David Mertens

App::Prima::REPL Help

This is the help documentation for App::Prima::REPL, a graphical run-eval-print-loop (REPL) for perl development, targeted at pdl users. Its focus is on PDL, the Perl Data Language, but it works just fine even if you don't have PDL.

At the bottom of the App::Prima::REPL window is a single entry line for direct command input. The main window is a set of tabs, the first of which is an output tab. Additional tabs can contain files or any other extension that has been written as a App::Prima::REPL tab.

If your project has project-specific notes, you should be able to find them either here: prima-repl.initrc or here: prima-repl.initrc.pl.

Fixing Documentation Fonts

If your documentation fonts look bad, you can change them by going to View->Set Font Encoding.

Basic Navigation

Before I launch into the tutorial, I want to cover some basic navigation to help you quickly get around the REPL. The following keyboard shortcuts should be helpful to you even as we get started:

 Normal Keyboard  Mac Laptop
 CTRL-h           CTRL-h        open or switch to the help window
 ALT-1            ??????        go to the output window
 CTRL-i           CTRL-i        put the cursor in the input line
 CTRL-PageUp      CTRL-FN-Up    go to the previous tab
 CTRL-PageDown    CTRL-FN-Down  go to the next tab


These are a collection of tutorials to get you started using the Prima REPL. Except for the first tutorial, text that you should enter will be prefixed with a prompt like >.

Basic Output

Our first exercise will be getting basic output from the REPL. Enter the following into the input line, but don't press enter yet:

 print "Hello!"

Take note of the last line of text in the output window, then press enter. You should see the following appear on your output screen:

 > print "Hello!"

What happens if you type an expression like 1+1? If you just type the expression in the input line, you will see this as output:

 > 1+1

Why didn't it print 2? It didn't print 2 because you didn't ask it to print 2. You can easily accomplish that by using the print function, or its abbreviation p. Type the following in the input line:

 p 1+1

The output should look like this:

 > p 1+1

You may be used to REPLs that print out the result of whatever action you just took. This REPL does not do that because it is geared towards PDL use, and the output for PDL can get exceedingly long. Rather than always print potentially long results to the output, the Prima REPL is quiet by default and makes it easy to print your results if you want.

Finding Documentation

Prima REPL uses Prima's built-in pod viewer (which you may be using to view this documentation). If you have the help window open, you can look at a particular module's documentation by pressing g on your keyboard. A dialog will ask for the name of the module with the documentation you want to read and will open that module if it manages to find it.

There are two additional commands for finding and viewing help. The first is the help command. By itself, the help command brings up the documentation for Prima REPL. (Pressing CTRL-h accomplishes the same thing.) However, you can also specify the name of a module with documentation:

 > help Carp

This command will open the pod viewer with the requested module's documentation. This is sometimes preferable to pressing g from Prima's help window, since if you have a typo in your module name you must retype the whole thing. The input line remembers what you last typed, so it's easy to retrieve the correct typos.

If you have PDL, you can also use the pdldoc command, which operates similarly to the pdldoc program on your computer. Typing

 > pdldoc hist

will load the pod from PDL::Basic and scroll to the documentation for the hist function and typing

 > pdldoc Ufunc

will load the pod from PDL::Ufunc into the pod viewer.

If you need help on Perl, Prima, or PDL, check out perlintro, Prima::tutorial, or PDL::QuickStart, respectively.

One caveat to the help command: if the pod viewer's current page has a section with the text that you type into help, the viewer will scroll to that section instead of opening that module's documentation. The only way to go to that modules documentation is to go to some other page, then enter the name of the module with the documentation you want to read.

Multi-line Input

The input line at the bottom of the window only allows for single-line entry. However, sometimes it's better to work with many lines at once, such was when you're writing a nontrivial for-loop or subroutine. You can do this with a file buffer. To can create a new file buffer, pressing CTRL-n or type new_file. This will open a new tab called "#2".

Try putting the following code in that new tab:

 print "Hello from the file buffer!\n";
 # This is a comment. Any valid Perl is allowed in file buffers.
 print "OK, that's all, folks!\n";

To execute the contents of the file buffer, switch to the input line by pressing CTRL-i (which toggles between the buffer and the input line) and typing

 > run_file

It will probably seem like nothing happened. However, the contents of the print statement were sent to the Output tab, so go there by clicking on the tab with your mouse or pressing ALT-1. You'll see the following in your output window:

 > run_file
 Hello from the file buffer!
 OK, that's all, folks!

Running the contents of a file buffer is useful enough that it has two keyboard shortcuts. The first is CTRL-Enter, which runs the code but keeps you on your current file buffer. The second is CTRL-SHIFT-Enter, which switches you to the Output tab before it begins executing the code.

