A formal grammar for Malayalam syllables

I wrote about formal grammar for Malayalam conjunct in last blog post. Continuing from there, let us discuss the syllable model.

A syllable is a unit of organization for a sequence of speech sounds. Each syllable can be considered as pronounciation units that constitutes a word pronounciation. For example, “മലയാളം” has മ, ല, യാ, ളം as 4 syllables. If you ask a native Malayalam speaker, “How many letters are in the word മലയാളം?” The answer would be 4 and it corresponds to syllable count. The ‘letter’ concept, known as ‘അക്ഷരം’ in Malayalam often refers to syllables.

Along with a verbal description of syllables in Malayalam we attempt to formalize a grammar using PEG – Parser Expression grammar. That grammar is then used for writing a parser to find the syllables in a given word. A web interface is also provided to try out the system.

Before starting with definition of syllable model, we need to define some terminology.

Definitions

  1. Vowel – Vowels of Malayalam -Any of the set: [അആഇഈഉഊഋഎഏഐഒഓഔഔഅം]
  2. VowelSign – Vowel signs. – Any of the set [ാിീുൃെേൊോൗൂൈ]
  3. Consonant – Consonants – Any of the set [കഖഗഘങചഛജഝഞടഠഡഢണതഥദധനപഫബഭമയരലവശഷസഹളഴറ]
  4. Virama – The sign ്.
  5. Visarga The sign ഃ
  6. Anuswara – The vowel sign of അം.ie ം. This share some properties of Chillu.
  7. Chillu – Pure consonants, without any vowels. Chillus are any of ൻ, ർ, ൽ, ൾ, ൺ, ൿ, ൔ, ൕ, ൖ. The last 4 chillus are rarely used or archaic. But we can consider them for our modeling. Due to historic encoding reasons, Chillus can also appear as base Consonant+Virama+ZWJ form. That means, ൻ = ന + ് + ZWJ. Chillus never appear in the begininning of word, but is not relevant for a syllable analyser.
  8. ZWNJ Zero Width Non Joiner.\u200C
  9. ZWJ Zero with Joiner \u200D
  10. Signs A term used to address various signs that modify a Consonant. Any of VowelSign, Virama, Anuswara, Visarga.
  11. Conjunct:Refer the formal definition of this we discussed in previous blog post. We defined it as A Consonant combined with another Conjunct or Consonant using Virama. Example: സ+ ് + ത => സ്ത , സ്ത + ് + ര = സ്ത്ര. ദ്ധ + ് ര = ദ്ധ്ര, ദ്ധ്ര + ് + യ = ദ്ധ്ര്യ. But we need an advanced version. That definition did not support DotReph (ൎ) which combines with a consonant or conjunct to form Conjunct. To support DotReph as well, we will redefine Conjunct as HalfConsonant Conjunct / Consonant
  12. DotReph The sign (ൎ). It combines with other consonants as in this example: ൎ + യ -> ൎയ in ഭാൎയ
  13. HalfConsonant: A Consonant followed by Virama Example: പ്, ര്, മ് etc. Or a DotReph

Syllable model

A syllable in Malayalam can be any of the following.

  1. An independent Vowel. Vowels are often found at the begininning of the word. Example: അമ്മ. But for the specific case of Syllables, we can relax this rule of being in the start of word and generally state that a vowel is syllable. Note that vowel appearing as vowel sign is not what we are considering here. Vowel signs has its own properties.
  2. A Chillu letter is a syllable.
  3. A Consonant without any Signs is a syllable. For example, in the word തറ, both ത and റ are Syllables.
  4. A Consonant or Conjunct with Signs is a syllable. Here the Signs can be repeated more than once, but not freely. This syllable has the following characteristics:
    1. Signs can be Virama only if it is the last items of a given word. For example. അത് has അ, ത് as syllables, but അത്ഭുതം has അ, ത്ഭു, തം as syllables.
    2. Signs can occur 2 times in folllowing cases:(a) First Sign is ു and Second is Virama This combination is also called Samvruthokaram. Example: തു് in അതു്. (b) First Sign is a VowelSign and Second is Anuswara. Examples: താം, തീം, തോം, തും etc.
  5. A ZWNJ marks a syllable boundary. A ZWNJ inserted between two blocks of text inserts a ligature as well as syllable boundary. For example: തമിഴ്‌നാട്, the ZWNJ inserted after ഴ് and before നാ prevents possible ഴ്ന Conjunct and hence also makes a point that the pronounciation should break at that point. It is a bit wierd to say a ZWNJ forms a syllable since it is just a seperator. But while analysing a series of letters from begininning to end, it is technically okey to consider ZWNJ as a syllable block.

Parser Expression Grammar

You can try this in a PEG evaluator and try various conjucts to see if they all getting parsed. Use https://pegjs.org/online, copy paste the above grammar try inputs like ‘ശാസ്ത്രവിഷയങ്ങൾ’.

Characteristics of the Grammar

There are a few important characteristics of this grammar.

It does certain validations against the signs. For example, it does not allow a VowelSign, virama or anuswara after a visarga. If that happens, the parser will fail to parse a word. It permits a virama after a VowelSign, but that is only for Samvruthokaram(vowel sign = ു ).

