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(**************************************************************************)
(*                                                                        *)
(*                     The Sanskrit Heritage Platform                     *)
(*                                                                        *)
(*                              Gérard Huet                               *)
(*                                                                        *)
7
(* ©2018 Institut National de Recherche en Informatique et en Automatique *)
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(**************************************************************************)

(* Dispatcher: Sanskrit Engine in 53 phases automaton (plus 2 fake ones) *)

(* The Dispatch functor maps a transducer vector of 39 aums into     *)
(*  - a dispatch automaton implementing a regular description over   *)
(*    45 phases of lexical analysis                                  *)
(*  - an initial vector of initial resumptions                       *)
(*  - a final test for lexical acceptance                            *)
(*  - a consistency check of the output of the segmenting transducer *)

(* Dispatch, instantiated by Transducers, is used as parameter of the 
   Segment functor from Segmenter or Interface.   *)

open Auto.Auto; 
open Load_transducers; (* [transducer_vect Trans roots_morpho krids_morpho] *)
open Skt_morph;
open Morphology; (* [inflected inflected_map Verb_form morphology] *)
open Naming; (* [homo_undo look_up_homo unique_kridantas] *)  
open Phases.Phases; (* phase etc. *)

module Dispatch 
  (* To be instantiated by Transducers from Lexer or Interface *) 
  (Trans: sig value transducers : transducer_vect;   
              value roots_usage : Deco.deco string; end) 
  (Lem: sig value morpho : morphology; end) = struct  
open Trans; 
open Lem;

(* [ transducer : phase -> auto ] *)
value transducer = fun
  [ Nouv -> transducers.nouv (* vowel-initial noun *)
  | Nouc -> transducers.nouc (* consonant-initial noun *)
  | Noun2 -> transducers.noun2 (* idem in mode non gen *) 
  | Pron -> transducers.pron (* declined pronouns *) 
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  | Root -> transducers.root (* conjugated root forms *) 
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  | Vokv -> transducers.vokv (* vowel-initial vocative k.rdaantas *)  
  | Vokc -> transducers.vokc (* consonant-initial vocative k.rdaantas *)  
  | Inde -> transducers.inde (* indeclinables, particles  *) 
  | Absv -> transducers.absv (* vowel-initial absolutives in -tvaa *) 
  | Absc -> transducers.absc (* consonant-initial absolutives in -tvaa *) 
  | Abso -> transducers.abso (* absolutives in -ya *) 
  | Iic2 -> transducers.iic2 (* idem in mode non gen *) 
  | Iiif -> transducers.iifc (* fake iic of ifc stems *) 
  | Iiv  -> transducers.iiv  (* in initio verbi nominal stems, perpft *) 
  | Inv  -> transducers.inv  (* invocations *)   
  | Auxi -> transducers.auxi       (* k.r and bhuu finite forms *)
  | Auxik -> transducers.auxik     (* k.r and bhuu kridanta forms *) 
  | Auxiick -> transducers.auxiick (* k.r and bhuu kridanta bare forms *)
  | Peri -> transducers.peri (* periphrastic perfect *)
  | Lopa -> transducers.lopa (* e/o root forms *)
  | Lopak -> transducers.lopak (* e/o kridanta forms *)
  | Ifc  -> transducers.ifc  (* in fine composi forms *)
  | Ifc2 -> transducers.ifc2 (* idem in mode non gen *)
  | Pv   -> transducers.prev (* preverbs *) 
  | Pvkc -> transducers.pvc  (* preverbs starting with consonant *) 
  | Pvkv -> transducers.pvv  (* preverbs starting with vowel *) 
  | A | Ai   -> transducers.a    (* privative a *)
  | An | Ani -> transducers.an   (* privative an *)
  | Iicv -> transducers.iicv (* vowel-initial iic *)