The output window knows how to handle carriage returns (\r) as well as newlines (\n). For an example, put the following in your buffer and hit CTRL-SHIFT-Enter:

 for(1..10) {
   print "\r$_";
   sleep 1 unless $_ == 10;
 print "\nAll done!\n";

That should take about 10 seconds to run and the numbers should overwrite each other in the process. This is very useful if you have a long-running process and you want to print the status without filling up the output window with redundant lines. Furthermore, the Output tab displays all text sent to Perl's STDIO and STERR file handles. (I had hoped that even text from low-level processes that normally print to the screen, such as C code that uses printf, would display their results to the Output tab, but no such luck. I'm researching how to properly print stuff from Inline::C code and hope to update this soon.)

Note that the input line is greyed out while the code executes, so if you have a long-running process, you will not be able to type in new commands or even switch tabs.

Editing Files

Although the multi-line buffer is not the greatest editor, it is useful in a pinch. You can save the contents of a buffer by pressing CTRL-s in the buffer window, which will present a dialog asking where you want to save your file. Alternatively, you can type

 > save_file 'filename'

at the input line. The filename is optional; if you don't supply one, you will get a dialog box asking for the name of the file, just as if you used the keyboard shortcut.

You can open a file with the open_file function or CTRL-o. You can supply a filename to the function, but if you do not (or if you use the keyboard shortcut), you will get a dialog asking which file you want to open. NOTE: IF YOU ARE CURRENTLY VIEWING A FILE BUFFER, OPENING A FILE WILL OVERWRITE THE CONTENTS OF THE BUFFER. To save yourself from losing the contents of your current buffer, you should either create a new tab first, or switch to the Output tab. Trying to open a file from the Output tab automatically creates a new tab for your file.

Viewing Images

Prima makes opening and viewing images very easy, so I've added a function for opening a tab to display an image. The function is open_image and it requires that you specify the filename of your image to open. For example, if you have an image called test.png in your current working directory, you could view it with the following:

 > open_image 'test.png'

Plotting PDL Data

You can easily plot data with the various plotting commands if you have PDL::Graphics::Prima installed. This will create a new tab with your specified plot (with a special exception that we'll get to shortly). The interface is identical to PDL::Graphics::Prima::Simple, and you should check the documentation in that module for details. Here are some examples to remind you how this works:

 > $t_data = sequence(6) / 0.5 + 1
 > $y_data = exp($t_data)
 > line_plot($t_data, $y_data)

Here's a more complicated example for a multiline buffer. (Note that in future versions of PDL::Graphics::Prima, datasets will be handled differently.)

 # Create some simple data:
 $t_data = sequence(6) / 0.5 + 1;
 $y_data = exp($t_data);
 # Create the plotter widget:
 $plotter = plot(
     -function => ds::Func(\&PDL::exp, color => cl::Blue),
     -data => ds::Pair($t_data, $y_data, color => cl::Red),
     y => {
         scaling => sc::Log,
         label => 'exp(t)',
     title => 'Exponential Curve',
     x => { label => 't' },

This multiline buffer saves the reference to the plotting widget, allowing you to fiddle with it from the input line if you like. For example, you can add the hyperbolic cosine function like so:

 $plotter->dataSets->{cosh} = ds::Func(\&PDL::cosh, colors => cl::Green);


You can use PDL::NiceSlice in your code. It is not terribly intelligent method at the moment. If the evaluator finds the exact string use PDL::NiceSlice, it uses the PDL::NiceSlice preprocessor to replace PDL slices with calls to mslice, just like the real source filter. Unfortunately, this does not look for statements like no PDL::NiceSlice, which can be problematic.


There are a number of ways that you can customize your REPL, including per-project rc files and pod notes, custom tabs, and custom commands.

RC File and Notes

App::Prima::REPL supports per-directory rc files and input logs. When you have a file called prima-repl.initrc or prima-repl.initrc.pl in the directory from which you execute prima-repl, it will be executed upon startup (with a preference for the former). The purpose of this rc file is to allow for per-project initialization and function definitions.

You can emulate user input with the REPL::simulate_run command, which will add text to the input line and then use the standard input lne mechanism to evaluate the text. This can be useful because it puts the evaluated text into the user's history. However, as this adds lines to the history file, you should use this sparingly, only when you think the user will want to retrieve the command in their history.

A very useful apect of initrc file is that you can add documentation by simply inserting pod in your initrc file. The link at the top of this help file will automatically open the documentation or give a message indicating that there is no such documentation. This way, if you declare any useful functions in your initrc file, you can document them easily.

The initrc file can also add tabs and add custom commands, but you can do these from a multiline buffer as well, so I put them in their own sections.

Custom Tabs

If you wish to create custom tabs, there are two commands that will help.

REPL::create_new_tab($name, @creation_options)

This puts a new tab at the end of the tab list with the specified name. The @creation_options are exactly what you would send to Prima's insert command, including the widget class as the first element. This function returns the created object when called in scalar context. In list context, it also returns the tab index as the second return value. This index is useful if you want to specify a different default widget for your tab, which brings me to...

