DEV Community: PabloDevRel

Tabnas: How to define a grammar

PabloDevRel — Sat, 31 Oct 2026 00:05:29 +0000

What is a Grammar?

A grammar is a set of structural rules. Every language has one.

For example, plain English grammar follows a Subject–Verb–Object (SVO) order:

✅ I am Pablo 
❌ Am Pablo I

This is everywhere. In mathematics we also defined a grammar Number symbol Number:

✅ 5 + 6
❌ + 5 6

A snippet of the JSON grammar:

value   = object / array / string / number / "true" / "false" / "null"
member  = string : value
object  = {[  member  *( , member )  ]}
array   = [[  value  *( , value )  ]]

In computing this is very important. If you are going to write a parser of a given format, first it must be clear what the grammar is.

There are thousands of JSON parsers and you can easily write your own since it's well documented.

But what if you're creating your own grammar? Or you want to build a parser of a proprietary and undocumented format?

The Abaqus `.inp` files

Abaqus is proprietary but widely used software that runs finite element simulations in aerospace, automotive, etc.

Abaqus .inp project files are plain text. Anyone can read them in a simple text editor.

For example, this .inp file describes this 🧊 cube:

*HEADING
Single C3D8 hexahedral element - 100 mm cube
*NODE, NSET=NALL
1, 0.0, 0.0, 0.0
2, 100.0, 0.0, 0.0
3, 100.0, 100.0, 0.0
4, 0.0, 100.0, 0.0
5, 0.0, 0.0, 100.0
6, 100.0, 0.0, 100.0
7, 100.0, 100.0, 100.0
8, 0.0, 100.0, 100.0
*ELEMENT, TYPE=C3D8, ELSET=ECUBE
1, 1, 2, 3, 4, 5, 6, 7, 8
*MATERIAL, NAME=STEEL
*ELASTIC
210000., 0.3
*BOUNDARY
1, 1, 3
2, 1, 3
5, 1, 3
6, 1, 3
7, 1, 3
8, 1, 3
*STEP
*STATIC
*CLOAD
3, 3, -1000.
4, 3, -1000.
*END STEP

And yet their language has no official parser or API documentation. There isn't even an official manual we can link: Abaqus keeps theirs behind a paywall, so we work with the documentation of CalculiX, an open-source Abaqus clone that reads the same .inp files. Hundreds of pages of prose, and no grammar in sight: https://dhondt.de/ccx_2.23.pdf

Abaqus .inp parser

We're going to write our own open source .inp files parser library, so anyone can use it to read .inp files and deal with them in their own software.

We take as example our 🧊 cube.inp which starts with the *HEADING. What is this?

Page 527 of the CalculiX manual

OK! Here it is. Now we understand what a HEADING looks like. We can parse it.

Now we do the same with NODE, with ELEMENT, MATERIAL ...
New keyword, open the 800-page PDF manual, define it in the parser, repeat ...

And this with all the keywords, good luck with it and with your tokens.

And what if we want someone else to expand or collaborate with this project? Is this huge PDF manual really the only source of truth for our .inp parsing project? That looks really overkill and costly.

So you know what this project needs, right? A grammar

Tabnas

With Tabnas, we can write the grammar of 🧊 cube.inp in a .abnf file

deck      = *( kwcard / cmtcard / valuecard / blank )
kwcard    = %x2A KWNAME [ KWITEMS ] crlf    
KWNAME    = TX                               
KWITEMS   = %x2C [ KWITEM [ KWITEMS ] ]      
KWITEM    = TX                               
cmtcard   = %x2A %x2A [ 1*( TXTCH ) ] crlf  
valuecard = 1*( TXTCH ) crlf                
TXTCH     = TX / NR / ST / %x2C / %x3A / %x2A
blank     = crlf                             
crlf      = [ %x0D ] %x0A

Every .inp line you will ever see is one of four shapes:

keyword card (*NODE...)
comment card (**...)
data line (1, 0.0, 0.0, 0.0)
empty line.

