Hello,

Pascal was designed for teaching. I'm sure everyone knows this.

The chairman of the Free Pascal & Lazarus foundation (and me) take this to heart: we would very much like to reintroduce pascal in schools. While it is not certain that we will achieve success, we still try to improve the teaching experience for pascal.

Some languages allow you to test the language on a website. No need to install anything.

We can make the same possible for Pascal.

To this end, I've been working on a project for some time now:

https://live.freepascal.org/

A live editor for pascal, allowing you to run pascal in the browser. It uses pas2js for 'compiling' and lazarus' JCF (compiled to wasm) for formatting the code. You can also pick files from your local computer.

It features a JIT compiler: if you don't do anything for 3 seconds or more, it will compile in the background and annotate the code in the gutter with errors/warnings etc.

You can embed the editor in an existing page and control it from the enveloping page:

https://live.freepascal.org/test-embed.html

The idea is to enable a self-paced tutorial:

https://live.freepascal.org/tutorial-sample.html

But also to have specific assignments:

http://live.freepascal.org/?assignment=assignments/hello-world.json

The latter would be useful for a teacher.

The page tries to verify the results, and gives hints (all pre-configurable).

I know that some people are trying to put together a tutorial. It is my hope that they will consider integrating this in their tutorial.

On the server, it is just a set of static files, so no heavy load. Unzip, and you are ready to go.

I will be committing the code for this in a repo once I've cleaned up a bit.

Some embryonal ideas for improvements:
- Step-by-step tutorial mode with manifest
- Tutorial progress persistence
- Submit results to teacher endpoint (will need server support)
- Multi-file tabbed editor
- Read-only code regions for scaffolded exercises
- Inline hover annotations / code docs (AKA: code insight, the pascal LSP compiled to wasm should enable this)
- Welcome overlay
- Contextual "what next?" guidance
- Quick-insert code snippets
- Unit catalog grouped by domain
- Resizable split panes (draggable divider)
- Separate console panel from DOM output
- Resizable output iframe + presets
- Use FPC itself to output wasm.

Other suggestions for improvements are welcome.
Contributions as well, obviously.

The page is an initial version, so be kind in your judgment :-)

Michael.

On 2026-02-23 10:50, Michael Van Canneyt via fpc-pascal wrote:

Hi Michael,

Pascal was designed for teaching. I'm sure everyone knows this.

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The page is an initial version, so be kind in your judgment :-)

For start, it would be nice to get the following error fixed ( ;-) ) :

Failure: failed to compile program, please check error messages. Info: MainSrcFile /tmp/main.pp -> /tmp/main.pp
Info: Formatpath /tmp/main.pp -> tmp/main.pp
Info: Parsing tmp/main.pp ...
Info: ExpandFileNamePJ /tmp/main.pp Extract file name : main.pp Fatal: Read error "/tmp/main.pp"
Fatal: Compilation aborted

(Appears when trying to compile one of the provided examples)

Tomas

Great! Bookmarked.

El Mon, 23 Feb 2026 10:50:31 +0100 (CET)
Michael Van Canneyt via fpc-pascal

Which one ? I tried all, and they all worked ?

Maybe a sync error. That would be difficult to trace. I did tests in the browser with 3G throttling, and it still worked, so I'm a bit at loss to explain this.

Michael.

Michael Van Canneyt wrote

Hello, Pascal was designed for teaching. I'm sure everyone knows this.

The essence of it is to learn abstract thinking. And for that purpose, it is better to read the Wirth Report than to play around with a compiler .....

Regards,

Adriaan van Os

On Feb 23, 2026 at 4:50:31 PM, Michael Van Canneyt via fpc-pascal <

Compile/Run button is disabled and I see "Loading units 11/15...". macOS and Safari. Works on Chrome though so it's browser related.

Ah, always refreshing to read encouraging comments.

Michael.

Michael Van Canneyt wrote

On Mon, 23 Feb 2026, Tomas Hajny via fpc-pascal wrote: > On 2026-02-23 10:50, Michael Van Canneyt via fpc-pascal wrote:

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I tried again now, the result is the same (64-bit Firefox running on MS Windows at the moment). It already happened with the first example loaded by default (i.e. "Hello World"), but I got the same when trying "String operations" demo as well. Attached you'll find export from the browser console - feel free to ask if there's anything else I could provide. I tried reloading the page using F5 key -> no difference.

Tomas

I'm guessing the wasm is too complicated for safari. Any errors in the developer console ?

Michael.

Well, it seems related to your browser:

"uncaught exception: out of memory 7"

Do you have some safety mechanisms in place ?

Michael.

Compile/Run button is disabled and I see "Loading units 11/15...". macOS and Safari. Works on Chrome though so it's browser related.