  | Iicc -> transducers.iicc (* consonant-initial iic *)
  | Iikv -> transducers.iikv (* vowel-initial iic k.rdaanta *)
  | Iikc -> transducers.iikc (* consonant-initial iic k.rdaanta *)
  | Iivv -> transducers.iivv (* vowel-initial iiv (cvi) *)
  | Iivc -> transducers.iivc (* consonant-initial iiv (cvi) *)
  | Kriv -> transducers.kriv (* vowel-initial krid *)
  | Kric -> transducers.kric (* consonant-initial krid *) 
  | Vocv -> transducers.vocv (* vowel-initial vocatives *)
  | Vocc -> transducers.vocc (* consonant-initial vocatives *)
  | Iiy  -> transducers.iiy  (* iic avyayiibhava *)
  | Avy  -> transducers.avya (* ifc avyayiibhava *)
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  | Inftu -> transducers.inftu (* infinitives in -tu iic. Renou HLS 72 *)
  | Kama -> transducers.kama (* ifcs of kaama/manas: tyaktukaama dra.s.tumanas *)
  | Sfx  -> transducers.sfx  (* ifc taddhita suffixes *) 
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  | Isfx -> transducers.isfx (* iifc taddhita suffixes *)
  | Cache -> transducers.cache (* cached forms *)
  | Noun | Iic | Iik | Voca | Krid | Pvk | Vok
    -> raise (Control.Anomaly "composite phase")
  | Unknown -> raise (Control.Anomaly "transducer - Unknown")
  | _ -> raise (Control.Anomaly "no transducer for fake phase") 
  ]
; 
(* Tests whether a word starts with a phantom phoneme (precooked aa-prefixed
   finite or participial or infinitive or abs-ya root form *)
value phantomatic = fun
  [ [ c :: _ ] -> c<(-2)
  | _ -> False
  ]
(* Amuitic forms start wiih -2 = [-] which elides preceding -a or -aa from Pv *)
and amuitic= fun
  [ [ -2 :: _ ] -> True 
  | _ -> False
  ]
;
(* We recognize $S = (Subst + Pron + Verb + Inde + Voca)^+$\\
   with $Verb = (1 + Pv).Root + Pv.Abso + Iiv.Auxi$,\\
       $Subst = Noun + Iic.Ifc + Iic.Subst + Iiv.Auxik$,\\
       $Noun = Nounv + Nounc$ and
       $Iic = Iicv + Iicc$\\
NB. $Abso$ = absolutives in -ya, 
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    $Inde$ contains absolutives in -tvaa 
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    $Voca = Vocv + Vocc$ (vocatives),
    $Auxi$ = finite forms of bhuu and k.r.\\
The following is obtained from the above recursion equation by Brzozowski's 
derivatives like in Berry-Sethi's translator. *)

value cached = (* potentially cached lexicon acquisitions *)
  if Web.cache_active.val="t" then [ Cache ] else []
;
(* initial1, initial2: phases *)
value initial1 =
   (* All phases but Ifc, Abso, Auxi, Auxik, Auxiick, Lopa, Lopak, Sfx, Isfx. *)
   [ Inde; Iicv; Iicc; Nouv; Nouc; Pron; A; An; Root; Kriv; Kric; Iikv; Iikc
   ; Peri; Pv; Pvkv; Pvkc; Iiv; Iivv; Iivc; Iiy; Inv; Ai; Ani; Absv; Absc; Inftu
   ; Vocv; Vocc; Vokv; Vokc ] @ cached
and initial2 =  (* simplified segmenter with less phases, no generation *)
   [ Inde; Iic2; Noun2; Pron; Root; Pv; Iiv; Absv; Absc ] 
;
value initial full = if full then initial1 else initial2
;
(* dispatch1: Word.word -> phase -> phases *)
value dispatch1 w = fun (* w is the current input word *)
  [ Nouv | Nouc | Pron | Inde | Abso | Auxi | Auxik | Kama | Ifc 
  | Kriv | Kric | Absv | Absc | Avy | Lopak | Sfx | Root | Lopa ->
       if phantomatic w then [ Root; Kriv; Kric; Iikv; Iikc; Abso ] (* aa- pv *) 
       else initial1
  | A -> if phantomatic w then []
         else [ Iicc; Nouc; Iikc; Kric; Pvkc; Iivc; Vocc; Vokc ]
  | An -> if phantomatic w then [] 
          else [ Iicv; Nouv; Iikv; Kriv; Pvkv; Iivv; Vocv; Vokv
          ; A (* eg anak.sara *) ; An (* attested ? *) ]
  | Ai -> [ Absc ]
  | Ani -> [ Absv ]
    (* This assumes that privative prefixes cannot prefix Ifc forms 
       justified by \Pan{2,2,6} a-x only if x is a subanta. *)
  | Iicv | Iicc | Iikv | Iikc | Iiif | Auxiick -> (* Compounding *)
       [ Iicv; Iicc; Nouv; Nouc; A; An; Ifc; Iikv; Iikc; Kriv; Kric
