Add Czech stemmer

README.md

@@ -6,6 +6,7 @@ This crate implements some stemmer algorithms found in the [snowball project](ht
 
 -   Arabic
 -   Armenian
+-   Czech
 -   Danish
 -   Dutch
 -   English

algorithms/czech.sbl

@@ -0,0 +1,255 @@
+/*
+ * Czech language stemmer
+ *
+ * Source obtained from https://snowballstem.org/algorithms/czech/stemmer.html,
+ * created by Ljiljana Dolamic & Jacques Savoy in 2009 (thank you :)
+ */
+
+routines (
+  RV R1
+  palatalise
+  mark_regions
+  do_possessive
+  do_case
+  do_comparative
+  do_diminutive
+  do_augmentative
+  do_derivational
+  do_deriv_single
+  do_aggressive
+)
+
+externals ( stem )
+
+integers ( pV p1 )
+
+groupings ( v )
+
+stringescapes {}
+
+stringdef a' '{U+00E1}'
+stringdef c^ '{U+010D}'
+stringdef d^ '{U+010F}'
+stringdef e' '{U+00E9}'
+stringdef e^ '{U+011B}'
+stringdef i' '{U+00ED}'
+stringdef n^ '{U+0148}'
+stringdef o' '{U+00F3}'
+stringdef r^ '{U+0159}'
+stringdef s^ '{U+0161}'
+stringdef t^ '{U+0165}'
+stringdef u' '{U+00FA}'
+stringdef u* '{U+016F}'
+stringdef y' '{U+00FD}'
+stringdef z^ '{U+017E}'
+
+define v 'aeiouy{a'}{e^}{e'}{i'}{o'}{u'}{u*}{y'}'
+
+define mark_regions as (
+
+    $pV = limit
+    $p1 = limit
+
+    do (
+        gopast non-v setmark pV
+        gopast non-v gopast v setmark p1
+    )
+)
+
+backwardmode (
+
+  define RV as $pV <= cursor
+  define R1 as $p1 <= cursor
+
+  define palatalise as (
+    [substring] RV among (
+      'ci' 'ce' '{c^}i' '{c^}'
+      (<- 'k')
+      'zi' 'ze' '{z^}i' '{z^}e'
+      (<- 'h')
+      '{c^}t{e^}' '{c^}ti' '{c^}t{e'}'
+      (<- 'ck')
+      '{s^}t{e^}' '{s^}ti' '{s^}t{e'}'
+      (<- 'sk')
+    )
+  )
+
+  define do_possessive as (
+    [substring] RV among (
+      'ov' '{u*}v'
+      (delete)
+      'in'
+      (
+        delete
+        try palatalise
+      )
+    )
+  )
+
+  define do_case as (
+    [substring] among (
+      'atech'
+      '{e^}tem' 'at{u*}m'
+      '{a'}ch' '{y'}ch' 'ov{e'}' '{y'}mi'
+      'ata' 'aty' 'ama' 'ami' 'ovi'
+      'at' '{a'}m' 'os' 'us' '{y'}m' 'mi' 'ou'
+      'u' 'y' '{u*}' 'a' 'o' '{a'}' '{e'}' '{y'}'
+      (delete)
+      'ech' 'ich' '{i'}ch'
+      '{e'}ho' '{e^}mi' '{e'}mu' '{e^}te' '{e^}ti' '{i'}ho' '{i'}mi'
+      'emi' 'iho' 'imu'
+      '{e'}m' '{i'}m' 'es'
+      'e' 'i' '{i'}' '{e^}'
+      (
+        delete
+        try palatalise
+      )
+      'em'
+      (
+        <- 'e'
+        try palatalise
+      )
+    )
+  )
+
+  define do_derivational as (
+    [substring] R1 among (
+      'obinec'
+      'ovisk' 'ovstv' 'ovi{s^}t' 'ovn{i'}k'
+      '{a'}sek' 'loun' 'nost' 'teln' 'ovec' 'ov{i'}k' 'ovtv' 'ovin' '{s^}tin'
+      '{a'}rn' 'och' 'ost' 'ovn' 'oun' 'out' 'ou{s^}' 'u{s^}k'
+      'kyn' '{c^}an' 'k{a'}{r^}' 'n{e'}{r^}' 'n{i'}k' 'ctv' 'stv'
+      '{a'}{c^}' 'a{c^}' '{a'}n' 'an' '{a'}{r^}' 'as'
+      'ob' 'ot' 'ov' 'o{n^}' 'ul' 'yn'
+      '{c^}k' '{c^}n' 'dl' 'nk' 'tv' 'tk' 'vk'
+      (delete)
+      'ion{a'}{r^}'
+      'inec' 'itel'
+      'i{a'}n' 'ist' 'isk' 'i{s^}k' 'itb'
+      'ic' 'in' 'it' 'iv'
+      (
+        <- 'i'