Check the Tabnas documentation; it explains that block of code completely.

What you can do with your Tabnas Grammar?

1. Validate an `.inp` file

Does this Abaqus .inp file have a valid format?

We run our read-deck-keywords.mjs script against two files: cube.inp, and truncated.inp, which is broken on purpose.

✅ Valid `cube.inp` file

If we run it against our valid 🧊 cube.inp

node read-deck-keywords.mjs cube.inp

Output:

ACCEPTED cube.inp — 29 cards, 9 keywords:
   *HEADING
   *NODE,NSET=NALL
   *ELEMENT,TYPE=C3D8,ELSET=ECUBE
   *MATERIAL,NAME=STEEL
   *ELASTIC
   *BOUNDARY
   *STEP
   *STATIC
   *CLOAD

❌ Invalid `truncated.inp`

But if we run it against the invalid truncated.inp

truncated.inp:

*HEADING
Single C3D8 hexahedral element - 100 mm cube
*NODE, NSET=NALL
1

node read-deck-keywords.mjs truncated.inp

Output:

REJECTED truncated.inp
SyntaxError: [tabnas/unexpected]: unexpected character(s): 1
  --> <no-file>:1:72
  1 | Single C3D8 hexahedral element - 100 mm cube
  2 | *NODE, NSET=NALL
  3 | 1
      ^ unexpected character(s): 1
  4 |
  5 |

  The character(s) 1 do not match any rule alternative active at
  this position.

  --internal: tag=-; rule=_gen1_group~o; token=#NR; plugins=abnf--

The deck is rejected right away and Tabnas tells us exactly where the problem is.

2. Inspect your file keywords

An .inp file can have a lot of noise: data, comments, sets... Maybe for your parser it's interesting to know beforehand which keywords are being used in that .inp file.

With a grammar, extracting every keyword your .inp file uses is a piece of cake:

const tn = new Tabnas({ tokenSet: { IGNORE: ['#SP'] }, comment: { lex: false } })
tn.use(abnf)

// the grammar is in cube.abnf
const abnfSrc = readFileSync('cube.abnf', 'utf8')
const compiled = abnfSrc
  .split('\n')
  .filter((line) => !/^\s*;/.test(line))
  .join('\n')

tn.abnf(compiled)

const file = process.argv[2] ?? 'cube.inp'
try {
  // Filter tabnas parse to detect the different keywords
  const deck = tn.parse(readFileSync(file, 'utf8'))
  const cards = deck.kids.filter(...)
  const keywords = cards.filter(...)
  console.log('ACCEPTED', file, '—', cards.length, 'cards,', keywords.length, 'keywords:')
} catch (e) {
   ...
}

We run it again and the output is the same as demo 1: ACCEPTED cube.inp — 29 cards, 9 keywords:

With this information, anyone can easily tell that:

There are 9 different keywords and 29 cards (recognized lines)
*NODE,NSET=NALL: this deck has a group of nodes, NALL
*ELEMENT,TYPE=C3D8,ELSET=ECUBE: an element of type C3D8 with its connectivity, kept in the set ECUBE
*MATERIAL,NAME=STEEL: a material called STEEL

3. Turn the file into JSON

There's a parser already in Tabnas. We can use it directly with our grammar:

const tn = new Tabnas({ tokenSet: { IGNORE: ['#SP'] }, comment: { lex: false } })
tn.use(abnf)
tn.abnf(compiled) // the grammar, loaded from cube.abnf like in the section above

const file = process.argv[2] ?? 'cube.inp'
const json = tn.parse(readFileSync(file, 'utf8'))
console.log(JSON.stringify(json, null, 1))

The output is very verbose, because the tree is built straight from the grammar: every rule in the .abnf becomes a node ("rule"), every node repeats its raw source text ("src"), and every reused category (TXTCH, crlf) brings its own kid.