       ; Pvkv; Pvkc; Iiif; Iivv; Iivc; Vocv; Vocc; Vokv; Vokc ] @ 
       [ Sfx; Isfx ] @ cached
  | Pv -> if phantomatic w then [] else 
          if amuitic w then [ Lopa ] else [ Root; Abso; Peri; Inftu ]
  | Pvkc | Pvkv -> if phantomatic w then [] else 
          if amuitic w then [ Lopak ] else [ Iikv; Iikc; Kriv; Kric; Vokv; Vokc ]
  | Iiv -> [ Auxi ] (* as bhuu and k.r finite forms *)
  | Iivv | Iivc -> [ Auxik; Auxiick ] (* bhuu and k.r kridanta forms *)
  | Iiy -> [ Avy ]
  | Isfx -> (* Compounding with taddhita *)
       [ Iicv; Iicc; Nouv; Nouc; A; An; Ifc; Iikv; Iikc; Kriv; Kric
       ; Pvkv; Pvkc; Iiif; Iivv; Iivc; Vocv; Vocc; Vokv; Vokc ] @ cached
  | Peri -> [ Auxi ] (* overgenerates, should be only perfect forms *)
  | Inftu -> [ Kama ] 
  | Vocc | Vocv | Vokv | Vokc | Cache -> [] 
      (* only chunk-final vocatives so no Iic overlap *) 
  | Inv -> [ Vocv; Vocc; Vokv; Vokc ] (* invocations before vocatives *) 
(* Privative prefixes A and An are not allowed to prefix Ifc like a-dhii *)
  | Noun | Iic | Iik | Voca | Krid | Noun2 | Iic2 | Ifc2 | Pvk | Vok
  | Unknown -> failwith "Dispatcher anomaly"
  | _ -> failwith "Dispatcher fake phase" 
  ]
and dispatch2 w = fun (* simplified segmenter *)
  [ Noun2 | Pron | Inde | Abso | Absv | Absc | Auxi | Ifc2 ->
       if phantomatic w then [ Root; Abso ]
       else initial2
  | Root | Lopa -> if phantomatic w then [] (* no consecutive verbs in chunk *)
                   else [ Inde; Iic2; Noun2; Pron ]
  | Iic2 -> if phantomatic w then []
            else [ Iic2; Noun2; Ifc2 ]  
  | Pv -> if phantomatic w then [] else  
          if amuitic w then [ Lopa ] else [ Root; Abso ]
  | Iiv -> [ Auxi ] 
  | _ -> failwith "Dispatcher anomaly"
  ]
;
(* dispatch: bool -> Word.word -> phase -> phases *)
value dispatch full = if full then dispatch1 else dispatch2
;
value terminal = (* Accepting phases *)
   [ Nouv; Nouc; Noun2
   ; Pron
   ; Root 
   ; Kriv 
   ; Kric 
   ; Inde
   ; Abso; Absv; Absc
   ; Ifc; Ifc2
   ; Auxi; Auxik
   ; Vocc; Vocv; Vokv; Vokc; Inv 
   ; Lopa; Lopak
   ; Avy; Kama
   ; Sfx
   ; Cache
   ]
;

(* accepting: phase -> bool *)
value accepting phase = List.mem phase terminal
;
(* Segmenter control *)
type input = Word.word (* input sentence represented as a word *)
and transition = (* Reflexive relation *)
    [ Euphony of rule (* [(w,rev u,v)] such that [u|v -> w] *)
    | Id                   (* identity or no sandhi *)
    ]
and segment = (phase * Word.word * transition)
and output = list segment
;
(* Now consistency check - we check that preverbs usage is consistent with
   root px declaration in lexicon *)

value assoc_word word deco =
   let infos = Deco.assoc word deco in
   if infos = [] then failwith ("Unknown form: " ^ Canon.decode word)
   else infos
;
value autonomous root = (* root form allowed without preverb *)
  let infos = assoc_word root roots_usage in
  match infos with 
    [ [ "" :: _ ] -> True 
    | _ -> False
    ]
and attested prev root = (* prev is attested preverb sequence for root *)
  let pvs = assoc_word root roots_usage in
  List.mem prev pvs (* NB attested here means lexicalized entry *)
;
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value gana_o = fun 
  [ None -> 0 (* arbitrary *)
  | Some g -> g (* only used for "tap" *)
  ] 
and voice_o v = fun
  [ None -> True
  | Some voice -> voice = v
  ]
;
(* pvs is a list of preverb words *)
(* upasarga closest to the root form *)
value main_preverb pvs = List2.last pvs 
;
value main_preverb_string pv = 
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  Canon.decode (main_preverb (assoc_word pv Web.preverbs_structure))
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;
value attested_verb (o_gana,o_voice) pv root = attested pv root && 
  let gana = gana_o o_gana in
  let upasarga = main_preverb_string (Encode.code_string pv) in 