+        palatalise
+      )
+      'enic' 'ec' 'en'
+      (
+        <- 'e'
+        palatalise
+      )
+      '{e'}{r^}'
+      (
+        <- '{e'}'
+        palatalise
+      )
+      '{e^}n'
+      (
+        <- '{e^}'
+        palatalise
+      )
+      '{i'}rn'
+      '{i'}{r^}' '{i'}n'
+      (
+        <- '{i'}'
+        palatalise
+      )
+    )
+  )
+  define do_deriv_single as (
+    [substring] among (
+      'c' '{c^}' 'k' 'l' 'n' 't'
+      (delete)
+    )
+  )
+
+
+  define do_augmentative as (
+    [substring] among (
+      'ajzn' '{a'}k'
+      (delete)
+      'izn' 'isk'
+      (
+        <- 'i'
+        palatalise
+      )
+    )
+  )
+
+  define do_diminutive as (
+    [substring] among (
+      'ou{s^}ek' '{a'}{c^}ek' 'a{c^}ek' 'o{c^}ek' 'u{c^}ek'
+      'anek' 'onek' 'unek' '{a'}nek'
+      'e{c^}k' '{e'}{c^}k' 'i{c^}k' '{i'}{c^}k' 'enk' '{e'}nk' 'ink' '{i'}nk'
+      '{a'}{c^}k' 'a{c^}k' 'o{c^}k' 'u{c^}k' 'ank' 'onk' 'unk'
+      '{a'}tk' '{a'}nk' 'u{s^}k'
+      'k'
+      (delete)
+      'e{c^}ek' 'enek' 'ek'
+      (
+        <- 'e'
+        palatalise
+      )
+      '{e'}{c^}ek' '{e'}k'
+      (
+        <- '{e'}'
+        palatalise
+      )
+      'i{c^}ek' 'inek' 'ik'
+      (
+        <- 'i'
+        palatalise
+      )
+      '{i'}{c^}ek' '{i'}k'
+      (
+        <- '{i'}'
+        palatalise
+      )
+      '{a'}k'
+       (<- '{a'}')
+      'ak'
+       (<- 'a')
+      'ok'
+       (<- 'o')
+      'uk'
+       (<- 'u')
+    )
+  )
+
+  define do_comparative as (
+    [substring] among (
+      '{e^}j{s^}'
+      (
+        <- '{e^}'
+        palatalise
+      )
+      'ej{s^}'
+      (
+        <- 'e'
+        palatalise
+      )
+    )
+  )
+
+  define do_aggressive as (
+    do do_comparative
+    do do_diminutive
+    do do_augmentative
+    do_derivational or do_deriv_single
+  )
+)
+
+define stem as (
+  do mark_regions
+  backwards (
+    do_case
+    do_possessive
+    // light and aggressive are the same to this point
+    // comment next line for light stemmer
+    do_aggressive
+  )
+)
+
+// Ljiljana Dolamic and Jacques Savoy. 2009.
+// Indexing and stemming approaches for the Czech language.
+// Inf. Process. Manage. 45, 6 (November 2009), 714-720.
+// http://members.unine.ch/jacques.savoy/clef/CzechStemmerLight.txt
+// http://members.unine.ch/jacques.savoy/clef/CzechStemmerAgressive.txt

src/lib.rs

@@ -37,6 +37,7 @@ use snowball::algorithms;
 pub enum Algorithm {
     Arabic,
     Armenian,
+    Czech,
     Danish,
     Dutch,
     English,
@@ -67,6 +68,7 @@ impl Stemmer {
         match lang {
             Algorithm::Arabic => Stemmer { stemmer: algorithms::arabic::stem },
             Algorithm::Armenian => Stemmer { stemmer: algorithms::armenian::stem },
+            Algorithm::Czech => Stemmer { stemmer: algorithms::czech::stem },
             Algorithm::Danish => Stemmer { stemmer: algorithms::danish::stem },
             Algorithm::Dutch => Stemmer { stemmer: algorithms::dutch::stem },
             Algorithm::English => Stemmer { stemmer: algorithms::english::stem },