REPL::change_default_widget($index, $widget)

This function changes the default widget for the tab with the given index. The default widget is the widget that recieves the keyboard focus when you first switch to the tab. This function takes the tab index (returned by REPL::create_new_tab in list context) and the desired widget. Note that if you want CTRL-i to toggle between the desired widget and the input line, which is the behavior of the file buffers, you will need to have your default widge properly respond to CTRL-i keyboard input.


Given a normal editor widget, this sets the various options to make the editor behave like the default multiline buffer editor. For example, it turns on syntax highlighting, sets a monospace font, and sets the default accelerator keys. Although not strictly necessary for creating tabs, it may be useful if you want to create a tab with both an editor and some other sort of widget, side-by-side, as is done in App::Prima::REPL::Talk.

This function does not set the widget as the tab's default widget, since you may want the default widget to be something else. You should explicitly invoke REPL::change_default_widget (above) to do that.

The endowed editor has named key bindings that you can overwrite:

 CtrlReturn    CtrlShiftReturn
 CtrlEnter     CtrlShiftEnter
 CtrlPageDown  CtrlPageUp

You can override these commands with something like this:

 # Update ctrl-return/ctrl-edit for the editor
       # Ctrl-Enter runs the file
       ['CtrlReturn', '', kb::Return  | km::Ctrl, $run_code ]
     , ['CtrlEnter', '', kb::Enter    | km::Ctrl, $run_code ]
   , ''
   , 0

At some point I'll add an example of how to use these.

Custom Commands

Perl knows about functions and list operators. App::Prima::REPL also knows about commands, like the help command. Remember, the help command doesn't require quotes around the module name. How do I do this? I achieve this by hooking into the PressEnter stage of the InputHistory widget. Hooking into this stage of the widget lets you modify what eventually gets evaluated (for example, by applying the NiceSlice filter) and even lets you avoid the Perl eval-stage altogether.

Here's the hook that proceses the help command:

 $REPL::inline->add_notification(PressEnter => sub {
     # See if they asked for help.
     if ($_[1] =~ /^\s*help\s*(.*)/) {

Notice that the help command does not want the eventual string to be evaluated, so it calls get_help and then clears the event. If you simply want to modify the string before it gets evaluated, you need to modify $_[1] directly without clearing the event.

The subroutine that you write for such hooks will be passed two arguments, the InputHistory object ($REPL::inline) and the text from the input line's buffer. Note that by the time your notification receives the latter, it may have already been modified as there are a number of built-in notifications.

Other API Functions

Here are some other REPL API functions that you may find useful:


Simply switches the focus to the output tab, which is useful when you want to print a number of things out and have your user notice.

REPL::warn (LIST)

If you simply warn when something goes wrong, the user will probably not notice unless they are looking at the Output tab. This function acts just like Perl's warn function, but it switches to the Output tab, something that should certainly grab your user's attention. Of course, you could use Perl's warn and call REPL::goto_output, but this is faster, especially with failure messages. Compare:

 if ($messed_up) {
     print "Problems!\n";


 return REPL::warn("Problems!\n") if $messed_up;

Indeed, this one-line idiom (return REPL::warn(...) if bad) is quite handy for exiting early upon failure.

REPL::goto_page ($page_number)

Perhaps this should be called goto_tab. Oh well. This switches to the given tab according to the tab's number. Accomodations may some day be made to go to a tab basd on its name.

REPL::goto_next_page =item REPL::goto_prev_page

Simple wrappers around REPL::goto_page that figure out your current page and go to the next or previous one. This is useful if you have multiple tabs that "talk" with each other, so-to-speak.


Running Inline code can be tricky because the code is executed using an eval block. As such, any Inline code should be declared in the use line itself rather than in the __DATA__ or __END__ blocks, as is customary. For example:

 use Inline C => q{
     void my_print_hi() {
         PerlIO_stdoutf("Hello there!\n");

I use the PerlIO function for printing to stdout. In principle, this is supposed to be captured and redirected to the Output tab, but somehow Perl just sends it straight to the terminal. I intend to talk with some experienced XS hackers or the Perl porters about this some time.

PDL Debugging

To get PDL debugging statements, type the following in the evaluation line:

 $PDL::debug = 1

Other keyboard shortcuts

 CTRL-n  create a new multiline buffer
 CTRL-w  close the currently open tab
 CTRL-o  open a file
 CTRL-s  Save a multiline buffer to a file
 ALT-2 through ALT-9 (doesn't work on Mac Laptops)
         switch to tab 2 through 9

Author, Repository

This program is Copyright David Mertens, 2011, 2012. It is distributed under the same terms as Perl itself.

The latest copy of this project should be available on Github at https://github.com/run4flat/App-Prima-REPL.