node parse-deck.mjs cube.inp

Output

{
 "rule": "deck",
 "src": "*HEADING\nSingleC3D8hexahedralelement-100mmcube\n*NODE,NSET=NALL\n1,0.0,0.0,0.0\n2,100.0,0.0,0.0\n3,100.0,100.0,0.0\n4,0.0,100.0,0.0\n5,0.0,0.0,100.0\n6,100.0,0.0,100.0\n7,100.0,100.0,100.0\n8,0.0,100.0,100.0\n",
 "kids": [
  {
   "rule": "kwcard",
   "src": "*HEADING\n",
   "kids": [
      {"rule": "KWNAME", "src": "HEADING", "kids": []},
      {"rule": "crlf","src": "\n","kids": []}
   ]
  },
  {
    "rule": "valuecard","src": "SingleC3D8hexahedralelement-100mmcube\n","kids": [
      {"rule": "TXTCH","src": "Single","kids": []},
      {"rule": "TXTCH","src": "C3D8","kids": []},
      {"rule": "TXTCH","src": "hexahedral","kids": []},
   ...

Why a grammar?

Why not just write a parser from the PDF documentation?

Because the parser you would write from the PDF is exactly what a grammar gives you:

Lightweight and reliable source of truth

If you write a parser, you don't want yourself or your agents to keep reopening the 800-page PDF for every keyword. It's a mess: your agents might hallucinate, and they will burn a lot of tokens to rebuild context that a 10-line grammar file provides in one shot.

In this project, the same cube.abnf is the backbone of all three tools you saw above: validation, keyword inspection and JSON parsing.

Error proof

This adds a security layer because the grammar is executable: validation is a one-liner, tn.parse(...).

In a pipeline (or an agent session) that touches hundreds of .inp files, this mechanism detects errors early and in a deterministic way.

Adding a keyword does not touch the grammar

The grammar is keyword-agnostic by design: *ANYTHING, PARAM=VALUE is already a valid keyword card, whatever the name is.

Production .inp files use dozens of keywords and new ones show up every release; a new keyword becomes a new case, not a grammar update.

Are there other tools to generate a grammar?

There are many: ANTLR, PEG.js and its maintained fork Peggy ... I checked Ohm and spotted very interesting things in this library.

Ohm vs Tabnas

Maturity

To begin with, this project has 11 more years of history behind it: the repository dates to May 2015, it has 5.5k stars and 48 open issues, and it was last updated this June. Tabnas is the opposite case: its first published npm package appeared in June 2026, so the Tabnas ecosystem is a few months old.

The webpage

Their webpage explains well what it does. I did not completely understand what the Tabnas project is and what a grammar does for it until I saw the awesome Ohm editor.

At a glance you can clearly see what a grammar is and how this library works. Clear and simple.

The Tabnas homepage, on the other hand... it's just hard.

It asks the reader to handle complex phrases like "behaviour binds out of band, through names the compiler already assigns"

Every term is eventually defined, but the buzzwords are just too much at once. If you are not already familiar with this style of grammar tool, you read the docs very slowly.

The Docs and How to sections don't help much at the beginning; they just add more noise.

Something I have to say is, after understanding the grammar context, and especially after learning from Ohm's webpage, I came back to Tabnas and everything was much clearer. So I'd say this is not for beginners.

Another positive thing to say is that the agents understood Tabnas quickly and could build the grammar and the examples of the Abaqus .inp file in seconds, and they helped me to understand what this is.

