As a disclaimer, I'm new to object-oriented programming and to Ruby; so
I'm not sure if I'm even describing this problem correctly. Here goes:

I have an object called "formula" which has properties .string (the
original formula), .leftSub, .rightSub (left and right subformula of
the original formula) and .characterType (an array identifying each
character in .string as being a particular type - e.g., number, letter,
and so on).

Now, I have the following:

class Formula

def initialize
@string = nil
@leftSub = nil
@rightSub = nil
@characterType = Array.new
end

def string=(newString)
@string = newString
mapCharacter
findLeftRight
end

def mapCharacter
#This method goes through
#each character in .string
#and maps to @characterType
#array.
end

def findLeftRight
#This method finds and
#assigns @leftSub, @rightSub.
end

def wff

testFormula1 = Formula.new
testFormula2 = Formula.new
testFormula1.string = @leftSub
testFormula2.string = @rightSub

#Problem line:
puts testFormula1.characterType[0]

end
end

Here is the main program:

test = Formula.new
test.string = "A&B"
test.wff

Now, Ruby exits with the following complaint:

in `wff': undefined method `characterType' for #<Formula:0xbceb0>
(NameError)

It is as if I am not referring to the element of the array correctly;
but I can't figure out exactly how I should be referring to it. Any
help would be appreciated.