// Alias: ta

/*
* Affix stripping stemming algorithm for Tamil
* By Damodharan Rajalingam
*/

stringescapes {}

/* Aytham */
stringdef aytham   '{U+0B83}'

/* Uyir - independent vowels */
stringdef a        '{U+0B85}'
stringdef aa       '{U+0B86}'
stringdef i        '{U+0B87}'
stringdef ii       '{U+0B88}'
stringdef u        '{U+0B89}'
stringdef uu       '{U+0B8A}'
stringdef e        '{U+0B8E}'
stringdef ee       '{U+0B8F}'
stringdef ai       '{U+0B90}'
stringdef o        '{U+0B92}'
stringdef oo       '{U+0B93}'
stringdef au       '{U+0B94}'

/* Consonants */
stringdef ka       '{U+0B95}'
stringdef nga      '{U+0B99}'
stringdef ca       '{U+0B9A}'
stringdef ja       '{U+0B9C}'
stringdef nya      '{U+0B9E}'
stringdef tta      '{U+0B9F}'
stringdef nna      '{U+0BA3}'
stringdef ta       '{U+0BA4}'
stringdef tha      '{U+0BA4}'
stringdef na       '{U+0BA8}'
stringdef nnna     '{U+0BA9}'
stringdef pa       '{U+0BAA}'
stringdef ma       '{U+0BAE}'
stringdef ya       '{U+0BAF}'
stringdef ra       '{U+0BB0}'
stringdef rra      '{U+0BB1}'
stringdef la       '{U+0BB2}'
stringdef lla      '{U+0BB3}'
stringdef llla     '{U+0BB4}'
stringdef zha      '{U+0BB4}'
stringdef va       '{U+0BB5}'

/* Vatamozi - borrowed */
stringdef sha      '{U+0BB6}'
stringdef ssa      '{U+0BB7}'
stringdef sa       '{U+0BB8}'
stringdef ha       '{U+0BB9}'


/* Dependent vowel signs (kombu etc.) */
stringdef vs_aa    '{U+0BBE}'
stringdef vs_i     '{U+0BBF}'
stringdef vs_ii    '{U+0BC0}'
stringdef vs_u     '{U+0BC1}'
stringdef vs_uu    '{U+0BC2}'
stringdef vs_e     '{U+0BC6}'
stringdef vs_ee    '{U+0BC7}'
stringdef vs_ai    '{U+0BC8}'
stringdef vs_o     '{U+0BCA}'
stringdef vs_oo    '{U+0BCB}'
stringdef vs_au    '{U+0BCC}'

/* Pulli */
stringdef pulli    '{U+0BCD}'

/* AU length markk */
stringdef au_lmark '{U+0BD7}'


routines (
 remove_plural_suffix
 remove_question_suffixes
 remove_question_prefixes
 remove_pronoun_prefixes
 remove_command_suffixes
 remove_um
 remove_vetrumai_urupukal
 fix_va_start
 fix_ending
 fix_endings
 remove_tense_suffix
 remove_tense_suffixes
 remove_common_word_endings
 has_min_length
)

externals ( stem )

booleans (
 found_a_match
 found_vetrumai_urupu
)

define has_min_length as (
 $(len > 4)
)

define fix_va_start as (
 (try '{va}{vs_oo}' and [ '{va}{vs_oo}' ] <- '{oo}' ) or
 (try '{va}{vs_o}' and [ '{va}{vs_o}' ] <- '{o}' ) or
 (try '{va}{vs_u}' and [ '{va}{vs_u}' ] <- '{u}' ) or
 (try '{va}{vs_uu}' and [ '{va}{vs_uu}' ] <- '{uu}' )
)

define fix_endings as (
 do repeat fix_ending
)

define remove_question_prefixes as (
 [ ('{e}' ) among('{ka}' '{ca}' '{tha}' '{va}' '{na}' '{pa}' '{ma}' '{ya}' '{nga}' '{nya}') '{pulli}' ] delete
 do fix_va_start
)