Among the signs, you can see Virama, but it is permitted only at the end of the word. For example: അത്. If virama comes in between a word, it has the nature of consonant combining.

The order of Signs is also enforced. For example, you cannot have a virama and then VowelSign ു even though the reverse order is permitted.

Above rules creates some strictness for the parser. At the same time, there are some relaxed rules too. There is no maximum limit on a possible conjuct.  A nonsense conjunct like ‘ക്ച്ട്ത്പ്ബ്ഭ്മ്ജ്ത്ക്’ will be accepted by parser. Malayalam has valid conjuncts upto 5 as far as I know(Example: ഗ്ദ്ധ്ര്യ ). Usually the longer conjuncts will have the ending consonants as യ, ര, ല, വ.

In informal Malayalam, vowel sign duplication is sometimes used to denote elongation. For example, വാടാാാ. Our parser won’t accept that.

Syllable boundaries

If you want to know syllable boundaries and don’t care about anything else, there is an easy way to find boundaries.

A syllable boundary is after:

  1. A vowel. Note that this not vowel sign. Example: അ|റ, ഇ|ര, ഉ|പ്പ്
  2. A vowel sign, if not followed by virama, anuswara or visarga. Example: ത്തി|ൽ, പു|ക,
  3. A consonant if followed by another consonant or chillu. Example: ത|റ, ഷ്ട|മി, ക|ൽ
  4. A chillu. Example: സ|ർ|പ്പം
  5. An Anuswara. Example: കു|ടും|ബം,
  6. A Visarga. Example: ദുഃ|ഖം
  7. A ZWNJ is syllable boundary.

Web interface

I prepared a web interface if you just want to try out the syllable analyser and dont want to play with PEG.

https://phon.smc.org.in/syllables/

Malayalam syllable analyser

Now that comes with a JS API too, just include the following file in your web application:

https://phon.smc.org.in/syllables/lib/malayalam-syllables.js

Then use the following method to split a word to syllables.

malayalamSyllableParser.parse(inputWord)

I prepared a codepen project to demonstrate this.

See the Pen Malayalam syllable analyser by Santhosh Thottingal (@santhoshtr) on CodePen.

Source code

https://github.com/santhoshtr/malayalam-syllable-analyser

Please report any issues or ideas to improve this model there. Thanks!

A formal grammar for Malayalam conjunct

In Malayalam a conjunct(കൂട്ടക്ഷരം) is formed by combining 2 or more consonants by Virama(ചന്ദ്രക്കല).  “ക്ക” is a conjunct with 2 consonants, formed by ക + ് + ക. സ്ത്ര is a conjuct with 3 consonants സ+ ് + ത +്+ ര. ന്ത്ര്യ  is a conjunct with 4 consonants – ന + ് + ത + ് + ര + ് + യ. Conjuncts with more than 4 consonant is rare. ഗ്ദ്ധ്ര്യ is formed by 5 consonants.

Can we define this formation in a formal grammar?

Let us try. For the simplicity, I am using Parser Expression Grammar formalism since we can quickly write a parser for that to test and evaluate.

Before that let us define the conjuct in plain English in a bit more concise and unambigous way.

Conjunct: A Consonant combined with another Conjunct or Consonant using Virama

We need to define Consonant and Virama also.

  • Virama:   ്.
  • Consonants – Any of the set [കഖഗഘങചഛജഝഞടഠഡഢണതഥദധനപഫബഭമയരലവശഷസഹളഴറ]

Writing this in PEG syntax


You can try this in a PEG evaluator and try various conjucts to see if they all getting parsed. Use https://pegjs.org/online, copy paste the above grammar try inputs like ന്ത്ര്യ.

Let us look at the definition again.

Conjunct = Consonant Virama (Conjunct / Consonant )

This is a tail recursion. Meaning, The Conjuct  get expanded towards the end of the expression. Can we rewrite this using a Left recursion? We can. see:

Conjunct = (Conjunct / Consonant ) Virama Consonant

This will have the same result of our previous expression. We can also rewrite our plain English definition as well accordingly:

Conjunct: A Conjunct or Consonant  combined with another Consonant using Virama

There is a problem with this new definition since it is Left recursion, depending up on the parser implementation, it can cause infinite recursion. The PEGjs parser which we used above for testing and evaluation does not support Left recursion since it is a top down parser(recursive descent parser). You can try modify the above pegjs grammar in the online evaluation tool, you will see the parser warns about ininite recursion.

But if the parser is capable of avoiding this issue, nothing stops you to write the grammar using Left recursion. LALR parsers such as GNU Bison can very well support left recursion. But big issue here is GNU Flex/Bison used for writing such grammars does not support Unicode!. You can make it working by doing some low level byte manipulation. I did not try.

One more thing: I wrote ( Conjunct / Consonant ) instead of (Consonant / Conjunct ). The order was chosen intentionally since the matches are done left to right. Since a Conjunct anyway start with a Consonant, the parsing will proceed with that path. We avoid it by using the Conjunct, Consonant order.