  try let pada = Pada.voices_of_pv upasarga gana (Canon.decode root) in
      match pada with
      [ Pada.Ubha -> True
      | _ -> voice_o pada o_voice 
      ] 
  with [ Pada.Unattested -> False ]
;
(* Similarly for root forms used without preverb *)
value autonomous_root (o_gana,o_voice) root = autonomous root &&  
  let gana = gana_o o_gana in 
  try let pada = Pada.voices_of_pv "" (*i glitch i*) gana (Canon.decode root) in 
      match pada with
      [ Pada.Ubha -> True
      | _ -> voice_o pada o_voice 
      ] 
  with [ Pada.Unattested -> False ]
;
value pada_of_voice = fun
  [ Active -> Some Pada.Para
  | Middle -> Some Pada.Atma
  | _ -> None 
  ] 
;
exception Unvoiced
;
value extract_gana_pada = fun
  [ Verb_form (conj,paradigm) _ _ -> 
       let (o_gana,voice) = match paradigm with
           [ Presenta g _ -> (Some g,Active)
           | Presentm g _ -> (Some g,Middle)
           | Presentp _   -> (None,Passive)
           | Conjug _ v | Perfut v -> (None,v)
           ] in
       (conj,(o_gana,pada_of_voice voice))
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  | Ind_verb _ _ -> raise Unvoiced (* could be refined *)
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  | _ -> failwith "Unexpected root form" 
  ]
and extract_gana_pada_k krit =
    let (o_gana,voice) = match krit with
       [ Ppp | Pprp | Pfutp _ -> (None,Passive)
       | Pppa | Ppfta | Pfuta -> (None,Active)
       | Ppftm | Pfutm -> (None,Middle)
       | Ppra g -> (Some g,Active)
       | Pprm g -> (Some g,Middle)
       | _ -> raise Unvoiced (* could be refined *)
       ] in
    (o_gana,pada_of_voice voice)
;
value fail_inconsistency form =
  raise (Control.Anomaly ("Unknown root form: " ^ Canon.decode form))
;
value valid_morph_pv pv root (morph : Morphology.inflexion_tag) = try
  let (conj,gana_pada) = extract_gana_pada morph in
  if conj=Primary then attested_verb gana_pada pv root else attested pv root
  with [ Unvoiced -> attested pv root ]
and valid_morph_aut root (morph : Morphology.inflexion_tag) = try
  let (conj,gana_pada) = extract_gana_pada morph in
  if conj=Primary then autonomous_root gana_pada root 
                  else autonomous root (* eg. kalpaya Para ca. while k.lp Atma *)
  with [ Unvoiced -> autonomous root ]
;
value valid_morph_pv_k pv krit_stem morph = (* morph of form [Part_form] *)
  let (homo,bare_stem) = homo_undo krit_stem in  
  let krit_infos = assoc_word bare_stem unique_kridantas in  
  let ((conj,krit),root) = look_up_homo homo krit_infos in try
  (* Asymmetry of treatment: conj is deduced from [krit_stem], not from morph *)
  let gana_pada = extract_gana_pada_k krit in 
  if conj=Primary then attested_verb gana_pada pv root else attested pv root 
  with [ Unvoiced -> attested pv root ]
;
value validate_pv pv root_form = (* generalizes [roots_of] *) 
  match Deco.assoc root_form morpho.roots with
    [ [] -> fail_inconsistency root_form
    | tags -> List.exists valid tags 
              (* NB later on the lexer will refine in filtering validity *)
              where valid (delta,morphs) = 
                let root = Word.patch delta root_form in  
                List.exists (valid_morph_pv pv root) morphs
    ]  
;
value validate_pv_tu pv root_form = (* special case infinitive forms in -tu *) 
  match Deco.assoc root_form morpho.inftu with
    [ [] -> fail_inconsistency root_form
    | tags -> List.exists valid tags 
              (* NB later on the lexer will refine in filtering validity *)
              where valid (delta,morphs) = 
                let root = Word.patch delta root_form in  
                List.exists (valid_morph_pv pv root) morphs
    ]  
;
value validate_pv_k pv krit_form (delta,_) = (* see [Morpho.print_inv_morpho] *)
  let krit_stem = Word.patch delta krit_form in 
  let (homo,bare_stem) = homo_undo krit_stem in 