// Gives signal t if an ending was fixed, signal f otherwise.
define fix_ending as (
 $(len > 3)
 backwards (
  ( [among('{na}{pulli}' '{na}{pulli}{ta}' '{na}{pulli}{ta}{pulli}') ] delete )
  or
  ( ['{ya}{pulli}' test among('{vs_ai}' '{vs_i}' '{vs_ii}') ] delete )
  or
  ( [ '{tta}{pulli}{pa}{pulli}' or '{tta}{pulli}{ka}{pulli}' ] <- '{lla}{pulli}' )
  or
  ( [ '{nnna}{pulli}{rra}{pulli}' ] <- '{la}{pulli}' )
  or
//		( [ '{rra}{pulli}{ka}{pulli}'  or '{nnna}{pulli}{nnna}{pulli}' ] <- '{la}{pulli}'  )
  ( [ '{rra}{pulli}{ka}{pulli}' ] <- '{la}{pulli}' )
  or
  ( [ '{tta}{pulli}{tta}{pulli}' ] <- '{tta}{vs_u}' )
  or
  ( found_vetrumai_urupu [ '{ta}{pulli}{ta}{pulli}' (test not '{vs_ai}') ] <- '{ma}{pulli}' ] )
  or
  ( [ '{vs_u}{ka}{pulli}' or '{vs_u}{ka}{pulli}{ka}{pulli}' ] <- '{pulli}' )
  or
  ( [ '{pulli}' among('{ka}' '{ca}' '{tta}' '{tha}' '{pa}' '{rra}') '{pulli}' among('{ka}' '{ca}' '{tta}' '{tha}' '{pa}' '{rra}') ] delete )
  or
  ( [ '{vs_u}{ka}{pulli}' ] <- '{pulli}' )
  or
  ( [ '{pulli}' among('{ka}' '{ca}' '{tta}' '{tha}' '{pa}' '{rra}') ] delete )
  or
  ( [ '{pulli}' (among('{ya}' '{ra}' '{la}' '{va}' '{zha}' '{lla}') or among('{nga}' '{nya}' '{nna}' '{na}' '{ma}' '{nnna}')) '{pulli}' ] <- '{pulli}' )
  or
  ( [ among('{va}' '{ya}' '{va}{pulli}') ] delete )
  or
  ( [ '{nnna}{vs_u}' (test not among('{vs_aa}' '{vs_i}' '{vs_ii}' '{vs_e}' '{vs_ee}' '{vs_u}' '{vs_uu}' '{vs_ai}')) ] delete )
  or
  ( [ '{nga}{pulli}' (test not '{vs_ai}')] <- '{ma}{pulli}' )
  or
  ( [ '{nga}{pulli}' ] delete )
  or
  ( [ '{pulli}' (test (among('{vs_aa}' '{vs_i}' '{vs_ii}' '{vs_e}' '{vs_ee}' '{vs_u}' '{vs_uu}' '{vs_ai}') or '{pulli}')) ] delete )
  )
)

define remove_pronoun_prefixes as (
 unset found_a_match
 [ among('{a}' '{i}' '{u}') among('{ka}' '{ca}' '{tha}' '{va}' '{na}' '{pa}' '{ma}' '{ya}' '{nga}' '{nya}') '{pulli}' ] delete
 (set found_a_match)
 do fix_va_start
)

define remove_plural_suffix as (
 unset found_a_match
 backwards (
  ( [ '{vs_u}{nga}{pulli}{ka}{lla}{pulli}' (test not among('{ka}' '{ca}' '{tta}' '{tha}' '{pa}' '{rra}')) ] <- '{pulli}' ) or
  ( [ '{rra}{pulli}{ka}{lla}{pulli}' ] <- '{la}{pulli}' ) or
  ( [ '{tta}{pulli}{ka}{lla}{pulli}' ] <- '{lla}{pulli}' ) or
  ( [ '{ka}{lla}{pulli}' ] delete )
  (set found_a_match)
 )
)

define remove_question_suffixes as (
 has_min_length
 unset found_a_match
 backwards (
  do (
   [ among('{vs_oo}' '{vs_ee}' '{vs_aa}') ] <- '{pulli}'
   (set found_a_match)
  )
 )
 do fix_endings
)

define remove_command_suffixes as (
 has_min_length
 unset found_a_match
 backwards (
  [ among('{pa}{vs_i}' '{va}{vs_i}') ] delete
  (set found_a_match)
 )
)

define remove_um as (
 unset found_a_match
 has_min_length
 backwards ( [ '{vs_u}{ma}{pulli}' ] <- '{pulli}'
    (set found_a_match)
    )
 do fix_ending
)