The syntax

The syntax of Ohm is really clear. This is a definition of some basic arithmetic operations:

In Ohm:

Arithmetic {
  Exp
    = AddExp

  AddExp
    = AddExp "+" MulExp  -- plus
    | AddExp "-" MulExp  -- minus
    | MulExp

  MulExp
    = MulExp "*" ExpExp  -- times
    | MulExp "/" ExpExp  -- divide
    | ExpExp

  ExpExp
    = PriExp "^" ExpExp  -- power
    | PriExp

  PriExp
    = "(" Exp ")"  -- paren
    | "+" PriExp   -- pos
    | "-" PriExp   -- neg
    | ident
    | number

  ident  (an identifier)
    = letter alnum*

  number  (a number)
    = digit* "." digit+  -- fract
    | digit+             -- whole
}

The same in abnf:

Exp       = AddExp

AddExp    = AddExp PLUS MulExp / AddExp MINUS MulExp / MulExp     ; plus | minus | mul-level
MulExp    = MulExp STAR Exps / MulExp SLASH Exps / Exps            ; times | divide | pow-level
Exps      = PriExp CARET Exps / PriExp                            ; power (tightest, right-assoc)

PriExp    = LP Exp RP / PLUS PriExp / MINUS PriExp / name / number

name      = TX                        ; an identifier (engine text token)
number    = NR

PLUS      = %x2B                      ; +
MINUS     = %x2D                      ; -
STAR      = %x2A                      ; *
SLASH     = %x2F                      ; /
CARET     = %x5E                      ; ^
LP        = %x28                      ; (
RP        = %x29                      ; )

In my opinion, Ohm is friendlier to humans because its grammar has more readable labels (-- plus, -- times) and the editor runs a live parse next to your grammar, which makes the feedback loop instant.

Conclusion

The idea behind Tabnas holds up, and the engine works. But there's too much friction from the beginning; I would not hand it to a beginner.

My coding agents, on the other hand, were happy with the tool: they understood it fast and built the grammar and the demos in no time.

That is exactly the project's own thesis:

"An extensible parsing engine, and a compile target for agents."

So... Vercel doesn't have built-in email?

PabloDevRel — Thu, 20 Aug 2026 12:51:32 +0000

Old-school hosting always came with email. GoDaddy, Hostinger, IONOS.
You picked a plan, you got a mailbox, done.

But Vercel doesn't. And honestly? That's a good thing. Vercel is great at what it does, deploying and hosting web apps. But email is a completely different beast.

If you have a side project on a custom domain and want a professional address like hello@yourdomain.com, you need an external mail provider.

One I found that's worth a look: Amelu. It's not super well-known yet, but they have a solid free tier: 3 mailboxes, full IMAP/SMTP support and they're hosted in Europe, which is a plus if data residency matters to you.

Here's how I set it up for my side project moviekombat.app.

The DNS problem

Right now, DNS routes all moviekombat.app traffic to Vercel. That's fine for the website, but I need email to go somewhere else. The goal: tell DNS that any mail sent to @moviekombat.app should be handled by Amelu, not Vercel.

Step 1. Create an Amelu account

Go to app.amelu.org
Click "Login with Ordnary account"
Log in with your email. A first-time login automatically creates your account and organization.
You land on the Email Domains page, empty and ready

Step 2. Add your domain

Click Email Domains → New domain
Fill in:
- Domain name: your domain (just yourdomain.com, no www)
- DNS Nameservers: "Use external nameservers" (this doesn't change anything, you keep your existing DNS provider)
- Default Email Addresses: leave checked. This creates admin, postmaster, and abuse (required by email standards)
Click "Add Email Domain"

Amelu creates the domain and three default mailboxes. Copy the passwords, they're shown only once.

Step 3. Download and fix the DNS Zone file

Open DNS Configuration > DNS Config in Amelu. Those are the records you need to add to your domain's DNS provider. In our case, Vercel.

We could add each record one by one in Vercel's DNS Records form. Tedious for 19 records. So let's use the zone file import feature instead:

Download the zone file from Amelu (BIND format .zone file)
If you upload the zone file as-is in Vercel, you'll get an error.

[!CAUTION]
Error: No fully qualified domain name found in $ORIGIN directive or SOA record.

To fix that, open the zone file with a text editor and add this line at the top (after the comment header) $ORIGIN moviekombat.app. This is how my zone file looks:

; Amelu DNS zone file for moviekombat.app
; Generated 2026-08-15T12:02:27Z
; Import this into your DNS provider (e.g. Cloudflare > DNS > Import and Export).