  let krit_infos = assoc_word bare_stem unique_kridantas in 
  let ((conj,krit),root) = look_up_homo homo krit_infos in try
  let gana_pada = extract_gana_pada_k krit in  
  if conj=Primary then attested_verb gana_pada pv root else attested pv root
  with [ Unvoiced -> attested pv root ]
;
(* We should verify aa- validation for phantomatic forms *)
value autonomous_form root_form = 
  match Deco.assoc root_form morpho.roots with
    [ [] -> fail_inconsistency root_form
    | tags -> List.exists valid tags (* Lexer will filter later on *)
      where valid (delta,morphs) = 
        let root = Word.patch delta root_form in
        List.exists (valid_morph_aut root) morphs 
    ]  
;
(* This allows to rule out ifc only kridantas even when root autonomous *)
value filter_out_krit krit root = match Canon.decode root with
  [ "i" | "dagh" -> krit = Ppp (* -ita -daghna *)
  | _ -> False
  ] 
;
(* We should verify aa- validation for phantomatic forms *)
value autonomous_form_k krid_form (delta,_) =
  let stem = Word.patch delta krid_form in
  let (homo,bare_stem) = homo_undo stem in
  let krid_infos = assoc_word bare_stem unique_kridantas in 
  let ((conj,krit),root) = look_up_homo homo krid_infos in try
  let gana_pada = extract_gana_pada_k krit in  
  if conj=Primary then if filter_out_krit krit root then False
                       else autonomous_root gana_pada root else True
  with [ Unvoiced -> autonomous root ]
;
(* Checks whether a verbal or participial form is attested/validated *)
value valid_morpho gen = 
  if gen then valid_morph_pv_k else valid_morph_pv 
;
(* This inspects a multitag in order to filter out pv-inconsistent taggings. *)
(* It is used by Interface and Lexer for Reader and Parser *)
value trim_tags gen form pv tags = List.fold_right trim tags []
      where trim (delta,morphs) acc = (* tags : Morphology.multitag *)  
        let stem = Word.patch delta form in (* root or kridanta *)
        let valid_pv = valid_morpho gen pv stem in 
        let ok_morphs = List.filter valid_pv morphs in  
        if ok_morphs = [] then acc else [ (delta,ok_morphs) :: acc ] 
;
(* Preventing overgeneration of forms "sa" and "e.sa" \Pan{6,1,132} *)
value not_sa_v = fun (* Assumes next pada starts with a vowel *)
  [ [ (Pron,[ 1; 48 ],_) :: _ ] (* sa *)
  | [ (Pron,[ 1; 47; 10 ],_) :: _ ] (* e.sa *) -> False 
  | _ -> True
  ]
and sa_before_check form = fun (* Next pada should start with a consonant *)
  [ [ (Pron,[ 1; 48 ],_) :: _ ] (* sa *)
  | [ (Pron,[ 1; 47; 10 ],_) :: _ ] (* e.sa *) -> Phonetics.consonant_initial form
  | _ -> True
  ]
;
(* Similar to [List2.subtract] but raises Anomaly exception *)
value rec chop word = fun  
  [ [] -> word
  | [ c :: r ] -> match word with 
     [ [ c' :: r' ] when c'=c -> chop r' r
     | _ -> raise (Control.Anomaly "Wrong transition between segments")
     ]
  ]
; 
value sfx_phase = fun [ Sfx | Isfx -> True | _ -> False ]
and iic_phase = fun 
  [ Iicv | Iicc | Iikv | Iikc 
  | Comp (_,Iikv) _ _ | Comp (_,Iikc) _ _ -> True
  | _ -> False ]
;
value apply_sandhi rleft right = fun
    [ Euphony (w,ru,v) -> 
       let rl = chop rleft ru
       and r =  chop right v in List2.unstack rl (w @ r)
    | Id -> List2.unstack rleft right
    ]
;
(* [validate : output -> output] - dynamic consistency check in Segmenter.
   It refines the regular language of dispatch by contextual conditions
   expressing that preverbs are consistent with the following verbal form. 
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   The forms are then compounded, otherwise rejected. *)
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(* Things would be much simpler if we generated forms of verbs and kridantas
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 with (only valid) preverbs attached, since this check would be unnecessary.
