!  To simplify the picture a little, a rough map of the main routine:
!
!  (A)    Get the input, do "oops" and "again"
!  (B)    Is it a direction, and so an implicit "go"?  If so go to (K)
!  (C)    Is anyone being addressed?
!  (D)    Get the verb: try all the syntax lines for that verb
!  (E)    Break down a syntax line into analysed tokens
!  (F)    Look ahead for advance warning for multiexcept/multiinside
!  (G)    Parse each token in turn (calling ParseToken to do most of the work)
!  (H)    Cheaply parse otherwise unrecognised conversation and return
!  (I)    Print best possible error message
!  (J)    Retry the whole lot
!  (K)    Last thing: check for "then" and further instructions(s), return.
!
!  The strategic points (A) to (K) are marked in the commentary.
!
!  Note that there are three different places where a return can happen.
! ----------------------------------------------------------------------------

[ Parser__parse  results   syntax line num_lines line_address i j k
                           token l m;

!  **** (A) ****

!  Firstly, in "not held" mode, we still have a command left over from last
!  time (eg, the user typed "eat biscuit", which was parsed as "take biscuit"
!  last time, with "eat biscuit" tucked away until now).  So we return that.

    if (notheld_mode==1)
    {   for (i=0:i<8:i++) results-->i=kept_results-->i;
        notheld_mode=0; rtrue;
    }

    if (held_back_mode==1)
    {   held_back_mode=0;
        Tokenise__(buffer,parse);
        jump ReParse;
    }

  .ReType;

    Keyboard(buffer,parse);

  .ReParse;

    parser_inflection = name;

!  Initially assume the command is aimed at the player, and the verb
!  is the first word

    num_words=parse->1;
    wn=1;
#ifdef LanguageToInformese;
    LanguageToInformese();
#ifv5;
!   Re-tokenise:
    Tokenise__(buffer,parse);
#endif;
#endif;

    BeforeParsing();
    num_words=parse->1;

    k=0;
#ifdef DEBUG;
    if (parser_trace>=2)
    {   print "[ ";
        for (i=0:i<num_words:i++)
        {   j=parse-->(i*2 + 1);
            k=WordAddress(i+1);
            l=WordLength(i+1);
            print "~"; for (m=0:m<l:m++) print (char) k->m; print "~ ";

            if (j == 0) print "?";
            else
            {   if (UnsignedCompare(j, 0-->4)>=0
                    && UnsignedCompare(j, 0-->2)<0) print (address) j;
                else print j;
            }
            if (i ~= num_words-1) print " / ";
        }
        print " ]^";
    }
#endif;
    verb_wordnum=1;
    actor=player;
    actors_location = ScopeCeiling(player);
    usual_grammar_after = 0;

  .AlmostReParse;

    scope_token = 0;
    action_to_be = NULL;

!  Begin from what we currently think is the verb word

  .BeginCommand;
    wn=verb_wordnum;
    verb_word = NextWordStopped();

!  If there's no input here, we must have something like
!  "person,".

    if (verb_word==-1)
    {   best_etype = STUCK_PE; jump GiveError; }

!  Now try for "again" or "g", which are special cases:
!  don't allow "again" if nothing has previously been typed;
!  simply copy the previous text across

    if (verb_word==AGAIN2__WD or AGAIN3__WD) verb_word=AGAIN1__WD;
    if (verb_word==AGAIN1__WD)
    {   if (actor~=player)
        {   L__M(##Miscellany,20); jump ReType; }
        if (buffer3->1==0)
        {   L__M(##Miscellany,21); jump ReType; }
        for (i=0:i<120:i++) buffer->i=buffer3->i;
        jump ReParse;
    }