$ORIGIN moviekombat.app.

@ IN SOA marduk.mx.amelu.org. postmaster.moviekombat.app. (
  ...

Step 4. Import the zone file into Vercel

In Vercel, go to Domains → select moviekombat.app → DNS Records
Click the Upload Zone File button and upload the zone file

Done! All records appear in your DNS table.

Step 5. Verify DNS in Amelu

Go back to Amelu DNS Configuration → DNS Config and click Recheck DNS. Most records come back Matched immediately.

A few things to know:

SRV records show "Not verified": that's normal. Amelu only live-checks MX, TXT, and CNAME. SRV/CAA are unchecked by design and don't block activation.
RSA DKIM might show mismatch: if Vercel's importer mangled the multi-line TXT record (split it with a literal " " in the middle), delete that record in Vercel and re-add it as a single concatenated string.

Once all required records match, the domain goes active.

Step 6. Configure your mail client

This is where Amelu's admin panel stops and your mail client starts. Amelu isn't a mail client, it manages domains and mailboxes. To read and send mail, you need IMAP/SMTP settings.

Find them in Amelu: Mailboxes → Usage Instructions:

IMAP: marduk.mx.amelu.org, port 993, SSL/TLS
SMTP: marduk.mx.amelu.org, port 465, SSL/TLS
Username: full email address (admin@yourdomain.com)
Password: the mailbox password

What else is out there?

Before landing on Amelu, I looked at the usual suspects:

Cloudflare Email Routing: free, but it only forwards. You can receive mail, but you can't send from your domain. No IMAP/SMTP, no inbox. It looks easy until you realize it's a one-way street.
Zoho Mail: has a free tier, but blocks IMAP on the free plan. You're stuck using their web client or mobile app. If you want to use Outlook or Thunderbird, you're paying.
Migadu: closest competitor. Full IMAP/SMTP, unlimited mailboxes, flat pricing. But they killed their free tier in 2020, and the cheapest plan is $19/year.

Amelu isn't perfect. There's no web client, so you read and send mail through Outlook, Thunderbird, or your phone's mail app. Auto-configuration doesn't work yet, so you'll set up the client manually the first time. But the free tier is real, the protocols are open, and the setup takes about 5 minutes.

For a Vercel side project where you just need hello@yourdomain.com to work, it gets the job done.

So... Vercel doesn't have built-in email?

PabloDevRel — Thu, 20 Aug 2026 10:03:46 +0000

Vercel is great for deploying web apps. But there's one thing it doesn't do: email.

If you have a side project on a custom domain and want a professional address like hello@yourdomain.com, you need an external mail provider. I went through the options. Cloudflare only forwards (no sending), Zoho locks you into their web client, and Migadu killed their free tier.

Then I found Amelu. Free tier, 3 mailboxes, full IMAP/SMTP support, hosted in Europe. Here's how I set it up for moviekombat.app.

The DNS problem

Step 1. Create an Amelu account

Go to app.amelu.org
Click "Login with Ordnary account"
Log in with your email. A first-time login automatically creates your account and organization.
You land on the Email Domains page, empty and ready

Step 2. Add your domain

Click Email Domains → New domain
Fill in:
- Domain name: your domain (just yourdomain.com, no www)
- DNS Nameservers: "Use external nameservers" (this doesn't change anything, you keep your existing DNS provider)
- Default Email Addresses: leave checked. This creates admin, postmaster, and abuse (required by email standards)
Click "Add Email Domain"

Amelu creates the domain and three default mailboxes. Copy the passwords, they're shown only once.

Step 3. Download and fix the DNS Zone file

Open DNS Configuration > DNS Config in Amelu. Those are the records you need to add to your domain's DNS provider. In our case, Vercel.