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 On the other hand, we would have to solve the ihehi problem. *)
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(* A similar kind of aggregation is effected for a few generative taddhitas,
   but this is still experimental. *)
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value validate out = match out with
  [ [] -> []
  | [ (Root,rev_root_form,s) :: [ (Pv,prev,sv) :: r ] ] ->
      let pv = Word.mirror prev in 
      let pv_str = Canon.decode pv 
      and root_form = Word.mirror rev_root_form in
      if validate_pv pv_str root_form then  
         let form = apply_sandhi prev root_form sv in
         let verb_form = Word.mirror form in
         (* We glue the two segments with a composite tag keeping information *)
         [ (Comp (Pv,Root) pv root_form,verb_form,s) :: r ] 
      else []
  | [ (Root,rev_root_form,_) :: next ] ->
      let root_form = Word.mirror rev_root_form in 
      if autonomous_form root_form && sa_before_check root_form next
      then out else [] 
  | [ (Lopa,rev_lopa_form,s) :: [ (Pv,prev,sv) :: r ] ] -> 
      let pv = Word.mirror prev in 
      let pv_str = Canon.decode pv 
      and lopa_form = Word.mirror rev_lopa_form in
      let root_form = match lopa_form with 
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                      [ [ -2 :: rf ] -> rf 
                      | _ -> failwith "Wrong lopa form" 
                      ] in
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      if validate_pv pv_str root_form then
        let form = apply_sandhi prev lopa_form sv in
        let verb_form = Word.mirror form in
        [ (Comp (Pv,Lopa) pv lopa_form,verb_form,s) :: r ] 
      else []
  | [ (Lopa,rev_lopa_form,_) :: next ] ->
      let lopa_form = Word.mirror rev_lopa_form in 
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      if autonomous_form lopa_form && sa_before_check lopa_form next
         then out else []
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  | (* infinitives in -tu with preverbs *)
    [ (Inftu,rev_root_form,s) :: [ (Pv,prev,sv) :: r ] ] ->
      let pv = Word.mirror prev in 
      let pv_str = Canon.decode pv 
      and root_form = Word.mirror rev_root_form in
      if validate_pv_tu pv_str root_form then  
         let form = apply_sandhi prev root_form sv in
         let verb_form = Word.mirror form in
         (* We glue the two segments with a composite tag keeping information *)
         [ (Comp (Pv,Inftu) pv root_form,verb_form,s) :: r ] 
      else []
   | (* kridanta forms with preverbs *)
     [ (phk,rev_krid_form,s) :: [ (ph,prev,sv) :: r ] ] 
         when krid_phase phk && preverb_phase ph ->
      let pv = Word.mirror prev in 
      let pv_str = Canon.decode pv 
      and krid_form = Word.mirror rev_krid_form in
      match Deco.assoc krid_form morpho.krids with
      [ [] -> failwith ("Unknown krid_form: " ^ Canon.decode krid_form)
      | tags -> if List.exists (validate_pv_k pv_str krid_form) tags then
                   let form = apply_sandhi prev krid_form sv in
                   let cpd_form = Word.mirror form in
                   [ (Comp (ph,phk) pv krid_form,cpd_form,s) :: r ] 
                else []
      ]
  | [ (Kriv,rev_krid_form,_) :: next ] ->
      let krid_form = Word.mirror rev_krid_form in
      if phantomatic krid_form then failwith "Kriv phantom" else (* PB *)
      match Deco.assoc krid_form morpho.krids with
      [ [] -> failwith ("Unknown krid_form: " ^ Canon.decode krid_form) 
      | tags -> if List.exists (autonomous_form_k krid_form) tags && not_sa_v next
                then out else []
      ]
  | [ (Kric,rev_krid_form,_) :: _ ] ->
      let krid_form = Word.mirror rev_krid_form in
      match Deco.assoc krid_form morpho.krids with
      [ [] -> failwith ("Unknown krid_form: " ^ (Canon.decode krid_form))
      | tags -> if List.exists (autonomous_form_k krid_form) tags
                then out else []
      ]
   | (* iic kridanta forms with preverbs *)
     [ (phk,rev_ikrid_form,s) :: [ (ph,prev,sv) :: r ] ] 
         when ikrid_phase phk && preverb_phase ph ->
      let pv = Word.mirror prev in 
      let pv_str = Canon.decode pv 
      and ikrid_form = Word.mirror rev_ikrid_form in
      match Deco.assoc ikrid_form morpho.iiks with
      [ [] -> failwith ("Unknown ikrid_form: " ^ Canon.decode ikrid_form)