!  Save the present input in case of an "again" next time

    if (verb_word~=AGAIN1__WD)
        for (i=0:i<120:i++) buffer3->i=buffer->i;

    if (usual_grammar_after==0)
    {   i = RunRoutines(actor, grammar);
        #ifdef DEBUG;
        if (parser_trace>=2 && actor.grammar~=0 or NULL)
            print " [Grammar property returned ", i, "]^";
        #endif;
        if (i<0) { usual_grammar_after = verb_wordnum; i=-i; }
        if (i==1)
        {   results-->0 = action;
            results-->1 = noun;
            results-->2 = second;
            rtrue;
        }
        if (i~=0) { verb_word = i; wn--; verb_wordnum--; }
        else
        {   wn = verb_wordnum; verb_word=NextWord();
        }
    }
    else usual_grammar_after=0;

!  **** (B) ****

    #ifdef LanguageIsVerb;
    if (verb_word==0)
    {   i = wn; verb_word=LanguageIsVerb(buffer, parse, verb_wordnum);
        wn = i;
    }
    #endif;

!  If the first word is not listed as a verb, it must be a direction
!  or the name of someone to talk to

    if (verb_word==0 || ((verb_word->#dict_par1) & 1) == 0)
    {   

!  So is the first word an object contained in the special object "compass"
!  (i.e., a direction)?  This needs use of NounDomain, a routine which
!  does the object matching, returning the object number, or 0 if none found,
!  or REPARSE_CODE if it has restructured the parse table so the whole parse
!  must be begun again...

        wn=verb_wordnum; indef_mode = false; token_filter = 0;
        l=NounDomain(compass,0,0); if (l==REPARSE_CODE) jump ReParse;

!  If it is a direction, send back the results:
!  action=GoSub, no of arguments=1, argument 1=the direction.

        if (l~=0)
        {   results-->0 = ##Go;
            action_to_be = ##Go;
            results-->1 = 1;
            results-->2 = l;
            jump LookForMore;
        }

!  **** (C) ****

!  Only check for a comma (a "someone, do something" command) if we are
!  not already in the middle of one.  (This simplification stops us from
!  worrying about "robot, wizard, you are an idiot", telling the robot to
!  tell the wizard that she is an idiot.)

        if (actor==player)
        {   for (j=2:j<=num_words:j++)
            {   i=NextWord(); if (i==comma_word) jump Conversation;
            }

            verb_word=UnknownVerb(verb_word);
            if (verb_word~=0) jump VerbAccepted;
        }

        best_etype=VERB_PE; jump GiveError;

!  NextWord nudges the word number wn on by one each time, so we've now
!  advanced past a comma.  (A comma is a word all on its own in the table.)

      .Conversation;
        j=wn-1;
        if (j==1) { L__M(##Miscellany,22); jump ReType; }

!  Use NounDomain (in the context of "animate creature") to see if the
!  words make sense as the name of someone held or nearby

        wn=1; lookahead=HELD_TOKEN;
        scope_reason = TALKING_REASON;
        l=NounDomain(player,actors_location,6);
        scope_reason = PARSING_REASON;
        if (l==REPARSE_CODE) jump ReParse;

        if (l==0) { L__M(##Miscellany,23); jump ReType; }

!  The object addressed must at least be "talkable" if not actually "animate"
!  (the distinction allows, for instance, a microphone to be spoken to,
!  without the parser thinking that the microphone is human).

        if (l hasnt animate && l hasnt talkable)
        {   L__M(##Miscellany, 24, l); jump ReType; }

!  Check that there aren't any mystery words between the end of the person's
!  name and the comma (eg, throw out "dwarf sdfgsdgs, go north").

        if (wn~=j)
        {   L__M(##Miscellany, 25); jump ReType; }

!  The player has now successfully named someone.  Adjust "him", "her", "it":

        PronounNotice(l);

!  Set the global variable "actor", adjust the number of the first word,
!  and begin parsing again from there.

        verb_wordnum=j+1;

!  Stop things like "me, again":

        if (l == player)
        {   wn = verb_wordnum;
            if (NextWordStopped() == AGAIN1__WD or AGAIN2__WD or AGAIN3__WD)
            {   L__M(##Miscellany,20); jump ReType;
            }
        }

        actor=l;
        actors_location=ScopeCeiling(l);
        #ifdef DEBUG;
        if (parser_trace>=1)
            print "[Actor is ", (the) actor, " in ",
                (name) actors_location, "]^";
        #endif;
        jump BeginCommand;
    }