define remove_common_word_endings as (
 // These are not suffixes actually but are
 // some words that are attached to other words
 // but can be removed for stemming
 unset found_a_match
 has_min_length
 backwards (
  test ( [ '{vs_u}{tta}{nnna}{pulli}' or
     '{vs_i}{la}{pulli}{la}{vs_ai}' or
     '{vs_i}{tta}{ma}{pulli}' or
     '{vs_i}{nnna}{pulli}{rra}{vs_i}' or
     '{vs_aa}{ka}{vs_i}' or
     '{vs_aa}{ka}{vs_i}{ya}' or
     '{vs_e}{nnna}{pulli}{rra}{vs_u}' or
     '{vs_u}{lla}{pulli}{lla}' or
     '{vs_u}{tta}{vs_ai}{ya}' or
     '{vs_u}{tta}{vs_ai}' or
     '{vs_e}{nnna}{vs_u}{ma}{pulli}' or
     ('{la}{pulli}{la}' test (not among('{vs_aa}' '{vs_i}' '{vs_ii}' '{vs_e}' '{vs_ee}' '{vs_u}' '{vs_uu}' '{vs_ai}'))) or
     '{vs_e}{nnna}' or
     '{vs_aa}{ka}{vs_i}' ] <- '{pulli}'
     (set found_a_match)
     )
  or
  test ( [ among('{pa}{tta}{vs_u}'
     '{pa}{tta}{pulli}{tta}'
     '{pa}{tta}{pulli}{tta}{vs_u}'
     '{pa}{tta}{pulli}{tta}{ta}{vs_u}'
     '{pa}{tta}{pulli}{tta}{nna}'
     '{ka}{vs_u}{ra}{vs_i}{ya}'
     '{pa}{rra}{pulli}{rra}{vs_i}'
     '{va}{vs_i}{tta}{vs_u}'
     '{va}{vs_i}{tta}{pulli}{tta}{vs_u}'
     '{pa}{tta}{vs_i}{ta}{vs_aa}{nnna}'
     '{pa}{tta}{vs_i}'
     '{ta}{vs_aa}{nnna}'
     '{vs_e}{la}{pulli}{la}{vs_aa}{ma}{pulli}')
    ] delete
    (set found_a_match)
    )
 )
 do fix_endings
)

define remove_vetrumai_urupukal as (
 unset found_a_match
 unset found_vetrumai_urupu
 has_min_length
 backwards (
  (
    test ( ['{nnna}{vs_ai}'] delete )
   or
    test ([ ( '{vs_i}{nnna}{vs_ai}' or
     '{vs_ai}' (test not among('{ka}' '{ca}' '{tta}' '{tha}' '{pa}' '{rra}'))) or
      ( '{vs_ai}' (test (among('{ka}' '{ca}' '{tta}' '{tha}' '{pa}' '{rra}') '{pulli}')))
    ] <- '{pulli}'
    )
   or
   test ( [
            '{vs_o}{tta}{vs_u}' or
            '{vs_oo}{tta}{vs_u}' or
            '{vs_i}{la}{pulli}' or
            '{vs_i}{rra}{pulli}' or
            ('{vs_i}{nnna}{pulli}' (test not '{ma}')) or
            '{vs_i}{nnna}{pulli}{rra}{vs_u}' or
            '{vs_i}{ra}{vs_u}{na}{pulli}{ta}{vs_u}' or
            '{va}{vs_i}{tta}' or
            ($(len >= 7) '{vs_i}{tta}{ma}{pulli}') or
            '{vs_aa}{la}{pulli}' or
            '{vs_u}{tta}{vs_ai}' or
            '{vs_aa}{ma}{la}{pulli}' or
            ('{la}{pulli}' (test not among('{vs_aa}' '{vs_i}' '{vs_ii}' '{vs_e}' '{vs_ee}' '{vs_u}' '{vs_uu}' '{vs_ai}'))) or
            '{vs_u}{lla}{pulli}'
           ] <- '{pulli}'
     )
   or
   test ( [
           '{ka}{nna}{pulli}' or
           '{ma}{vs_u}{nnna}{pulli}' or
           '{ma}{vs_ee}{la}{pulli}' or
           '{ma}{vs_ee}{rra}{pulli}' or
           '{ka}{vs_ii}{llla}{pulli}' or
           '{pa}{vs_i}{nnna}{pulli}' or
           ('{ta}{vs_u}' (test not among('{vs_aa}' '{vs_i}' '{vs_ii}' '{vs_e}' '{vs_ee}' '{vs_u}' '{vs_uu}' '{vs_ai}')))
          ] delete
      )
   or
   test ([ '{vs_ii}' ] <- '{vs_i}')
  )
  (set found_a_match)
  (set found_vetrumai_urupu)
  do ( [ '{vs_i}{nnna}{pulli}' ] <- '{pulli}' )
 )
 do fix_endings
)

