
say = print
say("hello")
What is the easiest way to get some values (yes/no, numbers) into a Haskell program. The values should be bound to some variables and other questions should be asked based on previous inputs.
I am trying to solve a little problem for which I think Haskell is best suited. Especially for extending the functionality afterwards. An addition I am also trying to learn this language (I am new to Haskell but have some experience with Prolog, so have some idea about functional programming).
I was checking all he stuff relatd to GUI development, but this is actually an overkill to what I need. The input should be in response to some questions which are dependent on the state of the execution.
I hope this is clear enough.
EDIT:
I would like to have some "po-ups" like these. Not all at once, but just as a pop-up when needed.
It feels a little bit like your assumption is that Haskell is like Javascript here.
That is, it's very simple in Javascript to get a "popup" to display in a browser such as Chrome by using prompt("Are you hungry or thirsty?"), but that's only because the prompt function is built on top of the window object which the browser provides to allow developers to hook into the windowing stack of the operating system that the browser is built in.
Haskell, by default, provides far less functionality "for free". That is, if you want to display a pop up, you'll have to use some library that allows you to display some pop-up.
This is a much bigger question than it possibly seems. It's very similar to the same question in any other batch-style programming language. How would you do this in Java, or in Ruby? Well, you need to find a library that supports it.
One such library for many languages and that is cross platform across operating systems is wxWidgets. It's built in C++, but there are bindings/libraries for Haskell and many other languages. The Haskell library is called wxhaskell: https://wiki.haskell.org/WxHaskell
Good luck, and don't expect it to be an easy path necessarily.
If you have interest in learning Haskell basics, feel free to take a look at this tutorial I helped author: http://happylearnhaskelltutorial.com
I would like to use a text-based UI in my Haskell program. I found some bindings for the ncurses library (see also hscurses or ncurses, which one to use?). The hscurses and nanocurses packages are just simple wrappers around the C library, while vty isn't very well documented and a bit ugly (for example mixing snake_case and CamelCase).
The ncurses library on Hackage looks much more pretty and provides API which nicely fits Haskell. The problem is that it doesn't seem to implement some crucial features, like resizing or refreshing the windows.
So my question is:
is there any other Haskell text UI library, either ncurses-based or not, which I missed?
if there isn't anyone, is it possible to extend the ncurses Haskell library to at least support window refreshing and resizing? (this should be probably consulted with the project owner, but I need the solution quickly)
EDIT:
I finally used nscurses without windows (and panels) to avoid the troubles with refreshing them. I had problems with output to bottom-right corner of a window (a very similar issue was reported for Python's ncurses binding). I solved it by not writing there :).
Have you looked at vty-ui? It has a very nice user manual with lots of examples. I believe it's essentially a wrapper around vty.
I've used nanoncurses and hscurses succesfully, my hmp3 app has a binding that was the basis for nanocurses.
No matter what you probably will want a nice high level API. hscurses does have a box abstraction at least.
You'd be fine going with hscurses.
There is another good choice for Text-based user interfaces in haskell;
Brick is written by jtdaugherty, the same person that developed vty-ui which is Deprecated now.
The API is Declarative, which is Better for Presenting a language like Haskell.
also the Documentation was great and complete.
In Common Lisp, programs are often produced as binaries with a translator bundled inside. StumpWM is a good example.
How would one do the same with Haskell and OCaml?
It is not necessary to provide a debugger as well, as Common Lisp does, the aim is to make extensions while not depending on the whole translator package ( xmonad which requires GHC ).
P.S. I know about ocamlmktop, and it works great, except I don't really get why it requires "pervasives.cmi" and doesn't bundle it with the binary. So, best thing I can do is mycustomtoplevel -I /path/to/dir/with/pervasives.cmi/. Any way to override it?
This isn't really possible for (GHC) Haskell - you would either need to to ship the application binary + GHC so you can extend via GHC-API, or embed an extension language. I don't think there are any "off-the-shelf" extension languages to embed in Haskell at the moment, though HsLua might be close. This is a bridge to the the standard (C source) Lua. There was a thread on Haskell-cafe last month about extension languages written in Haskell, I think the answer was 'there aren't any'.
http://www.haskell.org/pipermail/haskell-cafe/2010-November/085830.html
With GHC, there is GHC-API, which allows you to embed ghci-like interpreters in your program. It's a quite low-level and often changing library, since it simply provides access to GHC internas.
Then, there is Hint, a library which aims to encapsulate ghc-api behind a well designed and more stable interface.
Nevertheless, I've recently switched from using either of these packages to using an external ghci. The external ghci process is controlled via standard input/output pipes. This change made it easy to stay compatible with GHC 6.12.x and 7.0.x, while our ghc-api code broke with GHC 7.x and hint didn't work out of the box either. I don't know whether there is a new version of hint available, which works with GHC 7.
For Ocaml, have you tried using findlib? See the section Custom Toploops.
Is there a programming language which can be programmed entirely in interactive mode, without needing to write files which are interpreted or compiled. Think maybe something like IRB for Ruby, but a system which is designed to let you write the whole program from the command line.
I assume you are looking for something similar to how BASIC used to work (boot up to a BASIC prompt and start coding).