!  **** (D) ****

   .VerbAccepted;

!  We now definitely have a verb, not a direction, whether we got here by the
!  "take ..." or "person, take ..." method.  Get the meta flag for this verb:

    meta=((verb_word->#dict_par1) & 2)/2;

!  You can't order other people to "full score" for you, and so on...

    if (meta==1 && actor~=player)
    {   best_etype=VERB_PE; meta=0; jump GiveError; }

!  Now let i be the corresponding verb number, stored in the dictionary entry
!  (in a peculiar 255-n fashion for traditional Infocom reasons)...

    i=$ff-(verb_word->#dict_par2);

!  ...then look up the i-th entry in the verb table, whose address is at word
!  7 in the Z-machine (in the header), so as to get the address of the syntax
!  table for the given verb...

    syntax=(0-->7)-->i;

!  ...and then see how many lines (ie, different patterns corresponding to the
!  same verb) are stored in the parse table...

    num_lines=(syntax->0)-1;

!  ...and now go through them all, one by one.
!  To prevent pronoun_word 0 being misunderstood,

   pronoun_word=NULL; pronoun_obj=NULL;

   #ifdef DEBUG;
   if (parser_trace>=1)
   {    print "[Parsing for the verb '", (address) verb_word,
              "' (", num_lines+1, " lines)]^";
   }
   #endif;

   best_etype=STUCK_PE; nextbest_etype=STUCK_PE;

!  "best_etype" is the current failure-to-match error - it is by default
!  the least informative one, "don't understand that sentence".
!  "nextbest_etype" remembers the best alternative to having to ask a
!  scope token for an error message (i.e., the best not counting ASKSCOPE_PE).


!  **** (E) ****

    line_address = syntax + 1;

    for (line=0:line<=num_lines:line++)
    {   
        for (i = 0 : i < 32 : i++)
        {   line_token-->i = ENDIT_TOKEN;
            line_ttype-->i = ELEMENTARY_TT;
            line_tdata-->i = ENDIT_TOKEN;
        }

!  Unpack the syntax line from Inform format into three arrays; ensure that
!  the sequence of tokens ends in an ENDIT_TOKEN.

        line_address = UnpackGrammarLine(line_address);
            
        #ifdef DEBUG;
        if (parser_trace >= 1)
        {   if (parser_trace >= 2) new_line;
            print "[line ", line; DebugGrammarLine();
            print "]^";
        }
        #endif;

!  We aren't in "not holding" or inferring modes, and haven't entered
!  any parameters on the line yet, or any special numbers; the multiple
!  object is still empty.

        not_holding=0;
        inferfrom=0;
        parameters=0;
        nsns=0; special_word=0; special_number=0;
        multiple_object-->0 = 0;
        multi_context = 0;
        etype=STUCK_PE;

!  Put the word marker back to just after the verb

        wn=verb_wordnum+1;

!  **** (F) ****
!  There are two special cases where parsing a token now has to be
!  affected by the result of parsing another token later, and these
!  two cases (multiexcept and multiinside tokens) are helped by a quick
!  look ahead, to work out the future token now.  We can only carry this
!  out in the simple (but by far the most common) case:
!
!      multiexcept <one or more prepositions> noun
!
!  and similarly for multiinside.

        advance_warning = NULL; indef_mode = false;
        for (i=0,m=false,pcount=0:line_token-->pcount ~= ENDIT_TOKEN:pcount++)
        {   scope_token = 0;

            if (line_ttype-->pcount ~= PREPOSITION_TT) i++;

            if (line_ttype-->pcount == ELEMENTARY_TT)
            {   if (line_tdata-->pcount == MULTI_TOKEN) m=true;
                if (line_tdata-->pcount
                    == MULTIEXCEPT_TOKEN or MULTIINSIDE_TOKEN  && i==1)
                {   !   First non-preposition is "multiexcept" or
                    !   "multiinside", so look ahead.