Same here with FF (147.0.4) on Win11 (well, 13/15 instead of 11/15)

Same here with FF (147.0.4) on Win11 (well, 13/15 instead of 11/15)

Sorry: 1215...

Any errors in the developer console ?

How to access that?

Michael Van Canneyt wrote

On Mon, 23 Feb 2026, Tomas Hajny via fpc-pascal wrote:

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Like? I use uBlock Origin extension, but it didn't block anything on that page and I tried also reloading the page after disabling this extension. The default browser on this machine is MS Edge and potential GPO enforced security settings are more likely to be in place for that one - but it works there (as I realized now). If I open the page in an anonymous window of Firefox, it also shows the out of memory error in the browser console, but it breaks even before getting to the point of enabling the buttons, i.e. I see "Loading compiler..." and the buttons are disabled. I guess that there should be some mechanism for the page to demand more memory from the browser and it probably asks for less than what is necessary on both Firefox and Safari (whereas it works in Chrome derived browsers apparently). Interestingly, it works from Firefox running on a mobile phone (Android). So yes, it's likely related to the browser, but that doesn't necessarily mean that I could or should fix it on my side...

Tomas

F12

Tomas

> Any errors in the developer console ? How to access that?

Never mind....

On Feb 23, 2026 at 10:56:24 PM, Michael Van Canneyt via fpc-pascal <

yeah seeing 4 things similar to this:

Failed to load resource: the server responded with a status of 404 (Not Found) and then: https://live.freepascal.org/wasmcompiler.js.map

which is indeed giveing a 404. If I open that in Chrome it gives a 404 too though. 🤷

Michael Van Canneyt via fpc-pascal said on Mon, 23 Feb 2026 10:50:31 +0100 (CET)

Very cool! Next step: Make it more discoverable by placing an index.html or whatever index you need to place at
http://live.freepascal.org/?assignment=assignments or http://live.freepascal.org/assignments . A person unfamiliar with your website needs to be able to random access all assignments.

Once again, this is a great way to gently introduce Pascal and show that it's not some ancient difficult language. Congratulations on a job well done!

SteveT

Steve Litt

http://444domains.com

Michael Van Canneyt via fpc-pascal said on Mon, 23 Feb 2026 16:16:50 +0100 (CET)

Program StringOps failed with following message:

============================
Info: Formatpath /tmp/main.pp -> tmp/main.pp
tmp/main.pp(14,26) Error: identifier not found "ReverseString" Fatal: Compilation aborted
============================

I commented out the line that called ReverseString and it succeeded.

Just in case it was a UTF-8 that looked like Ascii "ReverseString", I deleted and retyped "ReverseString", and it failed the same way.

Was this program supposed to define a function called ReverseString()?

SteveT

Steve Litt

http://444domains.com

Adriaan van Os via fpc-pascal said on Mon, 23 Feb 2026 15:38:24 +0000 (UTC)

I couldn't disagree more. We must crawl before we can walk. I guarantee that reading any text by Wirth will bore 99% of all humans to the point where they'll quit in a half hour. Wirth was a lousy writer.

Live Pascal can get somebody excited enough to put up with Wirth.

SteveT

Steve Litt

http://444domains.com

Bart via fpc-pascal said on Mon, 23 Feb 2026 17:08:35 +0100

Here are my results using 64 bit Void Linux:

Chromium: Works

Firefox: Works

Vivaldi: Works

Eolie: Stalls at "Loading unit 13/15"

Otter Browser, Surf, Netsurf, stalls on "Loading Compiler"

Qutebrowser: Loads all units, but compile button inoperable (has an international "forbidden" sign as the mouse icon).

HTH,

SteveT

Steve Litt

http://444domains.com

I'm still working on a document that describes how it all works, and how you can use it. That will be placed in a separate page on the site, obviously.

Once again, this is a great way to gently introduce Pascal and show that it's not some ancient difficult language. Congratulations on a job well done!

Thank you!

Michael.

No, I simply failed to put the correct example-manifest.json on the site, in which I deleted the line. (I silently cursed myself when I read your mail :/)

Should be OK now. I still need to put a cache-buster or no-cache header in place...

As said, it is a first version.
No doubt many fine-tuning changes and fixes will follow...

Michael.

All 404s should be fixed. map files and favicon.ico - should have no influence on the working though.

Michael.

Hi!

Am Montag, dem 23.02.2026 um 11:27 -0500 schrieb Steve Litt via fpc- pascal:

This function seems to be in StrUtils, not SysUtils, but that unit is not in the library. I couldn't get it to work either.

Bye
Hansi

No, but without knowing the cause there is little I can do...

I use firefox only, and it has worked all through the development cycle. I also use uBlock origin. I was on a linux, though I don't see how that would matter.

