calculate.rb

#!/usr/bin/env ruby
$:.unshift(".")
require "treetop"
require "lisp"
require "pp"

pp LispParser.new.parse("1.1").calculate
pp LispParser.new.parse("( )").calculate
pp LispParser.new.parse("(+)").calculate
pp LispParser.new.parse("(-)").calculate
pp LispParser.new.parse("(*)").calculate
pp LispParser.new.parse("(/)").calculate
pp LispParser.new.parse("(+ 4 3 2 1)").calculate
pp LispParser.new.parse("(- 4 3 2 1)").calculate
pp LispParser.new.parse("(* 4 3 2 1)").calculate
pp LispParser.new.parse("(/ 4 3 2 1)").calculate
pp LispParser.new.parse("(/ (* 5 (+ 5 5)) 5)").calculate

lisp.treetop

grammar Lisp
    rule top
        evalable* {
            def calculate
                elements.first.calculate
            end
        }
    end
    rule evalable
        sexp / value
    end
    rule value
        float / integer
    end
    rule float
        [+-]? [0-9]* "." [0-9]* {
            def calculate
                text_value.to_f
            end
        }
    end
    rule integer
        [+-]? [0-9]+ {
            def calculate
                text_value.to_i
            end
        }
    end
    rule symbol
        ( "+" / "-" / "*" / "/" ) {
            def calculate
                text_value.to_sym
            end
        }
    end
    rule sexp
        "(" space function:symbol space list:(space evalable)* space ")" {
            def calculate
                list.elements.map(&:evalable).map(&:calculate).inject(function.calculate)
            end
        }
        /
        "(" space ")" {
            def calculate
                nil
            end
        }
    end
    rule space
        [ \t\r\n]*
    end
end