                    #ifdef DEBUG;
                    if (parser_trace>=2) print " [Trying look-ahead]^";
                    #endif;

                    !   We need this to be followed by 1 or more prepositions.

                    pcount++;
                    if (line_ttype-->pcount == PREPOSITION_TT)
                    {   while (line_ttype-->pcount == PREPOSITION_TT)
                            pcount++;

                        if ((line_ttype-->pcount == ELEMENTARY_TT)
                            && (line_tdata-->pcount == NOUN_TOKEN))
                        {
                            !  Advance past the last preposition

                            while (wn <= num_words)
                            {   if (NextWord() == line_tdata-->(pcount-1))
                                {   l = NounDomain(actors_location, actor,
                                            NOUN_TOKEN);
                                    #ifdef DEBUG;
                                    if (parser_trace>=2)
                                    {   print " [Advanced to ~noun~ token: ";
                                        if (l==REPARSE_CODE)
                                            print "re-parse request]^";
                                        if (l==1) print "but multiple found]^";
                                        if (l==0) print "error ", etype, "]^";
                                        if (l>=2) print (the) l, "]^";
                                    }
                                    #endif;
                                    if (l==REPARSE_CODE) jump ReParse;
                                    if (l>=2) advance_warning = l;
                                }
                            }
                        }
                    }
                    break;
                }
            }
        }

!  Slightly different line-parsing rules will apply to "take multi", to
!  prevent "take all" behaving correctly but misleadingly when there's
!  nothing to take.

        take_all_rule = 0;
        if (m && params_wanted==1 && action_to_be==##Take)
            take_all_rule = 1;

!  And now start again, properly, forearmed or not as the case may be.
!  As a precaution, we clear all the variables again (they may have been
!  disturbed by the call to NounDomain, which may have called outside
!  code, which may have done anything!).

        not_holding=0;
        inferfrom=0;
        parameters=0;
        nsns=0; special_word=0; special_number=0;
        multiple_object-->0 = 0;
        etype=STUCK_PE;
        wn=verb_wordnum+1;

!  **** (G) ****
!  "Pattern" gradually accumulates what has been recognised so far,
!  so that it may be reprinted by the parser later on

        for (pcount=1::pcount++)
        {   pattern-->pcount = PATTERN_NULL; scope_token=0;

            token = line_token-->(pcount-1);
            lookahead = line_token-->pcount;

            #ifdef DEBUG;
            if (parser_trace >= 2)
               print " [line ", line, " token ", pcount, " word ", wn, " : ",
                     (DebugToken) token, "]^";
            #endif;

            if (token ~= ENDIT_TOKEN)
            {   scope_reason = PARSING_REASON;
                parser_inflection = name;
                AnalyseToken(token);
                l = ParseToken__(found_ttype, found_tdata, pcount-1, token);
                while (l<-200) l = ParseToken__(ELEMENTARY_TT, l + 256);
                scope_reason = PARSING_REASON;

                if (l==GPR_PREPOSITION)
                {   if (found_ttype~=PREPOSITION_TT
                        && (found_ttype~=ELEMENTARY_TT
                            || found_tdata~=TOPIC_TOKEN)) params_wanted--;
                    l = true;
                }
                else
                if (l<0) l = false;
                else
                if (l~=GPR_REPARSE)
                {   if (l==GPR_NUMBER)
                    {   if (nsns==0) special_number1=parsed_number;
                        else special_number2=parsed_number;
                        nsns++; l = 1;
                    }
                    if (l==GPR_MULTIPLE) l = 0;
                    results-->(parameters+2) = l;
                    parameters++;
                    pattern-->pcount = l;
                    l = true;
                }

                #ifdef DEBUG;
                if (parser_trace >= 3)
                {   print "  [token resulted in ";
                    if (l==REPARSE_CODE) print "re-parse request]^";
                    if (l==0) print "failure with error type ", etype, "]^";
                    if (l==1) print "success]^";
                }
                #endif;

                if (l==REPARSE_CODE) jump ReParse;
                if (l==false) break;
            }
            else
            {