The good news is: I can reproduce the issue in Safari: it fails with a 'out of memory' So I'll do some testing on safari. First web search is not making me optimistic, seems safari and wasm are not a happy couple.

Michael.

Yes, this is why I removed the function. I didn't want to add another file. But it is on my todo list to add more standard units, I want to make it server-configurable.

Michael.

On 2026-02-23 21:26, Michael Van Canneyt via fpc-pascal wrote:

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I can confirm that Firefox running on Linux Debian runs the site without issues. It might be useful to mention, that the Firefox version on my Debian is 140.7.0esr (standard version included with the installed distribution - currently on Debian 12.12), whereas the latest MS Windows version is 147.0.4.

On my Linux machine, I can reproduce the issue with Seamonkey (installed from Debian repository available on
http://downloads.sourceforge.net/project/ubuntuzilla/mozilla/apt). The information provided in the browser console is:

Will-change memory consumption is too high. Budget limit is the document surface area multiplied by 3 (1153920 px). Occurrences of will-change over the budget will be ignored.
live.freepascal.org
Instantiating of WebAssembly from pas2js.wasm failed wasm validation error: at offset 130: bad type
pas2jsworker.js:5350:17
p2js_loadfiles failed with code -4 , message: ZenFS is not defined wasmcompiler.js:3778:15

Maybe this helps?

Tomas

Well, that is very limited. The memory is limited to 3Mb ? That's ridiculous, I ask of course it fails at once...

the budget will be ignored. live.freepascal.org Instantiating of WebAssembly from pas2js.wasm failed wasm validation error: at offset 130: bad type

That error means the wasm engine of the browser is too old.

Yes, in the sense that it makes clear why it fails, but there is little I can do if memory is so limited.

Wasm is meanwhile quite established, if seamonkey does not support it: again, little I can do about that.

(pas2js can be compiled to Javascript, but this is quite slow)

I'll add a message to the page saying that a "recent standards"-compliant browser is needed.

Thanks for testing this !

Michael.

For me, with the default "Hello world" program loaded, it seems getting stuck at "Loading unit 3/15". That is on Windows 10, with Firefox 147.04

Just tried it on my Linux Mint 22 laptop, and there it works fine, same version of Firefox (147.04)

Both machines have 8GB of RAM (i7 and i5 respectively)

On my programming laptop (16GB RAM, i7), though a lot of tabs open in Firefox (also 147.04), it gets stuck at Loading units 7/15. This is also Windows 10.

hth,

Ralf

On 2026-02-23 22:10, Michael Van Canneyt via fpc-pascal wrote:

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> Instantiating of WebAssembly from pas2js.wasm failed wasm validation > error: at offset 130: bad type That error means the wasm engine of the browser is too old.

OK - admittedly, that SeaMonkey corresponds to Firefox/128.0 engine, which is not exactly the latest... ;-) I just tried to check whether I could reproduce the issue on Linux as well.

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Yes, in the sense that it makes clear why it fails, but there is little I can do if memory is so limited.

I have no idea if the memory limits may be somehow increased. But if not
- OK, so be it.

OK - however, that doesn't clarify the case of the latest Firefox on MS Windows then...

Tomas

I am also on Windows 11 (16 GB RAM) + Firefox 140.7.1esr and I am stuck on "Loading units 5/15 ..." and in developer console I see: "uncaught exception: out of memory"

-Laco.

Hm...

A pattern emerges: the memory issues are caused on windows in firefox. There must be some reason for this. I will investigate.

Michael.

Op 24-2-2026 om 08:57 schreef Michael Van Canneyt via fpc-pascal:

The hello world compiles and runs for me on Windows 11 (64GB RAM)  Firefox 147.0.4

(note also slightly newer firefox, 147 vs 140)

Then again, I have exactly the same new version of FF 147.0.4 on the Windows 11 machine as well (still ending up with "not enough memory"). Admittedly, I have quite a few browser tabs open. However, I have 32 GB RAM installed and only something like 40% of that used (equally before and after accessing the live.freepascal.org site).

Tomas

My Firefox (under win 10 / Europe still gets OS updates)

Loading the page adds 250 to 300MB (300 according to Taskmanager, approx // 250 according to FF about:memory compare measurements) Running "compiling world" adds another 50 to 100.
Repeated compiling does not further increase it (in task mgr)

And having Firefox idle seems to reduce memory usage (while the tab stays open) by most of it after a while.

Chrome  adds (task mgr) 100 MB to load the page and 100 to compile.

When I open the settings, and do "enable jit compiler" then it takes 5 seconds and gives me out of mem.

I did not see memory consumption raise during the 5 secs. So it likely was one sudden big alloc attempt.