We could add each record one by one in Vercel's DNS Records form. Tedious for 19 records. So let's use the zone file import feature instead:

Download the zone file from Amelu (BIND format .zone file)
If you upload the zone file as-is in Vercel, you'll get an error.

[!CAUTION]
Error: No fully qualified domain name found in $ORIGIN directive or SOA record.

To fix that, open the zone file with a text editor and add this line at the top (after the comment header) $ORIGIN moviekombat.app. This is how my zone file looks:

; Amelu DNS zone file for moviekombat.app
; Generated 2026-08-15T12:02:27Z
; Import this into your DNS provider (e.g. Cloudflare > DNS > Import and Export).

$ORIGIN moviekombat.app.

@ IN SOA marduk.mx.amelu.org. postmaster.moviekombat.app. (
  ...

Step 4. Import the zone file into Vercel

In Vercel, go to Domains → select moviekombat.app → DNS Records
Click the Upload Zone File button and upload the zone file

Done! All records appear in your DNS table.

Step 5. Verify DNS in Amelu

Go back to Amelu DNS Configuration → DNS Config and click Recheck DNS. Most records come back Matched immediately.

A few things to know:

SRV records show "Not verified": that's normal. Amelu only live-checks MX, TXT, and CNAME. SRV/CAA are unchecked by design and don't block activation.
RSA DKIM might show mismatch: if Vercel's importer mangled the multi-line TXT record (split it with a literal " " in the middle), delete that record in Vercel and re-add it as a single concatenated string.

Once all required records match, the domain goes active.

Step 6. Configure your mail client

This is where Amelu's admin panel stops and your mail client starts. Amelu isn't a mail client, it manages domains and mailboxes. To read and send mail, you need IMAP/SMTP settings.

Find them in Amelu: Mailboxes → Usage Instructions:

IMAP: marduk.mx.amelu.org, port 993, SSL/TLS
SMTP: marduk.mx.amelu.org, port 465, SSL/TLS
Username: full email address (admin@yourdomain.com)
Password: the mailbox password

What else is out there?

Before landing on Amelu, I looked at the usual suspects:

Cloudflare Email Routing: free, but it only forwards. You can receive mail, but you can't send from your domain. No IMAP/SMTP, no inbox. It looks easy until you realize it's a one-way street.
Zoho Mail: has a free tier, but blocks IMAP on the free plan. You're stuck using their web client or mobile app. If you want to use Outlook or Thunderbird, you're paying.
Migadu: closest competitor. Full IMAP/SMTP, unlimited mailboxes, flat pricing. But they killed their free tier in 2020, and the cheapest plan is $19/year.

For a Vercel side project where you just need hello@yourdomain.com to work, it gets the job done.

DEV Community: PabloDevRel

Tabnas: How to define a grammar

What is a Grammar?

The Abaqus .inp files

Abaqus .inp parser

Tabnas

What you can do with your Tabnas Grammar?

1. Validate an .inp file

✅ Valid cube.inp file

❌ Invalid truncated.inp

2. Inspect your file keywords

3. Turn the file into JSON

Why a grammar?

Lightweight and reliable source of truth

Error proof

Adding a keyword does not touch the grammar

Are there other tools to generate a grammar?

Ohm vs Tabnas

Maturity

The webpage

The syntax

Conclusion

So... Vercel doesn't have built-in email?

The DNS problem

Step 1. Create an Amelu account

Step 2. Add your domain

Step 3. Download and fix the DNS Zone file

Step 4. Import the zone file into Vercel

Step 5. Verify DNS in Amelu

Step 6. Configure your mail client

What else is out there?

So... Vercel doesn't have built-in email?

The DNS problem

Step 1. Create an Amelu account

Step 2. Add your domain

Step 3. Download and fix the DNS Zone file

Step 4. Import the zone file into Vercel

Step 5. Verify DNS in Amelu

Step 6. Configure your mail client

What else is out there?

The Abaqus `.inp` files

1. Validate an `.inp` file

✅ Valid `cube.inp` file

❌ Invalid `truncated.inp`