!  If the player has entered enough already but there's still
!  text to wade through: store the pattern away so as to be able to produce
!  a decent error message if this turns out to be the best we ever manage,
!  and in the mean time give up on this line

!  However, if the superfluous text begins with a comma or "then" then
!  take that to be the start of another instruction

                if (wn <= num_words)
                {   l=NextWord();
                    if (l==THEN1__WD or THEN2__WD or THEN3__WD or comma_word)
                    {   held_back_mode=1; hb_wn=wn-1; }
                    else
                    {   for (m=0:m<32:m++) pattern2-->m=pattern-->m;
                        pcount2=pcount;
                        etype=UPTO_PE; break;
                    }
                }

!  Now, we may need to revise the multiple object because of the single one
!  we now know (but didn't when the list was drawn up).

                if (parameters>=1 && results-->2 == 0)
                {   l=ReviseMulti(results-->3);
                    if (l~=0) { etype=l; break; }
                }
                if (parameters>=2 && results-->3 == 0)
                {   l=ReviseMulti(results-->2);
                    if (l~=0) { etype=l; break; }
                }

!  To trap the case of "take all" inferring only "yourself" when absolutely
!  nothing else is in the vicinity...

                if (take_all_rule==2 && results-->2 == actor)
                {   best_etype = NOTHING_PE; jump GiveError;
                }

                #ifdef DEBUG;
                if (parser_trace>=1)
                    print "[Line successfully parsed]^";
                #endif;

!  The line has successfully matched the text.  Declare the input error-free...

                oops_from = 0;

!  ...explain any inferences made (using the pattern)...

                if (inferfrom~=0)
                {   print "("; PrintCommand(inferfrom); print ")^";
                }

!  ...copy the action number, and the number of parameters...

                results-->0 = action_to_be;
                results-->1 = parameters;

!  ...reverse first and second parameters if need be...

                if (action_reversed && parameters==2)
                {   i = results-->2; results-->2 = results-->3;
                    results-->3 = i;
                    if (nsns == 2)
                    {   i = special_number1; special_number1=special_number2;
                        special_number2=i;
                    }
                }

!  ...and to reset "it"-style objects to the first of these parameters, if
!  there is one (and it really is an object)...

                if (parameters > 0 && results-->2 >= 2)
                    PronounNotice(results-->2);

!  ...and worry about the case where an object was allowed as a parameter
!  even though the player wasn't holding it and should have been: in this
!  event, keep the results for next time round, go into "not holding" mode,
!  and for now tell the player what's happening and return a "take" request
!  instead...

                if (not_holding~=0 && actor==player)
                {   notheld_mode=1;
                    for (i=0:i<8:i++) kept_results-->i = results-->i;
                    results-->0 = ##Take;
                    results-->1 = 1;
                    results-->2 = not_holding;
                    L__M(##Miscellany, 26, not_holding);
                }

!  (Notice that implicit takes are only generated for the player, and not
!  for other actors.  This avoids entirely logical, but misleading, text
!  being printed.)

!  ...and return from the parser altogether, having successfully matched
!  a line.

                if (held_back_mode==1) { wn=hb_wn; jump LookForMore; }
                rtrue;
            }
        }

!  The line has failed to match.
!  We continue the outer "for" loop, trying the next line in the grammar.

        if (etype>best_etype) best_etype=etype;
        if (etype~=ASKSCOPE_PE && etype>nextbest_etype) nextbest_etype=etype;

!  ...unless the line was something like "take all" which failed because
!  nothing matched the "all", in which case we stop and give an error now.

        if (take_all_rule == 2 && etype==NOTHING_PE) break;
   }

!  The grammar is exhausted: every line has failed to match.

!  **** (H) ****

  .GiveError;
        etype=best_etype;

!  Errors are handled differently depending on who was talking.

