/* cs342 homework 7
   Dan J. Fraser (1219229) 
   
5] evaluate(ParseTree, Value) calculates the Value that corresponds
   to ParseTree in a manner similar to Section 11.1 of the Prolog
   text [An Introduction to Logic Programming through Prolog by 
   Michael Spivey].

6]  tokenize(Sentence, Tokens) says whether or not Tokens is the list
    of words that form Sentence.  It can't find the Sentence for
    given Tokens, but it can find the Tokens for a given Sentence.
    Since this program is processing English, tokens are the same as
    words.  A word can be a delimiter or a sequence of characters that 
    contains neither a space nor a delimiter, but is followed by a space, 
    a delimiter, or the end of the list.

    Grammar:
    
    question ::= "How much is" number_expression "?"

    number_expression ::= number
    number_expression ::= "the sum of" sum_number_list 
    number_expression ::= "the product of" product_number_list 

    sum_number_list ::= number_expression "and" number_expression
    sum_number_list ::= number_expression "," sum_number_list
    sum_number_list ::= number_expression "," "and" number_expression

    product_number_list ::= number_expression "and" number_expression
    product_number_list ::= number_expression "," product_number_list
    product_number_list ::= number_expression "," "and" number_expression
*/

parse("How":"much":"is":Tokens,question(ParseTree)) :-
   print("parsing."),nl,
   append(B,"?":nil,Tokens),
   not B = nil, 
   print("b: "),print(B),nl,
   number_expression(B,ParseTree).
   
number_expression(B,number(Y)) :- evaluate_number(B,Y).
number_expression(B:nil,number(Y)) :- evaluate_number(B,Y).

number_expression("the":"sum":"of":SumExpr,ParseTree) :-
   print("sum expr: "), print(SumExpr),nl,
   sum_number_list(SumExpr,ParseTree),
   print("sum expr done: "),print(ParseTree),nl.
   
   
number_expression("the":"product":"of":ProductExpr,ParseTree) :-
   print("product expr: "), print(ProductExpr),nl,
   product_number_list(ProductExpr,ParseTree),
   print("product expr done: "),print(ParseTree),nl.
   
sum_number_list(SumExpr,sum(T1,T2)) :-
   print("working on sum rule 1"),nl,
   append(T0,",":List,SumExpr), 
   not T0 = nil,
   print("T0: "),print(T0),nl,
   number_expression(T0,T1),
   print("T1: "),print(T1),nl,
   print("List: "),print(List),nl,
   sum_number_list(List,T2),
   print("T1: "),print(T1),nl,
   print("T2: "),print(T2),nl.

sum_number_list("and":SumExpr,T1) :-
  print("working on sum rule 2"),nl,
  number_expression(SumExpr,T1),
  print("SumExpr: "),print(SumExpr),nl,
  print("T1: "),print(T1),nl.

sum_number_list(SumExpr,sum(T1,T2)) :-
  print("working on sum rule 3"),nl,
  append(T0,"and":List,SumExpr), number_expression(T0,T1),
  not T0 = nil,
  print("T0: "),print(T0),nl,
  print("List: "),print(List),nl,
  number_expression(List,T2),
  print("T1: "),print(T1),nl,
  print("T2: "),print(T2),nl,
  print("List: "),print(List),nl.
  
  
  
  
product_number_list(ProductExpr,product(T1,T2)) :-
   print("working on Product rule 1"),nl,
   append(T0,",":List,productExpr), 
   not T0 = nil, 
   print("T0: "),print(T0),nl,
   number_expression(T0,T1),
   print("T1: "),print(T1),nl,
   print("List: "),print(List),nl,
   product_number_list(List,T2),
   print("T1: "),print(T1),nl,
   print("T2: "),print(T2),nl.

product_number_list("and":ProductExpr,T1) :-
  print("working on product rule 2"),nl,
  number_expression(ProductExpr,T1),
  print("productExpr: "),print(productExpr),nl,
  print("T1: "),print(T1),nl.

product_number_list(ProductExpr,product(T1,T2)) :-
  print("working on product rule 3"),nl,
  append(T0,"and":List,ProductExpr), number_expression(T0,T1),
  not T0 = nil,
  print("T0: "),print(T0),nl,
  print("List: "),print(List),nl,
  number_expression(List,T2),
  print("T1: "),print(T1),nl,
  print("T2: "),print(T2),nl,
  print("List: "),print(List),nl.