      | tags -> if List.exists (validate_pv_k pv_str ikrid_form) tags then
                   let form = apply_sandhi prev ikrid_form sv in
                   let cpd_form = Word.mirror form in
                   [ (Comp (ph,phk) pv ikrid_form,cpd_form,s) :: r ] 
                else []
      ]
  | [ (Iikv,rev_krid_form,_) :: next ] ->
      let krid_form = Word.mirror rev_krid_form in
      match Deco.assoc krid_form morpho.iiks with
      [ [] -> failwith ("Unknown krid_form: " ^ Canon.decode krid_form)
      | tags -> if List.exists (autonomous_form_k krid_form) tags && not_sa_v next
                then out else []
      ]
  | [ (Iikc,rev_krid_form,_) :: _ ] ->
      let krid_form = Word.mirror rev_krid_form in
      match Deco.assoc krid_form morpho.iiks with
      [ [] -> failwith ("Unknown krid_form: " ^ Canon.decode krid_form)
      | tags -> if List.exists (autonomous_form_k krid_form) tags
                then out else []
      ]
  | (* vocative kridanta forms with preverbs *)
    [ (phk,rev_krid_form,s) :: [ (ph,prev,sv) :: r ] ] 
         when vkrid_phase phk && preverb_phase ph ->
      let pv = Word.mirror prev in 
      let pv_str = Canon.decode pv 
      and krid_form = Word.mirror rev_krid_form in
      match Deco.assoc krid_form morpho.voks with
      [ [] -> failwith ("Unknown krid_form: " ^ Canon.decode krid_form)
      | tags -> if List.exists (validate_pv_k pv_str krid_form) tags then
                   let form = apply_sandhi prev krid_form sv in
                   let cpd_form = Word.mirror form in
                   [ (Comp (ph,phk) pv krid_form,cpd_form,s) :: r ] 
                else []
      ]
  | [ (Vokv,rev_krid_form,_) :: next ] ->
      let krid_form = Word.mirror rev_krid_form in
      match Deco.assoc krid_form morpho.voks with
      [ [] -> failwith ("Unknown krid_form: " ^ Canon.decode krid_form)
      | tags -> if List.exists (autonomous_form_k krid_form) tags && not_sa_v next
                then out else []
      ]
  | [ (Vokc,rev_krid_form,_) :: _ ] ->
      let krid_form = Word.mirror rev_krid_form in
      match Deco.assoc krid_form morpho.voks with
      [ [] -> failwith ("Unknown krid_form: " ^ Canon.decode krid_form)
      | tags -> if List.exists (autonomous_form_k krid_form) tags
                then out else []
      ]
  | [ (Lopak,rev_lopak_form,s) :: [ (ph,prev,sv) :: r ] ]  
        when preverb_phase ph ->
      let pv = Word.mirror prev in 
      let pv_str = Canon.decode pv 
      and lopak_form = Word.mirror rev_lopak_form in
      let krid_form = match lopak_form with 
                      [ [ -2 :: rf ] -> rf | _ -> failwith "Wrong lopa form" ] in
      match Deco.assoc krid_form morpho.lopaks with
      [ [] -> failwith ("Unknown krid_form: " ^ Canon.decode krid_form)
      | tags -> if List.exists (validate_pv_k pv_str krid_form) tags then
                   let form = apply_sandhi prev krid_form sv in
                   let cpd_form = Word.mirror form in
                   [ (Comp (ph,Lopak) pv krid_form,cpd_form,s) :: r ]
                else []
      ] (*i TODO Lopak without preverb i*)
  | [ (Peri,rev_peri_form,s) :: [ (Pv,prev,sv) :: r ] ] -> 
      let pv = Word.mirror prev in 
      let pv_str = Canon.decode pv 
      and peri_form = Word.mirror rev_peri_form in
      match Deco.assoc peri_form morpho.peris with
      [ [] -> failwith ("Unknown peri_form: " ^ Canon.decode peri_form)
      | tags -> let valid (delta,morphs) = 
                   let root = Word.patch delta peri_form in
                   attested pv_str root in 
                if List.exists valid tags then
                   let form = apply_sandhi prev peri_form sv in 
                   let cpd_form = Word.mirror form in
                   [ (Comp (Pv,Peri) pv peri_form,cpd_form,s) :: r ]
                else []
      ]
  | [ (Abso,rev_abso_form,s) :: [ (Pv,prev,sv) :: r ] ] ->
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      (* Takes care of absolutives in -ya *)
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      let pv = Word.mirror prev in 
      let pv_str = Canon.decode pv 
      and abso_form = Word.mirror rev_abso_form in
      match Deco.assoc abso_form morpho.absya with
      [ [] -> failwith ("Unknown abs_form: " ^ Canon.decode abso_form)
      | tags -> let valid (delta,morphs) = 
                   let root = Word.patch delta abso_form in
                   attested pv_str root in 
                if List.exists valid tags then