!  If the command was addressed to somebody else (eg, "dwarf, sfgh") then
!  it is taken as conversation which the parser has no business in disallowing.

    if (actor~=player)
    {   if (usual_grammar_after>0)
        {   verb_wordnum = usual_grammar_after;
            jump AlmostReParse;
        }
        wn=verb_wordnum;
        special_word=NextWord();
        if (special_word==comma_word)
        {   special_word=NextWord();
            verb_wordnum++;
        }
        special_number=TryNumber(verb_wordnum);
        results-->0=##NotUnderstood;
        results-->1=2;
        results-->2=1; special_number1=special_word;
        results-->3=actor;
        consult_from = verb_wordnum; consult_words = num_words-consult_from+1;
        rtrue;
    }

!  **** (I) ****

!  If the player was the actor (eg, in "take dfghh") the error must be printed,
!  and fresh input called for.  In three cases the oops word must be jiggled.

    if (ParserError(etype)~=0) jump ReType;
    pronoun_word = pronoun__word; pronoun_obj = pronoun__obj;

    if (etype==STUCK_PE)   { L__M(##Miscellany, 27); oops_from=1; }
    if (etype==UPTO_PE)    { L__M(##Miscellany, 28);
                             for (m=0:m<32:m++) pattern-->m = pattern2-->m;
                             pcount=pcount2; PrintCommand(0); print ".^";
                           }
    if (etype==NUMBER_PE)  L__M(##Miscellany, 29);
    if (etype==CANTSEE_PE) { L__M(##Miscellany, 30); oops_from=saved_oops; }
    if (etype==TOOLIT_PE)  L__M(##Miscellany, 31);
    if (etype==NOTHELD_PE) { L__M(##Miscellany, 32); oops_from=saved_oops; }
    if (etype==MULTI_PE)   L__M(##Miscellany, 33);
    if (etype==MMULTI_PE)  L__M(##Miscellany, 34);
    if (etype==VAGUE_PE)   L__M(##Miscellany, 35);
    if (etype==EXCEPT_PE)  L__M(##Miscellany, 36);
    if (etype==ANIMA_PE)   L__M(##Miscellany, 37);
    if (etype==VERB_PE)    L__M(##Miscellany, 38);
    if (etype==SCENERY_PE) L__M(##Miscellany, 39);
    if (etype==ITGONE_PE)
    {   if (pronoun_obj == NULL) L__M(##Miscellany, 35);
                            else L__M(##Miscellany, 40);
    }
    if (etype==JUNKAFTER_PE) L__M(##Miscellany, 41);
    if (etype==TOOFEW_PE)  L__M(##Miscellany, 42, multi_had);
    if (etype==NOTHING_PE) { if (multi_wanted==100) L__M(##Miscellany, 43);
                             else L__M(##Miscellany, 44);  }

    if (etype==ASKSCOPE_PE)
    {   scope_stage=3;
        if (indirect(scope_error)==-1)
        {   best_etype=nextbest_etype; jump GiveError;  }
    }

!  **** (J) ****

!  And go (almost) right back to square one...

    jump ReType;

!  ...being careful not to go all the way back, to avoid infinite repetition
!  of a deferred command causing an error.


!  **** (K) ****

!  At this point, the return value is all prepared, and we are only looking
!  to see if there is a "then" followed by subsequent instruction(s).
    
   .LookForMore;

   if (wn>num_words) rtrue;

   i=NextWord();
   if (i==THEN1__WD or THEN2__WD or THEN3__WD or comma_word)
   {   if (wn>num_words)
       {   held_back_mode = false; return; }
       i = WordAddress(verb_wordnum);
       j = WordAddress(wn);
       for (:i<j:i++) i->0 = ' ';
       i = NextWord();
       if (i==AGAIN1__WD or AGAIN2__WD or AGAIN3__WD)
       {   !   Delete the words "then again" from the again buffer,
           !   in which we have just realised that it must occur:
           !   prevents an infinite loop on "i. again"

           i = WordAddress(wn-2)-buffer;
           if (wn > num_words) j = 119; else j = WordAddress(wn)-buffer;
           for (:i<j:i++) buffer3->i = ' ';
       }
       Tokenise__(buffer,parse); held_back_mode = true; return;
   }
   best_etype=UPTO_PE; jump GiveError;
];