After that compilation would not work : error empty string / file not found tmp/main

reloading the page and it works again, until I do enable jit again

Op 24-2-2026 om 12:09 schreef Martin Frb via fpc-pascal:

I did this too, and when enabling jit a compile also fails after:

Info: MainSrcFile /tmp/main.pp -> /tmp/main.pp
Info: Formatpath /tmp/main.pp -> tmp/main.pp
Info: Parsing tmp/main.pp ...
Info: ExpandFileNamePJ /tmp/main.pp Extract file name : main.pp Fatal: Read error "/tmp/main.pp"
Fatal: Compilation aborted

On Tue, Feb 24, 2026 at 9:57 AM Michael Van Canneyt via fpc-pascal <

Windows 11 Enterprise + MS Edge 145.0.3800.70 => all examples work.

On Feb 24, 2026 at 1:52:01 AM, Michael Van Canneyt via fpc-pascal <

Cool Chrome works now but not Safari.

It says "p2js_loadfiles" failed with code "-4", message: ""Out of memory""

from line 4680 in wasmcompiler.js:

            console.log(aResult.initialCommand, " failed with code ",
aResult.errorCode, ", message: ", aResult.errorMessage);

I know, I am investigating this (using Safari). It is proving elusive.

Michael.

Same for me.

It works fine on Firefox 147.0.4 (64 bits) on Lubuntu 25.10 with no message in the console

But it fails on Firefox 148.0 (64bits) on Windows 11 Pro Loading units 5/15...

Messages in console:
Erreur dans les liens source : request failed with status 404 URL de la ressource : null
URL du lien source : installHook.js.map
uncaught exception: out of memory | 10 | pas2jsworker.js:6382:16 (in function LoadFile)

Well, I have some fixes which *may* help for firefox. I need to put up a test page so people can test it.

I've given up on Safari, that browser needs to be euthanized. Even the smallest wasm program fails :/

Michael.

On the forum, member ALLIGATOR says he hunted it down to a bug in FF: https://bugzilla.mozilla.org/show_bug.cgi?id=2019323

See the forum: https://forum.lazarus.freepascal.org/index.php/topic,73547.0.html

Thank you, it has been very useful:

Since they mentioned the ZenFS fix for allocating too much memory, I updated ZenFS (an adventure in itself).

Can firefox users who experienced a fail please test this version:

https://live.freepascal.org/test-firefox

I tested whether it works in Safari, and the answer is YES! Which is a big relief...

If I get confirmation that the fix also works in Firefox, I will put the new version in place on the main page.

Some other goodies are also forthcoming :)

Michael.

Hi Michael,
there is some progress in my use case: "Loading units 15/15..." and in console i see errors:
- Failed to create webassembly. Reason: pas2jsworker.js:5538:17
- Error: no WebAssembly compiler available
    ArrayOK https://live.freepascal.org/test-firefox/pas2jsworker.js:5388 pas2jsworker.js:5539:17
- Error: no WebAssembly compiler available pas2jsworker.js:5388:30

-Laco.

Michael Van Canneyt wrote

On Wed, 25 Feb 2026, Bart via fpc-pascal wrote: > On Wed, Feb 25, 2026 at 10:53 AM Michael Van Canneyt via fpc-pascal > wrote:

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Yes, I can confirm that it works now with FF on MS Windows. :-)

Tomas

As far as I can tell, it means your firefox has wasm disabled.

about:config

Check the javascript.options.wasm setting or wasm_baselinejit settings. They should be 'true'

Michael.

Great, I'll move the new version in place then.
Thanks for testing!

Michael.

Yes there was: javascript.options.wasm_baselinejit=False, after I changed it to True it works as expected :-)
Thanks.
-Laco.

Can firefox users who experienced a fail please test this version:

I can compile and run the "Hello World" program now (FF 148.0 on Win11). Did not test other examples yet.

I have updated the site. New features:

- Safari and Firefox on windows should now work.
(you may need to clear the browser cache)

- Code templates ('snippets') - has Ctrl-J shortcut (as in Lazarus, I believe)

- You can now configure your own examples and snippets.

- Help page at https://live.freepascal.org/help.html

- Embedding guide at https://live.freepascal.org/embed-guide.html

Both help pages are reachable from the main page.

I put the sources for the site online:

https://gitlab.com/freepascal.org/fpc/live-pascal

It uses a Creative Commons CC0 license, for those that are into licenses. (Gitlab forces you to put a license, and CC0 comes closest..)

I'll update with new some new features one by one. Suggestions always welcome.

Michael.

Michael Van Canneyt wrote

Pascal was designed for teaching. I'm sure everyone knows this. ... snip ... To this end, I've been working on a project for some time now:

Well done Michael! I love this idea.

I did a quick test and could compile and run all the examples.

Regards,
- Graeme -