                   let form = apply_sandhi prev abso_form sv in 
                   let cpd_form = Word.mirror form in
                   [ (Comp (Pv,Abso) pv abso_form,cpd_form,s) :: r ]
                else []
      ]
    (* We now prevent overgeneration of forms "sa" and "e.sa" \Pan{6,1,132} *)
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  | [ (ph,form,_) :: [ (Pron,[ 1; 48 ],_) :: _ ] ] (* sa *) -> 
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      if Phonetics.consonant_initial (Word.mirror form)  
      then out else [] 
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    (* Or, if one wants to replace sa with sa.h : [
  | [ ((ph,form,_) as last) :: [ (Pron,[ 1; 48 ],_) :: rest ] ] (* sa *) -> 
      let initial = List.hd (Word.mirror form) in 
      if Phonetics.consonant initial then 
         let sandhi = Euphony ([ 48; 1; initial], [ 48; 1; 48 ], [ initial ]) in
         [ last :: [ (Pron,[ 48; 1; 48 ],sandhi) :: rest ] ] 
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      else [] ] - But we should do it between chunks as well *)
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  | [ (ph,form,_) :: [ (Pron,[ 1; 47; 10 ],_) :: _ ] ] (* e.sa *) ->
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      if Phonetics.consonant_initial (Word.mirror form)  
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      then out else [] 
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  | [ (ph,form,_) :: [ (Pron,[ 48; 1; 48 ],_) :: _ ] ] (* sas *) ->  
      if Phonetics.consonant_initial (Word.mirror form) then [] 
      else out 
  | [ (ph,form,_) :: [ (Pron,[ 48; 1; 47; 10 ],_) :: _ ] ] (* e.sas *) ->  
      if Phonetics.consonant_initial (Word.mirror form) then [] 
      else out 
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    (*i TODO: similar test for dual forms i*)
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(* Finally we glue taddita suffix "forms" to the previous (iic) segment *)
(* NB This cumulates with the preverb glueing but not with itself *)
  | [ (sfxph,sfx,s) :: [ (ph,rstem,sv) :: r ] ] when sfx_phase sfxph 
                                                  && iic_phase ph ->
      let sfx_form = Word.mirror sfx in 
      let stem = Word.mirror rstem in
      let tad_form = Word.mirror (apply_sandhi rstem sfx_form sv) in
      [ (Tad (ph,sfxph) stem sfx_form,tad_form,s) :: r ]
  | [ (phase,_,_) :: [ (pv,_,_) :: _ ] ] when preverb_phase pv -> 
      let m = "validate: " ^ string_of_phase pv ^ " " ^ string_of_phase phase in 
      raise (Control.Anomaly m) (* all preverbs ought to have been processed *)
(* [ | [ (pv,_,_) :: _ ] when preverb_phase pv -> out ] noop
This pv is not terminal, and should be chopped off by the next item *) 
  | [ _ :: [ (_,w,_) :: _ ] ] when phantomatic (Word.mirror w) -> 
    raise (Control.Anomaly "Bug phantomatic segment")
  | _ -> out (* default identity *)
  ]
;
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value terminal_sa = fun 
  [ [ (Pron,[ 1; 48 ],_) :: _ ] (* sa *) 
  | [ (Pron,[ 1; 47; 10 ],_) :: _ ] (* e.sa *) -> True
  | _ -> False 
  ]
;
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(*i unused [
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value terminal_sas = fun 
  [ [ (Pron,[ 48; 1; 48 ],_) :: _ ] (* sas *)  
  | [ (Pron,[ 48; 1; 47; 10 ],_) :: _ ] (* e.sas *) -> True 
  | _ -> False 
  ]
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; ] i*)
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open Html;
value rec color_of_phase = fun
  [ Noun | Noun2 | Lopak | Nouc | Nouv | Kriv | Kric | Krid | Auxik | Kama
         | Cache -> Deep_sky 
  | Pron -> Light_blue
  | Root | Auxi | Lopa -> Carmin  
  | Inde | Abso | Absv | Absc | Ai | Ani -> Mauve
  | Iiy -> Lavender
  | Avy -> Magenta
  | Inftu -> Salmon 
  | Iic | Iic2 | A | An | Iicv | Iicc | Iik | Iikv | Iikc | Iiif 
        -> Yellow
  | Auxiick | Iivv | Iivc | Peri | Iiv -> Orange
  | Voca | Vocv | Vocc | Inv | Vok | Vokv | Vokc -> Lawngreen
  | Ifc | Ifc2 -> Cyan
  | Unknown -> Grey
  | Comp (_,ph) _ _ -> color_of_phase ph 
  | Tad (_,ph)  _ _ -> if ph=Sfx then Deep_sky else Yellow
  | Pv | Pvk | Pvkc | Pvkv -> failwith "Illegal preverb segment"
  | Sfx -> Deep_sky (* necessary for [Lexer.print_segment2] *)
  | Isfx -> Yellow  (* idem *)
(*i NB: unused background colors: Pink Green Aquamarine Chamois i*)
  ]
; 

end;