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// An implementation of "A Lightweight Stemmer for Hindi":
// http://www.kbcs.in/downloads/papers/StmmerHindi.pdf
externals ( stem )
stringescapes {}
// The transliteration scheme used for our stringdefs matches that used in the
// paper, as documented in the appendix. It appears to match the WX notation
// (https://en.wikipedia.org/wiki/WX_notation) except that WX apparently
// uses 'z' for Anunasika whereas the paper uses Mh.
//
// We discriminate dependent vowels by adding a leading "_" to their stringdef
// names (mnemonic: the _ signifies removing the implicit a from the preceding
// character).
// Vowels and sonorants:
stringdef a '{U+0905}'
stringdef A '{U+0906}'
stringdef i '{U+0907}'
stringdef I '{U+0908}'
stringdef u '{U+0909}'
stringdef U '{U+090A}'
stringdef q '{U+090B}'
stringdef e '{U+090F}'
stringdef E '{U+0910}'
stringdef o '{U+0913}'
stringdef O '{U+0914}'
// Vowel signs:
stringdef _A '{U+093E}'
stringdef _i '{U+093F}'
stringdef _I '{U+0940}'
stringdef _u '{U+0941}'
stringdef _U '{U+0942}'
stringdef _q '{U+0943}'
stringdef _e '{U+0947}'
stringdef _E '{U+0948}'
stringdef _o '{U+094B}'
stringdef _O '{U+094C}'
// Diacritics:
stringdef M '{U+0902}'
stringdef H '{U+0903}'
stringdef Mh '{U+0901}'
stringdef Z '{U+093C}' // Nukta
stringdef virama '{U+094D}'
// Velar consonants:
stringdef k '{U+0915}'
stringdef K '{U+0916}'
stringdef g '{U+0917}'
stringdef G '{U+0918}'
stringdef f '{U+0919}'
// Palatal consonants:
stringdef c '{U+091A}'
stringdef C '{U+091B}'
stringdef j '{U+091C}'
stringdef J '{U+091D}'
stringdef F '{U+091E}'
// Retroflex consonants:
stringdef t '{U+091F}'
stringdef T '{U+0920}'
stringdef d '{U+0921}'
stringdef D '{U+0922}'
stringdef N '{U+0923}'
// Dental consonants:
stringdef w '{U+0924}'
stringdef W '{U+0925}'
stringdef x '{U+0926}'
stringdef X '{U+0927}'
stringdef n '{U+0928}'
// Labial consonants:
stringdef p '{U+092A}'
stringdef P '{U+092B}'
stringdef b '{U+092C}'
stringdef B '{U+092D}'
stringdef m '{U+092E}'
// Semi-vowels:
stringdef y '{U+092F}'
stringdef r '{U+0930}'
stringdef l '{U+0932}'
stringdef v '{U+0935}'
// Fricatives:
stringdef S '{U+0936}'
stringdef R '{U+0937}'
stringdef s '{U+0938}'
stringdef h '{U+0939}'
stringdef lY '{U+0933}'
// Precomposed characters - letters + nukta:
stringdef nZ '{U+0929}' // ≡ {n}{Z}
stringdef rZ '{U+0931}' // ≡ {r}{Z}
stringdef lYZ '{U+0934}' // ≡ {lY}{Z}
stringdef kZ '{U+0958}' // ≡ {k}{Z}
stringdef KZ '{U+0959}' // ≡ {K}{Z}
stringdef gZ '{U+095A}' // ≡ {g}{Z}
stringdef jZ '{U+095B}' // ≡ {j}{Z}
stringdef dZ '{U+095C}' // ≡ {d}{Z}
stringdef DZ '{U+095D}' // ≡ {D}{Z}
stringdef PZ '{U+095E}' // ≡ {P}{Z}
stringdef yZ '{U+095F}' // ≡ {y}{Z}
groupings ( consonant )
routines ( CONSONANT )
define consonant '{k}{K}{g}{G}{f}' +
'{c}{C}{j}{J}{F}' +
'{t}{T}{d}{D}{N}' +
'{w}{W}{x}{X}{n}' +
'{p}{P}{b}{B}{m}' +
'{y}{r}{l}{v}' +
'{S}{R}{s}{h}' +
'{lY}' +
'{Z}' + // Nukta
// Precomposed characters - letter and nukta:
'{nZ}{rZ}{lYZ}{kZ}{KZ}{gZ}{jZ}{dZ}{DZ}{PZ}{yZ}'
backwardmode ( define CONSONANT as ( consonant ) )
define stem as (
// We assume in this implementation that the whole word doesn't count
// as a valid suffix to remove, so we remove the longest suffix from
// the list which leaves at least one character. This change affects
// 47 words out of the 65,140 in the sample vocabulary from Hindi
// wikipedia.
//
// The trick here is we use `next` in forward mode to advance the cursor
// to the second character, then `backwards` swaps the cursor and limit.
next
backwards (
[substring] among (
// The list below is derived from figure 3 in the paper.
//
// We perform the stemming on the Devanagari characters rather than
// transliterating to Latin, so we have adapted the list below to
// reflect this by converting suffixes back to Devanagari as
// follows:
//
// * within the suffixes, "a" after a consonant is dropped since
// consonants have an implicit "a".
//
// * within the suffixes, a vowel other than "a" after a consonant
// is a dependent vowel (vowel sign); a vowel (including "a")
// after a non-consonant is an independent vowel.
//
// * to allow the vowel at the start of each suffix being dependent
// or independent, we include each suffix twice. For the
// dependent version, a leading "a" is dropped and we check that
// the suffix is preceded by a consonant (which will have an
// implicit "a").