IPython allows you to do this quite intuitively. Unix shells such as Bash use the same concept, but you cannot re-use and save your work nearly as intuitively as with IPython. Python is also a far better general-purpose language.
Edit: I was going to type up some examples and provide some links, but the IPython interactive tutorial seems to do this a lot better than I could. Good starting points for what you are looking for are the sections on source code handling tips and lightweight version control. Note this tutorial doesn't spell out how to do everything you are looking for precisely, but it does provide a jumping off point to understand the interactive features on the IPython shell.
Also take a look at the IPython "magic" reference, as it provides a lot of utilities that do things specific to what you want to do, and allows you to easily define your own. This is very "meta", but the example that shows how to create an IPython magic function is probably the most concise example of a "complete application" built in IPython.
Smalltalk can be programmed entirely interactively, but I wouldn't call the smalltalk prompt a "command line". Most lisp environments are like this as well. Also postscript (as in printers) if memory serves.
Are you saying that you want to write a program while never seeing more code than what fits in the scrollback buffer of your command window?
There's always lisp, the original alternative to Smalltalk with this characteristic.
The only way to avoid writing any files is to move completely to a running interactive environment. When you program this way (that is, interactively such as in IRB or F# interactive), how do you distribute your programs? When you exit IRB or F# interactive console, you lose all code you interactively wrote.
Smalltalk (see modern implementation such as Squeak) solves this and I'm not aware of any other environment where you could fully avoid files. The solution is that you distribute an image of running environment (which includes your interactively created program). In Smalltalk, these are called images.
Any unix shell conforms to your question. This goes from bash, sh, csh, ksh to tclsh for TCL or wish for TK GUI writing.
As already mentioned, Python has a few good interactive shells, I would recommend bpython for starters instead of ipython, the advantage of bpython here is the support for autocompletion and help dialogs to help you know what arguments the function accepts or what it does (if it has docstrings).
Screenshots: http://bpython-interpreter.org/screenshots/
This is really a question about implementations, not languages, but
Smalltalk (try out the Squeak version) keeps all your work in an "interactive workspace", but it is graphical and not oriented toward the command line.
APL, which was first deployed on IBM 360 and 370 systems, was entirely interactive, using a command line on a modified IBM Selectric typewriter! Your APL functions were kept in a "workspace" which did not at all resemble an ordinary file.
Many, many language implementations come with pure command-line interactive interpreters, like say Standard ML of New Jersey, but because they don't offer any sort of persistent namespace (i.e., when you exit the program, all your work is lost), I don't think they should really count.
Interestingly, the prime movers behind Smalltalk and APL (Kay and Iverson respectively) both won Turing Awards. (Iverson got his Turing award after being denied tenure at Harvard.)
TCL can be programmed entirely interactivly, and you can cetainly define new tcl procs (or redefine existing ones) without saving to a file.
Of course if you are developing and entire application at some point you do want to save to a file, else you lose everything. Using TCLs introspective abilities its relatively easy to dump some or all of the current interpreter state into a tcl file (I've written a proc to make this easier before, however mostly I would just develop in the file in the first place, and have a function in the application to resources itself if its source changes).
Not sure about that, but this system is impressively interactive: http://rigsomelight.com/2014/05/01/interactive-programming-flappy-bird-clojurescript.html
Most variations of Lisp make it easy to save your interactive work product as program files, since code is just data.
Charles Simonyi's Intentional Programming concept might be part way there, too, but it's not like you can go and buy that yet. The Intentional Workbench project may be worth exploring.
Many Forths can be used like this.
Someone already mentioned Forth but I would like to elaborate a bit on the history of Forth. Traditionally, Forth is a programming language which is it's own operating system. The traditional Forth saves the program directly onto disk sectors without using a "real" filesystem. It could afford to do that because it didn't ran directly on the CPU without an operating system so it didn't need to play nice.
Indeed, some implementations have Forth as not only the operating system but also the CPU (a lot of more modern stack based CPUs are in fact designed as Forth machines).
In the original implementation of Forth, code is always compiled each time a line is entered and saved on disk. This is feasible because Forth is very easy to compile. You just start the interpreter, play around with Forth defining functions as necessary then simply quit the interpreter. The next time you start the interpreter again all your previous functions are still there. Of course, not all modern implementations of Forth works this way.
Clojure
It's a functional Lisp on the JVM. You can connect to a REPL server called nREPL, and from there you can start writing code in a text file and loading it up interactively as you go.
Clojure gives you something akin to interactive unit testing.
I think Clojure is more interactive then other Lisps because of it's strong emphasis of the functional paradigm. It's easier to hot-swap functions when they are pure.
The best way to try it out is here: http://web.clojurerepl.com/
ELM
ELM is probably the most interactive you can get that I know of. It's a very pure functional language with syntax close to Haskell. What makes it special is that it's designed around a reactive model that allows hot-swapping(modifying running code(functions or values)) of code. The reactive bit makes it that whenever you change one thing, everything is re-evaluated.
Now ELM is compiled to HTML-CSS-JavaScript. So you won't be able to use it for everything.
ELM gives you something akin to interactive integration testing.
The best way to try it out is here: http://elm-lang.org/try