Help writing Reduce functions for arithmatic in matlab

I need help figuring out how to write a couple reduce functions. One is somewhat of an umbrella function and the second is a function to simplify an addition equation. Sorry, I know this looks like a lot. For the Umbrella function so far I have:

function Result=reduce(Expr)

fprintf('Reducing %s\n', toString(Expr))

type = Expr{1};

switch type

    case {'Add', 'Sub', 'Mul', 'Div'}
        Operand1 = reduce(Expr{2});
        Operand2 = reduce(Expr{3});
        Result = reduceArith(type, Operand1, Operand2);
    case {'Neg'}
    case {'Pow'}
    case {'Sqrt'}
end

and for the reduceAdd function i have:

function Result = reduceAdd(Operand1, Operand2)

Operand1 = reduce(Expr{2});

Operand2 = reduce(Expr{3});

if isNum(Operand1)&& isNum(Operand2)

    Result = {'Num', Operand1{2} + Operand2{2}};
else
    Result={'Add', Operand1,Operand2};
end
end

There is also an intermediate function:

function Result = reduceArith(type, Operand1, Operand2)

type = Expr{1};

switch type

    case{'Add'}
        Result=reduceAdd(Operand1, Operand2);
    case{'Sub'}
        Result=reduceSub(Operand1, Operand2);
    case{'Mul'}
        Result=reduceMul(Operand1, Operand2);
    case{'Div'}
        Result=reduceDiv(Operand1, Operand2);
end    
end

I thought that these all were correct but when I test out the reduce function i get this error:

Error in ==> reduce at 2

fprintf('Reducing %s\n', toString(Expr))

??? Output argument "Result" (and maybe others) not assigned during call to "F:\Milanel(UCONN)\CSE 1010\MATLAB\05 Symbolic Math\reduce.m>reduce".

Error in ==> reduce at 6

        Operand1 = reduce(Expr{2});

If anyone could help me figure out how to correct the error I would greatly appreciate it. I know this seems like a lot to look at.

[Andrew Newell]

What command did you use to call reduce?

[Andrew Newell]

What is the function toStr?

Answer 1

[Walter Roberson]

You need a default case that sets Result to the input if it is irreducible.