# Simple calculator grammar
class Calculator
  prechigh
    nonassoc UMINUS
    nonassoc FUNC
    left "^" "*" '/' '%'
    left "+" "-"
    right PERCENTAGE_OF
    right "="
  preclow
rule
  target: exp
        | assign
        | /* none */ { result = 0 }

  exp: exp '+' exp { result += val[2] }
     | exp '-' exp { result -= val[2] }
     | exp '*' exp { result *= val[2] }
     | exp '/' exp { result /= val[2] }
     | exp '%' exp { result %= val[2] }
     | exp '^' exp { result = result.power(val[2])}
     | '(' exp ')' { result = val[1] }
     | '|' exp '|' { result = val[1].abs }
     | '-' NUMBER  =UMINUS { result = -val[1] }
     | VARIABLE { result = Brain.lookup(val[0])}
     | NUMBER
     | FUNC exp { result = Maths::Functions.exec(val[0], val[1]) }
     | exp PERCENTAGE_OF exp { result = Percentage.build(val[0], val[2]) }

   assign: VARIABLE "=" exp { result = Brain.assign(val[0], val[2]) }
     | VARIABLE "=" assign { result = Brain.assign(val[0], val[2]) }

end

---- header
# Generated grammar file.
module Maths
---- inner

  def parse(str)
    @q = []
    until str.empty?
      case str
      
      # ignore whitespace
      when /\A\s+/
        
      # percentage handling
      when /\Aas a percentage of/
        @q.push [:PERCENTAGE_OF, $&]
      when /\Aas a % of/
        @q.push [:PERCENTAGE_OF, $&]
      when /\Aas % of/
        @q.push [:PERCENTAGE_OF, $&]
      when /\Aas % of/
        @q.push [:PERCENTAGE_OF, $&]

      # special terms
      when /\Api/
        @q.push [:NUMBER, BigDecimal.new("3.14159265358979323846264338327")]

      # variables and functions
      when /\A[A-Za-z]+[0-9]*/
        if Maths::Functions::FUNCTIONS.has_key?($&)
          @q.push [:FUNC, $&]
        else
          @q.push [:VARIABLE, $&]
        end
      when /\A\$/
        @q.push [:VARIABLE, $&]
        
      # numbers
      when /\A\d+(\.\d+)?([Ee]\d+)?/
        @q.push [:NUMBER, BigDecimal.new($&)]
      # when /\A\d+/
      #   @q.push [:NUMBER, BigDecimal.new($&)]
      when /\A.|\n/o
        s = $&
        @q.push [s, s]
      end
      str = $'
    end
    @q.push [false, '$end']
    do_parse
  end

  def next_token
    @q.shift
  end

---- footer
end