//
// * we add '{a}', which is needed for the example given right at
// the end of section 5 to work (conflating BarawIya and
// BarawIyawA), and which 3.1 a.v strongly suggests should be in
// the list:
//
// Thus, the following suffix deletions (longest possible
// match) are required to reduce inflected forms of masculine
// nouns to a common stem:
// a A i [...]
//
// Adding '{a}' only affect 2 words out of the 65,140 in the
// sample vocabulary.
//
// * The transliterations of our stems would end with "a" when our
// stems end in a consonant, so we also include {virama} in the
// list of suffixes to remove (this affects 222 words from the
// sample vocabulary).
//
// We've also assumed that Mh in the suffix list always means {Mh}
// and never {M}{h}{virama}. Only one of the 65,140 words in the
// sample vocabulary stems differently due to this (and that word
// seems to be a typo).
'{virama}'
'{a}'
'{A}'
'{i}'
'{I}'
'{u}'
'{U}'
'{e}'
'{o}'
'{e}{M}'
'{o}{M}'
'{A}{M}'
'{u}{A}{M}'
'{u}{e}{M}'
'{u}{o}{M}'
'{A}{e}{M}'
'{A}{o}{M}'
'{i}{y}{_A}{M}'
'{i}{y}{_o}{M}'
'{A}{i}{y}{_A}{M}'
'{A}{i}{y}{_o}{M}'
'{A}{Mh}'
'{i}{y}{_A}{Mh}'
'{A}{i}{y}{_A}{Mh}'
'{a}{w}{_A}{e}{M}'
'{a}{w}{_A}{o}{M}'
'{a}{n}{_A}{e}{M}'
'{a}{n}{_A}{o}{M}'
'{a}{w}{_A}'
'{a}{w}{_I}'
'{I}{M}'
'{a}{w}{_I}{M}'
'{a}{w}{_e}'
'{A}{w}{_A}'
'{A}{w}{_I}'
'{A}{w}{_I}{M}'
'{A}{w}{_e}'
'{a}{n}{_A}'
'{a}{n}{_I}'
'{a}{n}{_e}'
'{A}{n}{_A}'
'{A}{n}{_e}'
'{U}{M}{g}{_A}'
'{U}{M}{g}{_I}'
'{A}{U}{M}{g}{_A}'
'{A}{U}{M}{g}{_I}'
'{e}{M}{g}{_e}'
'{e}{M}{g}{_I}'
'{A}{e}{M}{g}{_e}'
'{A}{e}{M}{g}{_I}'
'{o}{g}{_e}'
'{o}{g}{_I}'
'{A}{o}{g}{_e}'
'{A}{o}{g}{_I}'
'{e}{g}{_A}'
'{e}{g}{_I}'
'{A}{e}{g}{_A}'
'{A}{e}{g}{_I}'
'{A}{y}{_A}'
'{A}{e}'
'{A}{I}'
'{A}{I}{M}'
'{i}{e}'
'{A}{o}'
'{A}{i}{e}'
'{a}{k}{r}'
'{A}{k}{r}'
'{_A}'
'{_i}'
'{_I}'
'{_u}'
'{_U}'
'{_e}'
'{_o}'
'{_e}{M}'
'{_o}{M}'
'{_A}{M}'
'{_u}{A}{M}'
'{_u}{e}{M}'
'{_u}{o}{M}'
'{_A}{e}{M}'
'{_A}{o}{M}'
'{_i}{y}{_A}{M}'
'{_i}{y}{_o}{M}'
'{_A}{i}{y}{_A}{M}'
'{_A}{i}{y}{_o}{M}'
'{_A}{Mh}'
'{_i}{y}{_A}{Mh}'
'{_A}{i}{y}{_A}{Mh}'
'{_I}{M}'
'{_A}{w}{_A}'
'{_A}{w}{_I}'
'{_A}{w}{_I}{M}'
'{_A}{w}{_e}'
'{_A}{n}{_A}'
'{_A}{n}{_e}'
'{_U}{M}{g}{_A}'
'{_U}{M}{g}{_I}'
'{_A}{U}{M}{g}{_A}'
'{_A}{U}{M}{g}{_I}'
'{_e}{M}{g}{_e}'
'{_e}{M}{g}{_I}'
'{_A}{e}{M}{g}{_e}'
'{_A}{e}{M}{g}{_I}'
'{_o}{g}{_e}'
'{_o}{g}{_I}'
'{_A}{o}{g}{_e}'
'{_A}{o}{g}{_I}'
'{_e}{g}{_A}'
'{_e}{g}{_I}'
'{_A}{e}{g}{_A}'
'{_A}{e}{g}{_I}'
'{_A}{y}{_A}'
'{_A}{e}'
'{_A}{I}'
'{_A}{I}{M}'
'{_i}{e}'
'{_A}{o}'
'{_A}{i}{e}'
'{_A}{k}{r}'
/* Suffixes with a leading implicit a: */
'{w}{_A}{e}{M}' CONSONANT
'{w}{_A}{o}{M}' CONSONANT
'{n}{_A}{e}{M}' CONSONANT
'{n}{_A}{o}{M}' CONSONANT
'{w}{_A}' CONSONANT
'{w}{_I}' CONSONANT
'{w}{_I}{M}' CONSONANT
'{w}{_e}' CONSONANT
'{n}{_A}' CONSONANT
'{n}{_I}' CONSONANT
'{n}{_e}' CONSONANT
'{k}{r}' CONSONANT
)
delete
)
)
|