define remove_tense_suffixes as (
 set found_a_match
 repeat ( found_a_match (do remove_tense_suffix) )
)

define remove_tense_suffix as (
 unset found_a_match
 has_min_length
 backwards (
  do (
   test ( [among(
           '{ka}{vs_o}{nna}{pulli}{tta}{vs_i}{ra}{pulli}'
           '{pa}{tta}{vs_u}'
           )] delete
     (set found_a_match)
     )
   or
   test ( [
            '{ma}{vs_aa}{ra}{pulli}' or
            '{ma}{vs_i}{nnna}{pulli}' or
            '{nnna}{nnna}{pulli}' or
            '{nnna}{vs_aa}{nnna}{pulli}' or
            '{nnna}{vs_aa}{lla}{pulli}' or
            '{nnna}{vs_aa}{ra}{pulli}' or
            ('{va}{nnna}{pulli}' test (not among('{a}' '{aa}' '{i}' '{ii}' '{u}' '{uu}' '{e}' '{ee}' '{ai}' '{o}' '{oo}' '{au}')) ) or
            '{nnna}{lla}{pulli}' or
            '{va}{lla}{pulli}' or
            '{nnna}{ra}{pulli}' or
            '{va}{ra}{pulli}' or
            '{nnna}' or '{pa}' or '{ka}' or '{ta}' or '{ya}' or
            '{pa}{nnna}{pulli}' or
            '{pa}{lla}{pulli}' or
            '{pa}{ra}{pulli}' or
            ('{ta}{vs_u}' (test not among('{vs_aa}' '{vs_i}' '{vs_ii}' '{vs_e}' '{vs_ee}' '{vs_u}' '{vs_uu}' '{vs_ai}'))) or
            '{vs_i}{rra}{pulli}{rra}{vs_u}' or
            '{pa}{ma}{pulli}' or
            '{nnna}{ma}{pulli}' or
            '{ta}{vs_u}{ma}{pulli}' or
            '{rra}{vs_u}{ma}{pulli}' or
            '{ka}{vs_u}{ma}{pulli}' or
            '{nnna}{vs_e}{nnna}{pulli}' or
            '{nnna}{vs_ai}' or
            '{va}{vs_ai}'
       ] delete
       (set found_a_match)
       )
   or
   test ( [
           ('{vs_aa}{nnna}{pulli}' test (not '{ca}')) or
           '{vs_aa}{lla}{pulli}' or
           '{vs_aa}{ra}{pulli}' or
           '{vs_ee}{nnna}{pulli}' or
           '{vs_aa}' or
           '{vs_aa}{ma}{pulli}' or
           '{vs_e}{ma}{pulli}' or
           '{vs_ee}{ma}{pulli}' or
           '{vs_oo}{ma}{pulli}' or
           '{ka}{vs_u}{ma}{pulli}' or
           '{ta}{vs_u}{ma}{pulli}' or
           '{tta}{vs_u}{ma}{pulli}' or
           '{rra}{vs_u}{ma}{pulli}' or
           '{vs_aa}{ya}{pulli}' or
           '{nnna}{vs_e}{nnna}{pulli}' or
           '{nnna}{vs_i}{ra}{pulli}' or
           '{vs_ii}{ra}{pulli}' or
           '{vs_ii}{ya}{ra}{pulli}'
          ] <- '{pulli}'
      (set found_a_match)
      )
   or
   test ( ([ '{ka}{vs_u}' or '{ta}{vs_u}' ) (test '{pulli}') ] delete
      (set found_a_match)
      )
  )
  do ([among(
              '{vs_aa}{na}{vs_i}{nnna}{pulli}{rra}'
              '{vs_aa}{na}{vs_i}{nnna}{pulli}{rra}{pulli}'
              '{ka}{vs_i}{nnna}{pulli}{rra}'
              '{ka}{vs_i}{nnna}{pulli}{rra}{pulli}'
              '{ka}{vs_i}{rra}'
              '{ka}{vs_i}{rra}{pulli}'
            )] delete
    (set found_a_match)
    )
 )
 do fix_endings
)

define stem as (
 unset found_vetrumai_urupu
 do fix_ending
 has_min_length
 do remove_question_prefixes
 do remove_pronoun_prefixes
 do remove_question_suffixes
 do remove_um
 do remove_common_word_endings
 do remove_vetrumai_urupukal
 do remove_plural_suffix
 do remove_command_suffixes
 do remove_tense_suffixes
)
