#
# Baccus - Naur Form (BNF) vocabulary
#

@prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .
@prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#>.
@prefix bnf: <http://www.w3.org/2000/10/swap/grammar/bnf#>.
@prefix : <http://www.w3.org/2000/10/swap/grammar/bnf-rules#>.
@prefix rul: <http://www.w3.org/2000/10/swap/grammar/bnf-rules#>.
@prefix n3: <http://www.w3.org/2000/10/swap/grammar/n3#>.
@prefix list: <http://www.w3.org/2000/10/swap/list#>.
@prefix doc: <http://www.w3.org/2000/10/swap/pim/doc#>.
@prefix log: <http://www.w3.org/2000/10/swap/log#>.
@prefix string: <http://www.w3.org/2000/10/swap/string#>.
@keywords a, is, of.


<> rdfs:comment

"""This set of rules process a BNF graph in its basic
cfg:mustBeOneOf BNF form and create the branching tables to drive a 
predictive parser.

See also cfg2bnf.n3 which expands the shothand ontology into the basic
BNF terms.
""".

#_____________________________________


# Enumerate options:

{ ?x bnf:mustBeOneSequence ?y} => { ?x optionTail ?y }.

{?x optionTail [rdf:first ?y; rdf:rest ?z]} => {
	?x 	bnf:branch [ bnf:sequence ?y];
		optionTail ?z.
  }.

{ ?x bnf:branch [bnf:sequence ?y] } =>  { ?y sequenceTail ?y }.

sequenceTail a log:Chaff.
optionTail a log:Chaff.

{ ?x sequenceTail [ rdf:rest ?z ] } => { ?x sequenceTail ?z }.

# What productions can follow each other?
# This is used for working out when to 

{ ?x sequenceTail [ rdf:first ?y; rdf:rest [ rdf:first ?z ]] } =>
	{ ?y bnf:canPrecede ?z }.

{	?x bnf:branch [
	    bnf:sequence [
		list:last ?y]].
	?x bnf:canPrecede ?z} =>
	{ ?y bnf:canPrecede ?z }.

{ 	?x bnf:canPrecede ?y.
	?y bnf:branch [ bnf:sequence () ].
	?y bnf:canPrecede ?z.
} => {

	?x bnf:canPrecede ?z.
}.


bnf:eof bnf:canStartWith "@EOFDUMMY". #  @@ kludge

# Have to separate the next three rules or cwm seems to
# get screwed up and assume there is no solution @@@
 
{ ?x bnf:branch [bnf:sequence [ rdf:first ?y ]].
  }  => { ?x bnf:TEST ?y }.

{ ?x bnf:TEST ?y .
  ?y log:rawType log:Literal. }  => { ?x bnf:canStartWithLiteral ?y }.

{ ?x bnf:canStartWithLiteral ?y .
#  (?y "(.).*")  string:scrape ?c     # Use whole string
 }  => { ?y bnf:canStartWith ?y }.

#______________________________________________________________



# Rules for determining branching

# A branch has  a sequence, which is the given BNF production, and
# one or more conditions, which are the strings on which to consider
# that branch.  N3 is a langauge in whch the look-ahead often is only
# one character, and may allways be a constsnt string rather than a 
# regexp (check).

# A branchTail is a sequnece which a branch could start with
{ 	?x bnf:branch ?b.
	?b bnf:sequence ?s.
} => {
	?b bnf:branchTail ?s.
}.

{	?b bnf:branchTail ?s.
	?s rdf:first [ bnf:branch [ bnf:sequence () ]];
           rdf:rest ?t
} => {
	?b bnf:branchTail ?t.
}. 


{ 	?x bnf:branch ?b.
	?b bnf:branchTail ?s.
	?s rdf:first [bnf:canStartWith ?y].
} => {
	?x bnf:canStartWith ?y.
	?b bnf:condition ?y.
}.



{ 	?x bnf:branch ?b;
	    bnf:canPrecede ?z.
	?z log:rawType log:Literal.
	?b bnf:sequence ().
} =>  { ?b bnf:condition ?z}.

{ 	?x bnf:branch ?b;
	    bnf:canPrecede [bnf:canStartWith ?z].
	?b bnf:sequence ().
} =>  { ?b bnf:condition ?z}.




#ends